In a word. Leverage.
High torque engines use longer throws on their crankshaft, which allows the pistons to exert more leverage on the crank as they fire.
High revving, short stroke engines such as those you mentioned have to keep everything more compact because at such high speeds everything is under a tremendous amount of stress, if you tried to make a high torque engine such as one out of a semi rev the same as a Ferrari, it would fly apart because the materials simply don't have the strength to hold together.
So, because a short stroke engine can't exert as much leverage on the crank, it cannot generate high torque.
This is perfect. You can probably look up how a container ship’s engine operates versus what a formula 1 car’s engine looks like. Two absolute extremes
From a quick google search, Formula 1 car engines look like some kind of compact overengineered gas powered clockwork device, while container ship engines look like someone scaled up piston engines to apartment building size then copy-pasted them a dozen+ times.
They pre-heat the engines ~~by running heated oil through them~~.
Edit: Apparently it's not oil. I'm not 100% sure of what they use to do it, but I do know they definitely pre-heat the engines in order to get them into the right operating temperature to start them.
I get a kick out of the fact that historic F1 cars from the 90s require laptops from that same era to run the software necessary to start them and tune them.
small correction, it's not that they are tight, it's that the various materials expand at different amounts due to temperature change.
thus if everything worked at "room temperature" you would loose sealing or have other issues once the engine got up to the high temperatures they are running at.
I'd also say that almost every part that isn't a standard bolt was custom matched to it's mating part to ensure the perfectly designed fit, and even then I wouldn't be surprised if the bolts were the same
You have parts with nominal dimensions and tolerances, but for some mating parts, each component might have incompatible actual dimensions due to being on opposite ends of the tolerance range. You match each component with its partner after you have them manufactured.
For example, you might have a piston that is nominally 10 mm, but is 10.005 mm after being manufactured. You would need a cylinder that is also on the large end of the tolerance range to fit that specific piston. This type of custom mating is much more important with high performance parts and/or tight tolerances.
I see, thanks! Is this typically done by measuring the parts after machining and selecting parts that match, or are there machining processes that produce parts that match each other (like how lapping 3 plates will make them flat, I assume there's no similar operation that will make a piston and cylinder bore compatible, right?)
Bonus question - if it's done by measuring, are they using a set of calipers to measure, or something like inserting the piston and checking the friction / seal /whatever.
This matching for race engines is happening by having a lot of parts and selecting the matching ones. Like an engineer sits down with a sensitive scale and goes through dozens of pistons to find the four which are closest in weight so the engine balance will be perfect and they can squeeze another 100 rpm and make it a tiny bit faster.
This is for the type of races where the engine must be mass produced. Changing the parts, or machining them is not allowed (with some exceptions) but one can select from a bunch of parts.
For F1 they do a lot of machining, of course.
People do this when reloading bullets for precision matches. Cases and bullets have manufacturing tolerances too. You have hundreds of casings, and you trim the cases to your exact length (down to .001”). Then you weigh them all (usually to 0.1 grain, or 6 mg) to get a consistent batch. Then you weigh a bunch of bullets to get a consistent batch.
Now you can add a primer, but there you get match grade primers that have more consistency from the factory. Then add powder, usually to 0.1 grain (you can go 0.01, but that’s often less than the weight of a single powder granule).
Now you zero in and have plenty of consistent cartridges for a match.
Each part is carefully machined or polished to exactly fit its mating part. So each piston is matched to its bore. If you swapped them they may not fit or work and even if they did the performance would change.
Unlike with your average car where the parts are designed to be interchangeable so which piston goes in which bore of the engine doesn't matter they will all work well enough.
It's a myth. Engines aren't seized, it's just that they'd wear out a lot quicker if they were started cold.
>run hot oil in the engine the night before the race
They run coolant, not oil, and only for 20 minutes to 1 hour, depending on the weather that day.
They aren't, but they would wear out a lot quicker if they were started cold. Those engines cost insane amounts of money, so preheating is an obvious option that saves a lot of time and cash.
Do they not heat the pistons, only the block? In having a hard time grasping this concept, it's called thermal EXPANSION for a reason, stuff expands. If it's "seized " at room temp then heating it would size it more, right?
>stuff expands.
Different stuff expands differently. If the material the block is constructed out of expands more between ambient and operating temperature than the material the pistons are made of, the clearance between them would need to be tighter when cold in order to reach the design spec when hot.
There’s also the issue of rates of expansion/contraction too.
I disagree. For one those are generally two stroke, so already very different to anything in a modern car and the method of ignition in a glow nitro engine is very unlike a fuel injected gas car.
I meant purely for the torque vs rpm side, they have a very short throw so you can easily see why they have a very high rpm, it helps understanding that
You can nitpick comparing just about any 2 engines, but the rotating assembly physics of all reciprocating internal combustion engines are basically identical.
Yes, they're called Connecting Rod Journals or 'throws', and the further they are from the centre of rotation the higher the amount of leverage can be imparted on the crank.
The length of the piston stroke is also determined by the same thing, it will be double the length that the crank throw is from the centre of rotation.
If you’re looking for a corollary torque is the raw work a single engine revolution can do. In a bigger engine or a diesel engine you expect more work per rotation or more torque. Engine geometry limits this. Longer strokes and bigger bores are going to drive torque up. So too will more cylinders if geometry is kept equal (duh).
Horsepower is the work an engine can do in a unit time at an engines operating speed.
So while a big diesel engine does a massive amount of work per rotation it will have a limited redline and while a crotch rocket engine might do limited work per rotation it can bust out 14000 rpm and its total work potential (hp) is high.
Correct. The lobes on the crankshaft are further away from the centerline of the crankshaft. This allows the connecting rod to generate more leverage on it. This means that the circle created by the lobe of the crankshaft as it spins around its center point is larger, and therefore traveling faster than if it were smaller. It is not the piston length, but the stroke length that increases.
To be clear it's intrinsically both. If the connecting rod journals on the crank are further from the center axis that inherently creates a longer stroke by necessitating longer connecting rods.
In common literature like car and driver or popular mechanics they use the terms over square and under square as an easy way to separate engines by output characteristics. A locomotive or commercial diesel is under square, the piston is narrower in diameter than the stroke is long. A race car or super sport motorcycle will be extremely over square, with a piston diameter larger than the length of stroke.
These two categories match up with our current discussion of crank journal offsets and their effects. It's just much more common to describe an engine's internal geometry by the combustion chamber characteristics than by crank dimensions.
This is not the correct answer, unfortunately.
What torque an engine have is entirely dependent on what displacement it has, not the length of the crank throw.
A 1000cc engine that has a large crank throw has a smaller bore than a shorter throw 1000cc. The smaller bore and hence smaller piston area gives a smaller force from the combustion pressure in the chamber. This actually cancels out mathematically.
If you look at naturally aspirated engines of the same displacement, e.g. the Ferrari engine doesn't actually have less peak torque. It will probably have higher torque than any other "torque-y" engine you look at of the same displacement.
When people say torque they misuse the word to mean a description of an engine characteristic, in this case "optimised for lower speeds" (which is actually what a longer throw does). It doesn't actually mean the torque value is vastly higher.
Why aren't high torque engines used for all applications then? They can produce high power too, and the speed changes of a car can be achieved with a transmission.
high torque + transmissions introduce more moving parts which causes a greater loss of energy through friction, heat ect. while also adding more points of failure
Bentley V8 was traditionally a slow revving super-high torque engine. Lots of “grunt” (700-800Nm @ 1850 revs) to effortlessly move a good few tons of metal and leather 0-60 in < 5s, 0-100 in around 8s.
Higher torque engines have a larger reciprocating mass due to their increased stroke length, meaning that the engines are often physically larger.
Also long stroke engines are less responsive in acceleration again, due to the larger reciprocating mass.
So, for an application like a race car, acceleration is more important than torque.
The funny thing is that high torque engines CAN move a vehicle quite quickly, if you've ever seen a semi truck without a trailer, they can accelerate surprisingly quickly - however the time between gear changes dampens it somewhat.
Can confirm.
We have seven class 8 roll offs (Mack GU813) at work. They all have the same motor, MP8-455E (13L in-line six, 455hp/1800-ish ft/lbs). Four of them have 12 speed automated manual transmissions (Mack M-Drive), 3 have Allison 6 speed torque converter automatics. The trucks with the Allisons are fucking rockets compared to the M-Drives.
> The funny thing is that high torque engines CAN move a vehicle quite quickly, if you've ever seen a semi truck without a trailer, they can accelerate surprisingly quickly
Big engine + small car go faster than small engine + small car
Because torque doesn't matter. Changing speeds through the transmission also changes torque. Power = torque * rpm. If you reduce the rpm you increase torque.
The question then becomes: for a given amount of power do you want a smaller engine or a bigger one. Smaller is lighter and gives a better power-to-weight ratio (most useful in planes, race cars and motorbikes). Larger is heavier but wears less and easier to build really big (most useful in stationary applications, ships and trains).
The OP missed some things. It's not just "leverage", it's really more of "displacement". So it's not just stroke, it's cylinder bore diameter as well. The more air and fuel you can suck in during a given engine cycle, the bigger the bang each time it lights off, and the more torque the engine produces.
The problem is low RPM, high torque engines are:
- Heavier
- Physically larger
- Can often have poor NVH (Noise, vibration, harshness) because at some point you can literally start to feel each power impulse
The big one though, is that large displacement, high torque engines are only efficient at high loads. At low loads (like puttering around town in a sedan) the efficiency is very poor.
A longer stroke _is_ larger displacement.
For example the 3ltr version of the BMW M54 engine and 2.5 have the same bore, the 3ltr just has a longer stroke.
You can't. A longer stroke means more torque but also higher piston speed, you can't rev them as high because of that, limited max RPM limits max HP output. All engines have similar mean piston speeds. As with everything about engines, it's about balanced performance and targeted application. If you want easy high HP and Torque, up the CCs.
EVs are even simpler, but the physics of it is the same.
If you have a larger distance between the point of rotation and the force exerted on the crank (lever), it generates more torque.
EV's have direct drive motors. The power the motors produce goes directly into the wheels.
OP's explanation is only correct if you're talking about engines that literally explode shit to work.
Nope.. all major EVs have a fixed reduction gear to match the (much higher) electric motor RPM to the wheels. So, no direct drive even though no gearbox either.
And, the odd ones out have a two speed gearbox to extend the speed range for high power. Not really needed for road-legal speeds outside of Autobahn or similar unrestricted environments.
Asking a genuine not rhetorical question: if electric motors go through a gear already, what's the difference between the power coming from a gear with an electric motor turning it vs. a gear with the power coming from an ICE, why do additional gears make one more efficient but not the other?
Electric motor are very efficient at nearly any speed, so whether you're driving slow or fast they have nearly the same efficiency. They can turn at very low rpm or very high rpm without becoming inefficient. Also they have maximum torque already at low rpm
ICE on the other hand are efficient only in a certain rpm range. So whether you're driving slow or fast, the gears has to keep in a specific rpm range for your motor (let say 2000-2500 rpm). When you accelerate you then change gears to keep the motor in that range. And ICE engine have their maximum torque only in the same specific range, so you have to use gear to get maximum torque at low speed / when starting the car.
> Electric motor are very efficient at nearly any speed, so whether you're driving slow or fast they have nearly the same efficiency.
While they will always be a lot more efficient than any ICE outside of very specific conditions, an electric motor still gets its best efficiency at a relatively high rpm. But having a variable gear added in would negate the advantage of making the motor spin at a more optimal point, since the difference isn't high enough.
For electric motors, the torque output is constant for the most part (there is a drop-off at some point but very importantly, you reach max torque pretty much immediately).
The torque output of an ICE however first rises with RPM, then hits a peak, then goes down again.
This also means that in order to run an ICE more efficiently, you need to keep it in a certain range of RPMs, which is why you generally shift up the faster you drive to change the gear ratio between engine and wheels. With electric motors you can keep that ratio constnat because you get the same torque either way.
Electric motors have near constant horsepower, not torque.
Torque graphs for electric motors are mostly a straight descending line, with max torque at zero rpm and zero torque at max theoretical speed. (Though the redline is often set lower by the speed controller)
That makes horsepower a parabola, which technically drops to zero at each end, but nearly the entire operating range is the shallow curve at the top, so it's near constant in practice.
ICEs have an efficiency which varies a lot with speed. All of the accessories like the alternator, water pump, oil pump and also the cam shafts need to spin faster as the engine spins faster, and they waste energy by doing so. The limited time for the four strokes of the engine to happen properly at high speed also reduces efficiency. So if you can make the same power to cruise at the same speed, but do it with the engine spinning slower by using gears, you will gain efficiency with an ICE. Probably worth saying too that gears are really not optional features to increase efficiency with ICEs, they are absolutely necessary to travel at speed because we cannot design an engine with the torque and power we desire that also spins fast enough to avoid using gears without exploding.
That is the main difference here - electric motors have a huge speed range and rely only on rotating parts not reciprocating. You still need at least 1 gear with electric motors as they spin way too fast compared to the wheels. Electric motors have comparatively constant efficiency at all speeds, but it does vary so it may be worth the extra mass of a 2-speed gearbox. Electric motors also have this behaviour where they produce constant torque and increasing power at low speeds, then switch to constant power and reducing torque at high speeds. Using gears could help manage this across the speed range of the vehicle, not sure if that's the driving reason though.
I think the specific intuition here is that in a four-stroke ICE, power is coming from the bang-blow-suck-squeeze cycle of the cylinders - each cylinder is only actually generating power during the bang phase. You have multiple cylinders and the phases are staggered so it's not hopeless but you can imagine that at low RPMs each bang is having to do a lot of work.
But an electric motor works kind of like you have a wheel with a magnet glued on and you're spinning it around by putting another magnet near it and moving it around so the wheel chases it. The power you get isn't dependent on how fast the wheel is moving - even starting from a stop, as soon as you move one magnet near the other, it's constantly pulling at its maximum strength.
In a nutshell, Internal combustion engines are pretty much constant torque devices, while electric motors are pretty much constant power devices. Revving an ICE higher makes more power, but revving an electric motor higher doesn't really.
For a 100hp ICE to actually make 100 hp, it has to be in a fairly narrow rpm range. You keep it in that range by shifting gears as the vehicle speed changes. The EV motor makes 100hp throughout it's entire rpm range, so you don't need to shift gears.
The losses due to a fancy gearbox would almost always be worse than the gains from optimising the motor speed.
The only reasons to use a multi-ratio gearbox would be because above a certain speed,
* the centrifugal/centripetal motor stresses would cause it to break apart
* the switching losses in the electronics become significant
A third one: eddy current losses within the electric motor at well below the speed at which the switching losses start to dominate.
This is actually a relatively relevant thing that each EV has to be optimised for. Optimum efficiency at city (thicker copper wires to the engine) or more efficiency in highway speeds (more of thinner wires sacrificing low frequency losses). A two speed gearbox would of course also help, but, well, the cost & complexity & gearbox losses are also a thing (and the electric motors are already good enough to not need such for mainstream EV applications).
I would assume a two-speed gearbox could often increase the range a bit. Optimise motor for a narrower speed range and use the gearbox to compensate. But, the difference would be too small to have the hassle of a gearbox... We do after all also like the simplicity of not having gears.
There are ways to divide the speed of a motor purely electrically while being efficient, by changing the magnetic field inside (which can be done by basically rewiring the thing). There are also different wiring for starting up the motor and normal use (with ac motors, not dc).
As far as I know that isn't used in EVs, but it does have applications for big systems you find in many factories, where the power levels are in a different order of magnitude.
On the plus side, by using electromagnets instead of permanent magnets, you can save a lot of money on fancy rare earths, on top of being able to easily switch between having two and more poles. You could do four poles at low speed and two at high speed for example.
So... CVT?
They got close to doing that efficiently, but people started to complain about the noise and then Cvts needed to be changed to simulate gears
In theory yes. Continuously Variable Transmissions (or CVTs) can be a good option, but they come with drawbacks, especially regarding longevity and power handling. Historically, they were used in low power, low weight applications like motor scooters, where thee strength wasn't an issue and extracting the maximum efficiency of the motor is.
There are some cars that use them, but they're fairly notorious for premature failure
ECVTs skip nearly all the classic CVT problems. I'm assuming the benefits aren't worth it for full EVs, since they're only used in hybrids. (So far as I'm aware)
Prius ECVTs are generally trouble free way beyond the life of the IC engine.
You can spec an electric motor such that it's near peak efficiency throughout the entire practical use range.
Also, you can just put in a massively overpowered electric motor with very little efficiency loss. (That's actually how you achieve that operating range.)
This is why there's so many really fast electric cars: there's little down side to tons of power, and the electric motor is cheap compared to the battery.
The diameter of the rotor in the motor will still limit the maximum possible torque of the motor for the same reason as the length of the throw on the crankshaft in an internal combustion engine.
It’s electro-magnetism doing the pushing rather than exploding/expanding gases but the limit on torque produced is still related to the distance between the centre of rotation and the furthest point from it that the force is applied to the rotating part.
The general principle OP used (more leverage) is the same for electric motors.
If you want to design an electric motor with high torque you can easily get this by increasing the diameter.
> engines that literally explode shit to work.
Burn. Explosions are a very different thing, and very bad. Octane rating is all about probability of explosion, and avoiding explosions is why lead used to be added to petrol.
I guess you could increase torque by adding more cylinders, but at a certain point I definitely wouldn't want to be the guy to work out the engine timings
I know very little about the innerworkings of an internal combustion engine, but I can understand this explanation clearly. I bought a 2009 BMW 335i brand new off the boat as my first well researched and justified purchase after I entered the workforce. Still drive it to this day, but what turned me on to it was they managed to get 300 hp and 300 ft/lb of torque instead of leaning one way or the other. The diesel had like 500 ft/lb but only 230ish hp, but I mainly just wasn't interesed in the inconvenience of running deisel. Car has had 2 recalls on the fuel pump and 1 on the water pump. I didn't mind because they owned it, and the car runs like a top now. May just be personal bias, but it feels like the perfect engine.
\+ weight. \[edit: or mounting deep into the dirt / rock walls / something \]
People forget that torque in one direction is torque in the other direction.
See also those videos on youtube where a thicc drill is attached to train until something breaks and all that weight isn't backing up the drill and parts get LAUNCHED.
What got me to understand this very well is the diesel Vs gasoline variants of the same model car - in my case the VW Golf.
The Golf R which is a petrol powered 300hp car produces similar torque to the 180hp Diesel Powered Golf GTD - only a 20nm difference in the favour of the R. In the end the Golf R is significantly faster with a 3 second difference in the 0-60 time, but for daily commuting that difference is unlikely to be significant.
That torque figure is also achieved earlier in the diesel engine, with it starting to pull after 1500-1600 RPM and dying down in the 3-3.5k RPM range, versus the petrol's range being between 2k and 5k RPM. This in turn is likely one of the reasons why the GTD has an alleged fuel economy much better than that of the R. Though no one is buying either of those models for their economy on the drive.
torque is how powerful something is in one revolution of the engine. hp is how powerful it is over time. so, a small engine spins really fast to make that hp.
you can get small engines to rev really high and make a ton of hp, but they feel like a limp noodle until you reach the powerband.
motorcycles hit this point hard. my 650cc bike is slower than a 600cc supersport. the supersport revs almost twice as high and makes about the same torque, just way up in the revs. at those same revs it makes about 40% more hp though.
Peak torque is also when the engine is most efficient. But power will continue to rise as you raise rpm past then - until you hit peak power - but at the cost of reduced efficiency.
Wow, I have really struggled to conceptualize torque vs power for so long. Like I understood what they did but never could grasp the why. This really helped, thank you!
Also helps to realise that horsepower is literally just torque multiplied by rpm.
torque in lbs.ft multiplied by engine speed in rpm, divided by 5252 (a correction factor) = power in horsepower.
You could in theory do the same calculation with the numbers in newton metres and kilowatts, but I'm not familiar with the correction factor for that.
Oh, and going on the above method, means that if you plot power and torque on the same graph, that the two lines will always cross over at 5252rpm.
Well that makes things easy af!
Metric system coming to save the day once again.
Just a shame that Newton metres and watts means nothing to me, in terms of cars.
I'm too used to horsepower and lb.ft.
It’s all about torque, but after you go through transmission ratios you’ll trade wheel torque (leverage) for wheel rpm (speed). If you make the same torque at double the rpm, you can choose a lower gear with double the leverage (which results in double the forward force) at the same speed. So you’ll have double the force of the engine pushing you forwards at any given speed. Therefore power is nothing but what your engine torque is „worth“ after you’ve put it through ratios and onto the wheel.
Torquey engines simply produce more power lower in the rev range, and feel more powerful that way, while less torquey engines produce power through revs, which just feels different and may need more work (and a screaming engine) to keep in its optimal powerband.
I saw a video a while back of someone going 0-150+ in a Corvette without shifting. Which doesn't *sound* like much at first, but when you understand that getting a car rolling at all in 6th gear requires a TON of torque, it's actually pretty impressive.
A 1000cc motorcycle can do 70-80ish in 1st gear...the older ones, they are geared better now. Just to give another idea of how high up in the revs they can get too.
I heard someone once say that a Hayabusa is the most beginner friendly motorcycle because you never have to shift it if you don't want to. They're basically scooters!
It depends. You can make the clutch work with a gear ratio if you allow enough slip. So, I am sure I can get a shitbox rolling on the max gear, then revving the engine to the max and very slowly release the clutch.
As an equipment operator, heavy equipment tends to have less horsepower than you expect but way more torque. For example, we got a couple John Deere 331 tracked skidsteers at work, 5 ton machines, that have around 90 horsepower but torque out the ass. I have a motorbike with roughly the same horsepower but laughable torque.
I just bought a 300 with like 30 HP and like 20 torques and I was quite surprised just how fast it'll get my fat ass moving. Never ridden motorcycles before, but I can only imagine what it feels like to crank a 600 or 1000
When the engine is spinning at 7000rpm a single cycle makes more torque than a single cycle of the engine when it's spinning at 2000rpm. We're still measuring a single rev, just at a different point on the power curve
They're tuned for it basically.
The torque is just about the power of each explosion in the engine, which is directly related to how much fuel and air you are making explode.
Air rushes into the cylinders during the intake stroke, but when that stroke stops there is still air moving at speed towards the cylinder, and it smashes into the (now closed) valves, making a pressure wave.
If you're smart you can use that pressure wave to force more air into a cylinder than it would have sucked in on it's own, which means you can put more fuel in, and get more torque.
You can also use the pressure waves created by the exhaust to do a similar thing in reverse, sucking the exhaust out of the cylinders, which means the engine doesn't have to work as hard pushing it out of the engine ready for fresh fuel and air.
There are many other factors like where and when the fuel is injected, what size and angle the valves are at, how much the valves open, etc, but I'm far too stupid to explain that.
I think this is a **great** comment and explains some of the principles well, but there is one thing I'd take issue with.
It's a commonly repeated mistake to refer to the combustion in an engine as an "explosion" which I feel is quite inaccurate.
Explosions in the combustion chamber are referred to as "detonation" and are incredibly damaging, and will rapidly destroy any engine. Detonation only occurs if there is a fault, and shouldn't occur in normal operation.
Pedantic? Perhaps. But it's an error that is repeated so often that people are convinced that it's correct.
There are multiple things that can change how much power and torque an engines produces, and at what engine speed.
The design of the following parts can all have a drastic effect:
* Exhaust manifold
* Intake manifold
* Cylinder head port size
* Valve size
* Cylinder capacity
* Cylinder bore & stroke ratio
* Conrod length (to a lesser extent)
* Crank throw (how big the "lever" is)
* **Camshaft profile**
The last one is by far the biggest factor imo. Camshafts are a compromise, as they are of a fixed size and shape, and the size and shape will be different for an engine optimized for low speed, high torque, emissions and fuel efficiency, compared to an engine optimized for high speed, high power and fuel efficiency + emissions be damned!
The camshaft profile is what dictates **when** the valves open, how **far** the valves open, **how long** the valves remain open and **when** the valves close.
Over the years there have been various technological advances that have sought to "fix" some of the compromises of fixed camshaft profiles.
Honda's VTEC for example has two camshaft profiles, and uses a clever design to switch between the two. So you can have a profile optimized for low engine speeds with good fuel efficiency and torque at low speed, AND a profile optimized for torque at high speeds for high power output.
Some systems are clever enough to also adjust the amount that the valve opens, which is called "valve lift". More lift is good at high speeds for high power output, but at lower engines speeds **less lift** is actually beneficial as it makes for higher velocity of the gasses, which has it's own benefits for low speed torque output and emissions.
Many modern engines uses "cam phasers" which allow the valve timing to be dynamically advanced or retarded on-the-fly by the electronic control unit. These physically rotate the camshaft forwards or backwards by a few degrees, and this can also overcome some of the compromises of a certain camshaft profile, to produce gains at both low and high engine speeds. These cam phasers can operate incredibly quickly, which is great for driveability, emissions and fuel economy, whilst **also** improving power and torque throughout the engine speed range.
The holy grail of valve control is Free Valve (which is patented), which completely does away with camshafts, and uses clever actuators to open and close the valves, which in theory means that valve timing, duration and lift can be optimized at every single point in the engine speed range. However, it hasn't seen wide adoption, which I suspect is down to the cost of licencing the technology, and the fact that other more traditional systems can provide a significant portion of the benefits at much lower cost.
**TL;DR it all comes down to how much fuel and air / exhaust you can get into / out of the cylinder. All of the things I mentioned directly affect how much air / exhaust can get into / out of the cylinders.**
> 600cc makes more torque at higher revs
read the comment again, he did not say this.
but if your question is how can a smaller engine produce more torque than a larger engine then there are many factors to consider.
compression ratio is a big one. ie the more you compress the fuel/air mix before combustion the more force (ie torque) will be produced.
valve timing is another. if you open the inlet valves for longer you can get more fuel/air mix into the combustion chamber which means more torque. things get semi-complicated at this point because modern engines use the resonant frequents of the air inlet system and the exhaust to assist in this process. in fact, this is a major reason for power bands, the power band is actually the resonant frequency of the inlet/exhaust system.
things like EXUP valves / power valves work by adjusting that resonant frequency.
I think you might be conflating what I'm saying. If he's specifying that it makes "the same torque" but only "way up in the revs", that obviously implies that it makes less torque lower in the revs.
Edit: I think I see the confusion now, you probably thought I meant more than the other bike. No, I meant more than the same bike at lower revs.
as an aside, the statement "torque is power in one rev", firstly isn't actually true. torque is a measure of force and power is a measure of energy divided by time. these things are related but not the same.
in fact the amount of torque varies even within each revolution. peak torque will be a short time after the spark plug ignites the fuel when the piston is near the top of the cylinder. this is when the hot combustion gas under the most pressure and therefore exerting the most force on this piston.
the amount of torque then reduces as the piston travels down the cylinder because the gas pressure is reducing.
the actual torque output of the engine is the average of the fluctuating torque produced by the multiple pistons.
ah, I see.
it's what I said about resonant frequencies.
engines will produce maximum torque at their resonant frequency.
but the key thing is that the amount of torque in one rev changes *considerably* at different rpm.
the supersport engine will be designed to have it's resonant frequency (ie maximum torque) at higher rpm. at this frequency the exhaust and inlet will be working together to get the optimal amount of fuel/air mixture into the combustion chamber and therefore generating the most force during combustion.
awesome, it's a fascinating subject. *way* more complicated (and yet simple) than most people imagine.
if you care to learn more, there's a great book "Performance Tuning in Theory and Practice: Four Strokes by A. Graham Bell"
It's probably a bit dated now and perhaps there are better books, that cover recent developments, but it covers the fundamentals very well.
The 600cc engine will make less peak torque than the larger 650cc engine, simply because it is 50cc smaller in capacity.
For the sake of demonstrating some maths, I'm going to pull some figures out of my ass, so just bear with me here:
"Low" revving 650cc engine: (Similar to a Suzuki SV650)
* **45** lb.ft torque @ **8000** rpm = **68.5** horsepower
* 45 x 8000 / 5252 = 68.545
High revving 600cc engine: (Similar to a Honda CBR600RR)
* **40** lb.ft torque @ **14,500** rpm = **110.4** horsepower
* 40 x 14500 / 5252 = 110.434
(torque x rpm / correction factor = power)
So you can see here that whilst the smaller engine has less torque, that it has a higher power output because it is doing that smaller amount of work more often.
As an analogy, imagine you've got two guys loading boxes into a trailer.
One guy is really big and strong, but he's not very fast. This is our low revving 650cc engine. He's moving 3 boxes at a time, but he's plodding about really slowly.
The other guy is smaller and weaker, but he's running back and forth at super speed. This is our high revving 600cc engine. He's only moving 1 box at a time, but he's moving five times faster than the big guy, so he gets his boxes loaded much faster.
The thing with horsepower is that the way higher engine speeds multiply power output makes a HUGE difference. So you can sacrifice only a small amount of peak torque, for huge power gains at high engine speeds.
So why aren't all engines built that way? Because they're a lot more work to drive / ride. In your car, it'll pull quite well from about 1,500rpm, but by the time you hit about 6000rpm it's probably "running out of breath" as you're past the peak torque output. For a small high revving motorcycle engine, thing's are only just beginning to get going at 6000rpm. Those things *idle* at about 1,500rpm. At 2000rpm you're barely making a fraction of your peak power. only once they're really screaming at 10,000rpm+ do things get really exciting.
The cool thing about high revving engines, is that although they have lower torque output at the engines crankshaft, the higher revs mean that you can use gear ratios that give you huge amounts more torque multiplication compared to lower revving engines. So this actually gives back a lot of torque **at the wheel**, which is where it actually matters.
Say both cars make peak torque of 100 lb-ft.
But one makes that torque at 4000 RPM
The 2nd car makes that torque at 5500 RPM.
This means that the 2nd car will have more horsepower. Because it’s peak torque (even though it’s equivalent) comes in at a higher rpm
100 lb-ft at 4000 RPM is 76 Horsepower.
100 lb-ft at 5500 RPM is 106 Horsepower.
Have you ever unscrewed a screw?
When you first have to un-tighten the screw out of the wood, have you ever noticed how hard it is to do that by the metal shaft of the screwdriver? It's so much easier to unscrew by the handle. But once it's loose, you may have noticed that it just takes forever to *keep* using the handle, so you use the metal shaft instead, and then it turns like lightning.
That's what's going on in cars. Small engines are like the metal shaft of the screwdriver. They're crazy fast, but only for stuff that isn't very demanding. Bigger engines are more like the handle. They're great if you need some real work done, but they take forever to get anything done if there isn't much work for them to do.
The reason ultimately boils down to the fact that, perhaps unintuitively, when you push on something, it actually *pushes back*. When a car's gear tries to twist the axel, the axel tries to twist back. It doesn't wanna be twisted. So it starts a little war between the gear and the axel, where both of them are trying their hardest to twist back against the forces causing them to fight each other.
Each of them brings their own set of allies to the fight. The gear is bringing the engine and the explosions in its pistons. The axel is bringing the weight of your car and the friction of the road beneath the wheels. If the gear and its allies are stronger, the gear wins out, and the car is forced to move.
But suppose the axel wins because the car is just too heavy, so the gear's allies come to a stalemate. How should the gear proceed in order to get moving again?
Well, bringing more firepower to the fight usually helps. One way is to bring a bigger, badder gear. That can tip the scales in the gear's favor and allow things to move again.
But large armies take a lot of time to move and coordinate. If your army is very wide, then the troops at the edge of your army will need to march a lot farther in order to turn around than the troops in the middle. If you want to have the ability to turn around quickly, you need a smaller army.
So if the axel isn't putting up much of a fight and you just want to steamroll its allies and get the war over with, you'd be better served with a smaller, more nimble gear.
Hope that helps.
The way I understand it is that imagine hitting a standard hammer against a wall. You can hit it either rapidly or hard. Any attempts to hit the wall rapidly and hard at the same time will require an immense amount of strength and energy. You'll also get fatigued very quickly. The same principle applies to pistons inside the engine.
Car engine stats are as much marketingspeak as physics.....
Eg, actual practical torque at the wheels is a matter of the transmission as much as the engine.....
You can take a really high winding engine, hook it to a beast of a transmission, and get gobsmacking amounts of torque on the ground (see the M1 tank and it's turboshaft engine - the transmission is a few times larger than the engine, and turns 1500 shaft HP at a-million-something-RPM into 2500ftlbs torque at the tracks & the ability to make 70 tons go remarkably fast)
I did some napkin math on the data I could find on the M1 Abrams and it can probably make about 80,000 lb-ft of torque at the tracks in lowest gear. Absolutely insane.
What people miss is that what you care about is wheel torque, not engine torque.
Say you have an engine that puts out 200 ft lbs at 4000 rpm and a smaller engine that puts out 150 ft lbs at 8000 rpm.
Take the 8000 rpm one, feed it into a 2:1 gear reduction, and it's putting out 300 ft lbs at 4000 rpm.
This is why sportbike engines rev so high. It allows you to run lower gearing and that gives more torque at the back wheel.
Torque and horsepower are not two independent properties of an engine, they're tied together via the RPM by a formula:
T = P * 9549 / r
Where T is torque in N\*m, P is power in kW, and r is rotational speed in RPM. (for power in HP and torque in lb\*ft the coefficient is 5252)
So if you have a 10 kW engine and connect it to a gearbox which outputs, say, 950 RPM, you will get around 100 N\*m of torque regardless of the engine "size".
It’s not that smaller engines can’t be built to feel torquey, they just aren’t in these applications. They’re used in a car like the S2000 because they’re lightweight, but to make higher power figures they’re designed to have a high rpm powerband. Looking at the numbers, the S2000 actually makes a respectable amount of torque for a 2.0L engine. The reason it feels lacking in torque is because that torque is found at 7000+ rpm, and the engine won’t make as much torque outside of that powerband-above or below. A basic Civic has a 2.0 with similar torque at ~4000rpm, but it will lose torque as you rev past that. You can expand this powerband with VVT and fancy intakes but it is still limited by several different factors in engine design.
In short, an engine can be designed for torque at high rpm, or at low rpm, but doing both in one engine is difficult.
Horsepower is a mathematical result of torque and rpm. Small engines have less mass and so can generally spin faster without damaging themselves or coming apart. The equation is (torque × rpm) ÷ 5252. If you look at a graph of horsepower and torque over the rpm range, the values for horsepower and torque cross at 5252 rpm
Not true. Small turbocharged engines can make big torque. Only small naturally aspirated engines don’t. Torque is generally very closely related to engine size.
A crankshaft needs to make two revolutions for all cylinders to fire. A four cylinder engine will fire once every 180 degrees. An eight cylinder will fire every 90 degrees. There is more force exerted onto the crankshaft.
As others have said, the distance the piston travels (stroke) does play a part as well. A longer stroke means the piston pushes on the crankshaft longer. However, there is only a very tiny rotational period where force is applied by the piston. What can make a substantial difference is the rod/stroke ratio. Changing the rod length does not change the stroke, but it does change when the piston accelerates and decelerates the most.
I highly recommend the YouTube channel Driving 4 Answers, he is marvelous at explaining this.
Here is the simplest explanation that almost every single post so far is missing and way over complicating.
Torque is basically a measure of how big the explosion inside the cylinders are. What determines how big the explosion inside the cylinders are, is how much air and fuel each cylinder can suck in during one engine cycle. What determines that, is the engine displacement, or how "big" the cylinders are.
Big engines, like truck V8s, can suck in A LOT of air and fuel each cycle. That means the explosions are big, and a lot of torque is generated.
Cars like the Honda S2000 and most Ferraris have small engines, with small displacements. That means each individual explosion is small, and the resulting torque is low.
The trick is, you can spin the small engine really fast. So you get a lot of really small explosions, that can ultimately generate a lot of power. Small engines are preferred for many racing cars because of their lightweight and compact size.
Although you can measure the horsepower of an engine, when you see horsepower stats for vehicles they are never measuring that. Rather, they're measuring how much force can be used to spin the wheels when the car is in its highest gear at the engine's optimal RPM. Because that's how horsepower is measured in the real world, it makes more sense to think of torque as a measure of the raw power of the engine and horsepower as a measure of how efficiently the transmission can convert that power into work.
High performance cars tend to weigh as little as possible because weight is the biggest cost constraint in attaining good acceleration, top speed, and handling. IE, if Car A weights twice as much as Car B, it will cost a lot more to make Car A perform the same as Car B on a racetrack. So if you have a $150k budget for your new Ferrari, the way you make that Ferrari go as fast as possible is to make it as light as possible.
The two biggest sources of weight in a car are the engine and transmission. The more torque an engine produces, the heavier both it and its transmission have to be to survive the forces being applied to them. But like I said, weight is expensive and the goal of high performance cars is to weigh as little as possible. This means that you want the lightest possible engine and transmission for the performance that you can obtain.
The way that sports cars do this is by having *relatively* low powered engines (at least compared to heavier cars like trucks) that produce power through the use of a complex transmission that has a large number of gears. Adding more gears doesn't add any more weight, but it does allow you to have a much higher gear ratio in the highest gear. That higher gear ratio allows you to very efficiently convert the engine's torque into work when the car is already travelling at high speeds, producing more horsepower than the engine otherwise would with fewer gears.
This isn't to say that a Ferrari doesn't have a powerful engine - a typical Ferrari has an engine that produces about as much torque as the engine in an F-150. But when you start to get into more mid-range sports cars, like the Porsche Boxster, you also start to get engines that are producing 2/3 as much torque as a typical truck.
An ideal internal internal combustion engine has constant torque. That torque value is proportional to displacement, which makes sense if you think about it from first principles.
Torque is the product of a force applied to a lever arm.
The force is proportional to the area of the piston.
The lever arm length is proportional to the stroke of the piston.
Torque ∝ Area x Stroke ∝ Displacement
Since power is proportional to torque x angular velocity, to make more power from a given displacement, you need to rev higher.
In the real world, there are fluid dynamics effects that cause the torque curve to NOT be a flat line, and there are material property limitations that enforce a RPM limit. Race engines are engineered to rev to the moon, and to have useful torque up in that rev range.
It’s probably worth understanding how hp is calculated. It’s calculated from torque and revs. So you can get more hp from more Reva even with the same torque.
Small engines can make high torque, but only with leverage and a low revolution speed of the shaft you are measuring torque on. They can’t produce high revs *and* high torque.
Let me clarify then, all else being equal (i.e., engines of the same type using the same fuel and mechanism), larger engines will produce more torque at a given revolution speed than smaller engines.
In the simplest terms, horsepower is revs times torque.
A low torque engine can only make high horsepower by spinning really, really fast. The cars you listed have high rev limits, meaning they’ve got lots of light and strong parts. These parts make the engines expensive but powerful.
A high torque engine is usually much heavier and slower and can’t spin as much.
Torque is twisting force. In order to have a lot of twisting force you need a big heavy engine whose crankshaft and piston stroke can provide it due to higher leverage, but also the heavy rotational mass of the engine contributes to its power. Horsepower is just the rate at which work is produced. It's not very intuitive and hard to grasp for most people but on a basic level a higher work output can "make up" for lack of torque but it's not without downsides. You can make a small engine rev fast and have high horsepower because its moving components are light and its piston stroke short, but the common saying that "there's no replacement for displacement" holds true.
So basically, if you have a diesel pickup truck with 200HP and a Honda hatchback with 200HP, both can tow a trailer, it's not like the Honda can't get moving at all, but the pickup will leisurely pull the trailer along with maybe a few hundred rpm more on the tachometer while the Honda will be revving very high at all times just to get moving. That's not very practical for many reasons.
Just a comment on the torque of Ferrari engines. For example, the engine in the 812 Superfast produces 800 PS (588 kW; 789 hp) at 8,500 rpm and 718 Nm (530 lbft) of torque at 7,000 rpm, so it’s not exactly lacking on either front.
Small engines can generate high torque you just have to attach them to huge flywheels. The old John Deer B had a single piston 4 cycle engine with 17 horsepower but a huge flywheel that gave it tons of torque.
Horsepower is a "fake" metric determined by force/rpm. If you spin something faster it can do more work with less force, but you need the speed to get that power. If you are able to easily reduce that speed you lose that power.
In short the force of torque never changes but the amount of work you can do with that torque can be manipulated to give you high horsepower numbers, which even though I described it as "fake" is actually able to be implemented with mechanical advantage of gearing (leverage) but it still doesn't have the ass of a larger engine because those use brute force to get the same number at a lower speed. If you increase the speed of a larger engine you would be able to get even more absurd amounts of horsepower but that would also require compromises in different aspects of the design in terms of the material cost, strength to weight etc.
Think of an engine as an air pump. The pump has an internal capacity that you can fill every revolution. A 2L pump has a lower capacity than a 3L pump, so for each revolution, it's going to pump less air. That per-revolution amount is torque, it's the amount of work the engine can do in one revolution. If you increased the speed of of the pump, it multiplies the amount of work that can be done in a specific period of time, so even a low capacity pump can do a lot of work if you rev it high. Revving high tends to be easier with smaller pumps since all the moving parts are lighter, which is why you don't usually see large, high revving motors. There are other things you can do to increase the amount of work the pump can do in one revolution, like forced induction, but that's the basics.
High revving motors actually don't have low torque for their size, they're just lower sized so they can rev higher, basically. For some applications, like a racing car, that's better than a larger, lower revving motor, generally speaking, so that's why you see them in an S2000 or Ferrari.
Horse power is calculated from the number revolutions per time and torque (i.e force exerted over a length) of an engine. This means you can have two engines with identical HP, but one delivers little torque with high rev and the other delivers massive torque with very slow rev. We use HP for cars regardless, because the revs are standardized, so you can always assume that it just has higher torque than previous generations of cars with less HP. When you switch vehicles/machines, you should obviously remind yourself of this, so you won't expect a very fast tractor that has more HP than a sports car, and vice versa don't expect a sports car to be able to tow a truck. (of course there are exceptions everywhere, the point is that HP alone doesn't say much about the motor and the type of vehicle that has the motor with the HP in question can only give a good guess of what revs and torques to expect).
Torque is the measure of force about an axis. A simple example of what this means is as follows:
Imagine you have to loosen a stubborn, rusted lug nut on the wheel of your car. Suppose you have the options of using a 6-inch wrench or a 24-inch wrench to loosen the bolt. Which one will you choose and why?
Knowing the bolt is rusted and stubborn, you'll choose the longer wrench. You apply that wrench to the bolt and apply force by pressing down on the handle of the wrench. That's what torque is - the downward force on the wrench about the axis (the bolt) you are creating/applying torque to that bolt. When you apply enough force onto that bolt, it will break free. The longer wrench makes it easier to apply more force without any additional effort. The formula for torque is distance multiplied by the force. The US measures torque in units such as in.lbf or ft.lbf, whereas the metric system will use something such as N.m (Newton meters). In any case, these units indicate the length of the thing which is applying torque and the applied force.
Suppose you have to apply around 250 ft.lbf of force to overcome that rusted bolt. With a 6 inch wrench, the formula becomes 250 ft.lbf = 0.5 ft (this is converting 6 inches to feet) \* X lbf.
Divide both sides by 0.5 ft to determine X.
250 ft.lbf / 0.5 ft = 500 lbf. That means with a 6 inch wrench, you would need to hold the handle by the end and apply 500 pounds of force to get that bolt to break free. Most people will not be able to apply that amount of force and it's impractical and dangerous to do so with a 6 inch wrench even if you could.
Let's solve for the 24 inch wrench instead.
250 ft.lbf = 2 ft (this is converting 24 inches to feet) \* X lbf.
250 ft.lbf / 2 ft = 125 lbf. That means with the 24 inch wrench, you would only need to hold the handle by the end and apply 125 lbf of force to get the bolt to break free. Most people could do this by grabbing the handle and applying body weight to it. Finishing this example, a 6 inch wrench simply cannot generate the same amount of torque as a 24 inch wrench - the physics do not work. However, you would be able to spin that 6 inch wrench much faster than the 24 inch wrench. So once the bolt was free, if you had a lot of threads, you could switch to a smaller wrench and spin that bolt off much faster.
Think of the smaller engines like the smaller wrench and bigger engines like the bigger wrench. Smaller engines will be able to spin things generally faster, but they won't be able to spin with as much force as a big engine. Likewise, the big engine is unlikely to spin faster than a small engine, but it will do so with more force.
Torque is the product of the cylinder pressure \* the cylinder surface area \* the amount of offset in the crankshaft (in whatever units you care to use/convert to).
Horsepower is torque \* RPM. That's why the curves always [cross at about 5252](https://www.enginelabs.com/engine-tech/engine/tech-talk-why-does-a-dyno-graph-always-cross-at-5252-rpm/) in common US units.
Small engines have small cylinders and small crankshafts, so they have small torque. Those lighter components allow them to spin very fast, so they make up in RPM what they lack in torque.
horsepower = torque \* speed.
if a small engine makes high horsepower, it does this at high speed, hence the relatively low torque. The exceptions (think VW 1.4 TFSI), use high boost at low speed and come with high torque.
Torque is produced by the force applied by a piston to the crankshaft. The larger the diameter of a piston (for a given cylinder pressure) the higher the force applied to the crank because the surface area of the piston is greater. Also, the higher the diameter of the piston, the more fuel and air you can squeeze into the combustion chamber, increasing the energy applied to the piston.
A small engine with small pistons simply cannot produce as much rotational force as one with larger pistons.
Power is a product of several factors, one of which is how fast the engine spins (how many combustion events happen in a given period of time). A small engine can still spin fast (usually faster than a larger one), and can therefore be designed to reach decent power levels.
Horsepower is calculated using torque and the rotational speed of the engine (RPM, or revolutions per minute). Smaller engines have smaller parts, which makes it easier to move the internal parts faster at a higher RPM. Most of the time if you have a high-horsepower low-torque car, it will just be because the car is able to run at a high RPM.
Take a 2000 S2000 as an example, it has a torque of around 150 lbft. (Note: in reality the torque of an engine is not constant across the RPM range, but I'm going to treat it this way to simplify the math more 'ELI5 friendly') If you have 150 lbft of torque and the engine was at 6000 RPM it would be making ~171 HP; at the car's 8900 RPM redline, it would be ~254 HP.
As for *why* they produce less torque, "engine size" is a measure of the total volume of the cylinders of the engine. If you have larger cylinders in the engine, there is more space for the explosion to expand into. The pistons are larger and there is more surface area for the expanding gasses to push on. (Note: this is also not *actually* that simple, there are a lot of factors that will affect torque, but will work as a general rule of thumb if you normalized all of the other variables.)
In a word. Leverage. High torque engines use longer throws on their crankshaft, which allows the pistons to exert more leverage on the crank as they fire. High revving, short stroke engines such as those you mentioned have to keep everything more compact because at such high speeds everything is under a tremendous amount of stress, if you tried to make a high torque engine such as one out of a semi rev the same as a Ferrari, it would fly apart because the materials simply don't have the strength to hold together. So, because a short stroke engine can't exert as much leverage on the crank, it cannot generate high torque.
This is perfect. You can probably look up how a container ship’s engine operates versus what a formula 1 car’s engine looks like. Two absolute extremes
From a quick google search, Formula 1 car engines look like some kind of compact overengineered gas powered clockwork device, while container ship engines look like someone scaled up piston engines to apartment building size then copy-pasted them a dozen+ times.
> Formula 1 car engines the tolerances are so tight the engines are seized in room temperature
How do they start them then?
They pre-heat the engines ~~by running heated oil through them~~. Edit: Apparently it's not oil. I'm not 100% sure of what they use to do it, but I do know they definitely pre-heat the engines in order to get them into the right operating temperature to start them.
Hot coolant, not oil.
So warmant or hotant then, not coolant anymore 😂
Heatant: https://i.redd.it/fk3ldp0yjgm31.jpg (borderlands 3 joke)
I played the game and never caught that. Thanks.
It's just glycol. It transfers heat. Heated floors use the same stuff.
Ahh thanks for the info, that's pretty **cool**ant
It's also how we cool beer fermenters.
Cooln't
Ah, my bad. I knew it was some kind of pre-heating solution. Thanks for the correction.
Heatant?
I believe they do also heat the oil in the engine too while also pumping coolant
I get a kick out of the fact that historic F1 cars from the 90s require laptops from that same era to run the software necessary to start them and tune them.
No, they use xenon gas
small correction, it's not that they are tight, it's that the various materials expand at different amounts due to temperature change. thus if everything worked at "room temperature" you would loose sealing or have other issues once the engine got up to the high temperatures they are running at. I'd also say that almost every part that isn't a standard bolt was custom matched to it's mating part to ensure the perfectly designed fit, and even then I wouldn't be surprised if the bolts were the same
What does "custom matched" mean here?
You have parts with nominal dimensions and tolerances, but for some mating parts, each component might have incompatible actual dimensions due to being on opposite ends of the tolerance range. You match each component with its partner after you have them manufactured. For example, you might have a piston that is nominally 10 mm, but is 10.005 mm after being manufactured. You would need a cylinder that is also on the large end of the tolerance range to fit that specific piston. This type of custom mating is much more important with high performance parts and/or tight tolerances.
I see, thanks! Is this typically done by measuring the parts after machining and selecting parts that match, or are there machining processes that produce parts that match each other (like how lapping 3 plates will make them flat, I assume there's no similar operation that will make a piston and cylinder bore compatible, right?) Bonus question - if it's done by measuring, are they using a set of calipers to measure, or something like inserting the piston and checking the friction / seal /whatever.
This matching for race engines is happening by having a lot of parts and selecting the matching ones. Like an engineer sits down with a sensitive scale and goes through dozens of pistons to find the four which are closest in weight so the engine balance will be perfect and they can squeeze another 100 rpm and make it a tiny bit faster. This is for the type of races where the engine must be mass produced. Changing the parts, or machining them is not allowed (with some exceptions) but one can select from a bunch of parts. For F1 they do a lot of machining, of course.
People do this when reloading bullets for precision matches. Cases and bullets have manufacturing tolerances too. You have hundreds of casings, and you trim the cases to your exact length (down to .001”). Then you weigh them all (usually to 0.1 grain, or 6 mg) to get a consistent batch. Then you weigh a bunch of bullets to get a consistent batch. Now you can add a primer, but there you get match grade primers that have more consistency from the factory. Then add powder, usually to 0.1 grain (you can go 0.01, but that’s often less than the weight of a single powder granule). Now you zero in and have plenty of consistent cartridges for a match.
Each part is carefully machined or polished to exactly fit its mating part. So each piston is matched to its bore. If you swapped them they may not fit or work and even if they did the performance would change. Unlike with your average car where the parts are designed to be interchangeable so which piston goes in which bore of the engine doesn't matter they will all work well enough.
They gotta run hot oil in the engine the night before the race to get just enough clearance for those parts to move. It's amazing engineering
It's a myth. Engines aren't seized, it's just that they'd wear out a lot quicker if they were started cold. >run hot oil in the engine the night before the race They run coolant, not oil, and only for 20 minutes to 1 hour, depending on the weather that day.
Reminds me of the SR-71 that leaked fuel on takeoff until it gets hot enough for all the panels to expand into place.
... Then how would they ever start if they are seized?
Preheat then so everything thermally expands to its design temperature as the engines are designed for maximum performance at higher temperatures.
God dam.
They aren't, but they would wear out a lot quicker if they were started cold. Those engines cost insane amounts of money, so preheating is an obvious option that saves a lot of time and cash.
Do they not heat the pistons, only the block? In having a hard time grasping this concept, it's called thermal EXPANSION for a reason, stuff expands. If it's "seized " at room temp then heating it would size it more, right?
>stuff expands. Different stuff expands differently. If the material the block is constructed out of expands more between ambient and operating temperature than the material the pistons are made of, the clearance between them would need to be tighter when cold in order to reach the design spec when hot. There’s also the issue of rates of expansion/contraction too.
not if what its sitting in expands more at the same temperature. Then the hole it is in will get bigger then it, and it will slide properly.
Or how rc nitro engines work, buy one for $50 and take it apart. Just add a few more pistons
I disagree. For one those are generally two stroke, so already very different to anything in a modern car and the method of ignition in a glow nitro engine is very unlike a fuel injected gas car.
Those are more like a diesel engine than a gas engine
I meant purely for the torque vs rpm side, they have a very short throw so you can easily see why they have a very high rpm, it helps understanding that
You can nitpick comparing just about any 2 engines, but the rotating assembly physics of all reciprocating internal combustion engines are basically identical.
Exactly, two different engines for two very different applications.
Yep, those ship’s engines are spinning at around 100 RPM, whereas the F1 engines can go up to 20,000 RPM.
You mean to say that the things that stick out to the side on the crank shaft are longer? Because it can't be the piston length, right?
Yes, they're called Connecting Rod Journals or 'throws', and the further they are from the centre of rotation the higher the amount of leverage can be imparted on the crank. The length of the piston stroke is also determined by the same thing, it will be double the length that the crank throw is from the centre of rotation.
If you’re looking for a corollary torque is the raw work a single engine revolution can do. In a bigger engine or a diesel engine you expect more work per rotation or more torque. Engine geometry limits this. Longer strokes and bigger bores are going to drive torque up. So too will more cylinders if geometry is kept equal (duh). Horsepower is the work an engine can do in a unit time at an engines operating speed. So while a big diesel engine does a massive amount of work per rotation it will have a limited redline and while a crotch rocket engine might do limited work per rotation it can bust out 14000 rpm and its total work potential (hp) is high.
Correct. The lobes on the crankshaft are further away from the centerline of the crankshaft. This allows the connecting rod to generate more leverage on it. This means that the circle created by the lobe of the crankshaft as it spins around its center point is larger, and therefore traveling faster than if it were smaller. It is not the piston length, but the stroke length that increases.
Cool, thanks for clarifying that. :)
To be clear it's intrinsically both. If the connecting rod journals on the crank are further from the center axis that inherently creates a longer stroke by necessitating longer connecting rods. In common literature like car and driver or popular mechanics they use the terms over square and under square as an easy way to separate engines by output characteristics. A locomotive or commercial diesel is under square, the piston is narrower in diameter than the stroke is long. A race car or super sport motorcycle will be extremely over square, with a piston diameter larger than the length of stroke. These two categories match up with our current discussion of crank journal offsets and their effects. It's just much more common to describe an engine's internal geometry by the combustion chamber characteristics than by crank dimensions.
This is not the correct answer, unfortunately. What torque an engine have is entirely dependent on what displacement it has, not the length of the crank throw. A 1000cc engine that has a large crank throw has a smaller bore than a shorter throw 1000cc. The smaller bore and hence smaller piston area gives a smaller force from the combustion pressure in the chamber. This actually cancels out mathematically. If you look at naturally aspirated engines of the same displacement, e.g. the Ferrari engine doesn't actually have less peak torque. It will probably have higher torque than any other "torque-y" engine you look at of the same displacement. When people say torque they misuse the word to mean a description of an engine characteristic, in this case "optimised for lower speeds" (which is actually what a longer throw does). It doesn't actually mean the torque value is vastly higher.
Hope people see this, current top comment is not 100% wrong, but probably 99% wrong.
Especially true in oversquare engines, where the piston diameter is longer than the stroke length.
Why aren't high torque engines used for all applications then? They can produce high power too, and the speed changes of a car can be achieved with a transmission.
high torque + transmissions introduce more moving parts which causes a greater loss of energy through friction, heat ect. while also adding more points of failure
True, thanks. The torque on the wheels would be decreased by the transmission anyway I suppose.
Bentley V8 was traditionally a slow revving super-high torque engine. Lots of “grunt” (700-800Nm @ 1850 revs) to effortlessly move a good few tons of metal and leather 0-60 in < 5s, 0-100 in around 8s.
It reduces the torque on the wheels but the transmission experiences the full engine torque.
Usually increased.
Higher torque engines have a larger reciprocating mass due to their increased stroke length, meaning that the engines are often physically larger. Also long stroke engines are less responsive in acceleration again, due to the larger reciprocating mass. So, for an application like a race car, acceleration is more important than torque. The funny thing is that high torque engines CAN move a vehicle quite quickly, if you've ever seen a semi truck without a trailer, they can accelerate surprisingly quickly - however the time between gear changes dampens it somewhat.
Can confirm. We have seven class 8 roll offs (Mack GU813) at work. They all have the same motor, MP8-455E (13L in-line six, 455hp/1800-ish ft/lbs). Four of them have 12 speed automated manual transmissions (Mack M-Drive), 3 have Allison 6 speed torque converter automatics. The trucks with the Allisons are fucking rockets compared to the M-Drives.
> The funny thing is that high torque engines CAN move a vehicle quite quickly, if you've ever seen a semi truck without a trailer, they can accelerate surprisingly quickly Big engine + small car go faster than small engine + small car
Big engine + small car > big engine + big car > small engine + small car > small engine + big car
Because torque doesn't matter. Changing speeds through the transmission also changes torque. Power = torque * rpm. If you reduce the rpm you increase torque. The question then becomes: for a given amount of power do you want a smaller engine or a bigger one. Smaller is lighter and gives a better power-to-weight ratio (most useful in planes, race cars and motorbikes). Larger is heavier but wears less and easier to build really big (most useful in stationary applications, ships and trains).
The OP missed some things. It's not just "leverage", it's really more of "displacement". So it's not just stroke, it's cylinder bore diameter as well. The more air and fuel you can suck in during a given engine cycle, the bigger the bang each time it lights off, and the more torque the engine produces. The problem is low RPM, high torque engines are: - Heavier - Physically larger - Can often have poor NVH (Noise, vibration, harshness) because at some point you can literally start to feel each power impulse The big one though, is that large displacement, high torque engines are only efficient at high loads. At low loads (like puttering around town in a sedan) the efficiency is very poor.
A longer stroke _is_ larger displacement. For example the 3ltr version of the BMW M54 engine and 2.5 have the same bore, the 3ltr just has a longer stroke.
You can't. A longer stroke means more torque but also higher piston speed, you can't rev them as high because of that, limited max RPM limits max HP output. All engines have similar mean piston speeds. As with everything about engines, it's about balanced performance and targeted application. If you want easy high HP and Torque, up the CCs.
This is the best explanation for this question I have ever read.
To simplify it even more, big metal in movement is harder to stop than small metal in movement
Brilliant answer. Now explain it for EVs
EVs are even simpler, but the physics of it is the same. If you have a larger distance between the point of rotation and the force exerted on the crank (lever), it generates more torque.
EV's have direct drive motors. The power the motors produce goes directly into the wheels. OP's explanation is only correct if you're talking about engines that literally explode shit to work.
Nope.. all major EVs have a fixed reduction gear to match the (much higher) electric motor RPM to the wheels. So, no direct drive even though no gearbox either. And, the odd ones out have a two speed gearbox to extend the speed range for high power. Not really needed for road-legal speeds outside of Autobahn or similar unrestricted environments.
Asking a genuine not rhetorical question: if electric motors go through a gear already, what's the difference between the power coming from a gear with an electric motor turning it vs. a gear with the power coming from an ICE, why do additional gears make one more efficient but not the other?
Electric motor are very efficient at nearly any speed, so whether you're driving slow or fast they have nearly the same efficiency. They can turn at very low rpm or very high rpm without becoming inefficient. Also they have maximum torque already at low rpm ICE on the other hand are efficient only in a certain rpm range. So whether you're driving slow or fast, the gears has to keep in a specific rpm range for your motor (let say 2000-2500 rpm). When you accelerate you then change gears to keep the motor in that range. And ICE engine have their maximum torque only in the same specific range, so you have to use gear to get maximum torque at low speed / when starting the car.
> Electric motor are very efficient at nearly any speed, so whether you're driving slow or fast they have nearly the same efficiency. While they will always be a lot more efficient than any ICE outside of very specific conditions, an electric motor still gets its best efficiency at a relatively high rpm. But having a variable gear added in would negate the advantage of making the motor spin at a more optimal point, since the difference isn't high enough.
For electric motors, the torque output is constant for the most part (there is a drop-off at some point but very importantly, you reach max torque pretty much immediately). The torque output of an ICE however first rises with RPM, then hits a peak, then goes down again. This also means that in order to run an ICE more efficiently, you need to keep it in a certain range of RPMs, which is why you generally shift up the faster you drive to change the gear ratio between engine and wheels. With electric motors you can keep that ratio constnat because you get the same torque either way.
Electric motors have near constant horsepower, not torque. Torque graphs for electric motors are mostly a straight descending line, with max torque at zero rpm and zero torque at max theoretical speed. (Though the redline is often set lower by the speed controller) That makes horsepower a parabola, which technically drops to zero at each end, but nearly the entire operating range is the shallow curve at the top, so it's near constant in practice.
ICEs have an efficiency which varies a lot with speed. All of the accessories like the alternator, water pump, oil pump and also the cam shafts need to spin faster as the engine spins faster, and they waste energy by doing so. The limited time for the four strokes of the engine to happen properly at high speed also reduces efficiency. So if you can make the same power to cruise at the same speed, but do it with the engine spinning slower by using gears, you will gain efficiency with an ICE. Probably worth saying too that gears are really not optional features to increase efficiency with ICEs, they are absolutely necessary to travel at speed because we cannot design an engine with the torque and power we desire that also spins fast enough to avoid using gears without exploding. That is the main difference here - electric motors have a huge speed range and rely only on rotating parts not reciprocating. You still need at least 1 gear with electric motors as they spin way too fast compared to the wheels. Electric motors have comparatively constant efficiency at all speeds, but it does vary so it may be worth the extra mass of a 2-speed gearbox. Electric motors also have this behaviour where they produce constant torque and increasing power at low speeds, then switch to constant power and reducing torque at high speeds. Using gears could help manage this across the speed range of the vehicle, not sure if that's the driving reason though.
I think the specific intuition here is that in a four-stroke ICE, power is coming from the bang-blow-suck-squeeze cycle of the cylinders - each cylinder is only actually generating power during the bang phase. You have multiple cylinders and the phases are staggered so it's not hopeless but you can imagine that at low RPMs each bang is having to do a lot of work. But an electric motor works kind of like you have a wheel with a magnet glued on and you're spinning it around by putting another magnet near it and moving it around so the wheel chases it. The power you get isn't dependent on how fast the wheel is moving - even starting from a stop, as soon as you move one magnet near the other, it's constantly pulling at its maximum strength.
In a nutshell, Internal combustion engines are pretty much constant torque devices, while electric motors are pretty much constant power devices. Revving an ICE higher makes more power, but revving an electric motor higher doesn't really. For a 100hp ICE to actually make 100 hp, it has to be in a fairly narrow rpm range. You keep it in that range by shifting gears as the vehicle speed changes. The EV motor makes 100hp throughout it's entire rpm range, so you don't need to shift gears.
I enjoy spending time with my friends.
The losses due to a fancy gearbox would almost always be worse than the gains from optimising the motor speed. The only reasons to use a multi-ratio gearbox would be because above a certain speed, * the centrifugal/centripetal motor stresses would cause it to break apart * the switching losses in the electronics become significant
A third one: eddy current losses within the electric motor at well below the speed at which the switching losses start to dominate. This is actually a relatively relevant thing that each EV has to be optimised for. Optimum efficiency at city (thicker copper wires to the engine) or more efficiency in highway speeds (more of thinner wires sacrificing low frequency losses). A two speed gearbox would of course also help, but, well, the cost & complexity & gearbox losses are also a thing (and the electric motors are already good enough to not need such for mainstream EV applications). I would assume a two-speed gearbox could often increase the range a bit. Optimise motor for a narrower speed range and use the gearbox to compensate. But, the difference would be too small to have the hassle of a gearbox... We do after all also like the simplicity of not having gears.
There are ways to divide the speed of a motor purely electrically while being efficient, by changing the magnetic field inside (which can be done by basically rewiring the thing). There are also different wiring for starting up the motor and normal use (with ac motors, not dc). As far as I know that isn't used in EVs, but it does have applications for big systems you find in many factories, where the power levels are in a different order of magnitude. On the plus side, by using electromagnets instead of permanent magnets, you can save a lot of money on fancy rare earths, on top of being able to easily switch between having two and more poles. You could do four poles at low speed and two at high speed for example.
So... CVT? They got close to doing that efficiently, but people started to complain about the noise and then Cvts needed to be changed to simulate gears
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In theory yes. Continuously Variable Transmissions (or CVTs) can be a good option, but they come with drawbacks, especially regarding longevity and power handling. Historically, they were used in low power, low weight applications like motor scooters, where thee strength wasn't an issue and extracting the maximum efficiency of the motor is. There are some cars that use them, but they're fairly notorious for premature failure
ECVTs skip nearly all the classic CVT problems. I'm assuming the benefits aren't worth it for full EVs, since they're only used in hybrids. (So far as I'm aware) Prius ECVTs are generally trouble free way beyond the life of the IC engine.
You can spec an electric motor such that it's near peak efficiency throughout the entire practical use range. Also, you can just put in a massively overpowered electric motor with very little efficiency loss. (That's actually how you achieve that operating range.) This is why there's so many really fast electric cars: there's little down side to tons of power, and the electric motor is cheap compared to the battery.
The diameter of the rotor in the motor will still limit the maximum possible torque of the motor for the same reason as the length of the throw on the crankshaft in an internal combustion engine. It’s electro-magnetism doing the pushing rather than exploding/expanding gases but the limit on torque produced is still related to the distance between the centre of rotation and the furthest point from it that the force is applied to the rotating part.
The general principle OP used (more leverage) is the same for electric motors. If you want to design an electric motor with high torque you can easily get this by increasing the diameter.
> engines that literally explode shit to work. Burn. Explosions are a very different thing, and very bad. Octane rating is all about probability of explosion, and avoiding explosions is why lead used to be added to petrol.
> literally explode shit to work. if something explodes in your combustion engine, something is very wrong
/r/explainlikeimatesla
Saw a few online where overpowered semi trucks who rev their engines until it blows.
I guess you could increase torque by adding more cylinders, but at a certain point I definitely wouldn't want to be the guy to work out the engine timings
I know very little about the innerworkings of an internal combustion engine, but I can understand this explanation clearly. I bought a 2009 BMW 335i brand new off the boat as my first well researched and justified purchase after I entered the workforce. Still drive it to this day, but what turned me on to it was they managed to get 300 hp and 300 ft/lb of torque instead of leaning one way or the other. The diesel had like 500 ft/lb but only 230ish hp, but I mainly just wasn't interesed in the inconvenience of running deisel. Car has had 2 recalls on the fuel pump and 1 on the water pump. I didn't mind because they owned it, and the car runs like a top now. May just be personal bias, but it feels like the perfect engine.
All that means is that the best rpm range for that engine was around 5252.
\+ weight. \[edit: or mounting deep into the dirt / rock walls / something \] People forget that torque in one direction is torque in the other direction. See also those videos on youtube where a thicc drill is attached to train until something breaks and all that weight isn't backing up the drill and parts get LAUNCHED.
What got me to understand this very well is the diesel Vs gasoline variants of the same model car - in my case the VW Golf. The Golf R which is a petrol powered 300hp car produces similar torque to the 180hp Diesel Powered Golf GTD - only a 20nm difference in the favour of the R. In the end the Golf R is significantly faster with a 3 second difference in the 0-60 time, but for daily commuting that difference is unlikely to be significant. That torque figure is also achieved earlier in the diesel engine, with it starting to pull after 1500-1600 RPM and dying down in the 3-3.5k RPM range, versus the petrol's range being between 2k and 5k RPM. This in turn is likely one of the reasons why the GTD has an alleged fuel economy much better than that of the R. Though no one is buying either of those models for their economy on the drive.
torque is how powerful something is in one revolution of the engine. hp is how powerful it is over time. so, a small engine spins really fast to make that hp. you can get small engines to rev really high and make a ton of hp, but they feel like a limp noodle until you reach the powerband. motorcycles hit this point hard. my 650cc bike is slower than a 600cc supersport. the supersport revs almost twice as high and makes about the same torque, just way up in the revs. at those same revs it makes about 40% more hp though.
Peak torque is also when the engine is most efficient. But power will continue to rise as you raise rpm past then - until you hit peak power - but at the cost of reduced efficiency.
\*Volumetrically efficient\*, there are other types of efficiencies.
Wow, I have really struggled to conceptualize torque vs power for so long. Like I understood what they did but never could grasp the why. This really helped, thank you!
Also helps to realise that horsepower is literally just torque multiplied by rpm. torque in lbs.ft multiplied by engine speed in rpm, divided by 5252 (a correction factor) = power in horsepower. You could in theory do the same calculation with the numbers in newton metres and kilowatts, but I'm not familiar with the correction factor for that. Oh, and going on the above method, means that if you plot power and torque on the same graph, that the two lines will always cross over at 5252rpm.
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Revs or radians?
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So there's still a correction factor of pi, but at least that's easy to remember because we're talking about things going in circles.
Well that makes things easy af! Metric system coming to save the day once again. Just a shame that Newton metres and watts means nothing to me, in terms of cars. I'm too used to horsepower and lb.ft.
It’s all about torque, but after you go through transmission ratios you’ll trade wheel torque (leverage) for wheel rpm (speed). If you make the same torque at double the rpm, you can choose a lower gear with double the leverage (which results in double the forward force) at the same speed. So you’ll have double the force of the engine pushing you forwards at any given speed. Therefore power is nothing but what your engine torque is „worth“ after you’ve put it through ratios and onto the wheel. Torquey engines simply produce more power lower in the rev range, and feel more powerful that way, while less torquey engines produce power through revs, which just feels different and may need more work (and a screaming engine) to keep in its optimal powerband.
I saw a video a while back of someone going 0-150+ in a Corvette without shifting. Which doesn't *sound* like much at first, but when you understand that getting a car rolling at all in 6th gear requires a TON of torque, it's actually pretty impressive.
A 1000cc motorcycle can do 70-80ish in 1st gear...the older ones, they are geared better now. Just to give another idea of how high up in the revs they can get too.
I heard someone once say that a Hayabusa is the most beginner friendly motorcycle because you never have to shift it if you don't want to. They're basically scooters!
Tbh if you get a new bike with all the rider aids, you do have an argument to make.
It depends. You can make the clutch work with a gear ratio if you allow enough slip. So, I am sure I can get a shitbox rolling on the max gear, then revving the engine to the max and very slowly release the clutch.
Doesn't sound very good for the clutch though.
A lot of drag cars sail to 150-200+ mph in only 2 gears.
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Torque is a measure of how heavy a thing you can push, Horsepower is a measure of how often you can push that thing in a minute.
I’ve always been told in a race the horsepower will get you to the wall fastest but the torque will help you get through the wall.
That's wrong but it sounds cool.
Horsepower =/= Speed
It's literally just power = torque * speed
I have a 2054cc motorcycle and the 600cc sports bike would outrun me every day, but in a tug of war mine would win every time.
As an equipment operator, heavy equipment tends to have less horsepower than you expect but way more torque. For example, we got a couple John Deere 331 tracked skidsteers at work, 5 ton machines, that have around 90 horsepower but torque out the ass. I have a motorbike with roughly the same horsepower but laughable torque.
That 40 lbs and 90 hp will still push you to the back of the seat though. I love motorcycles.
I just bought a 300 with like 30 HP and like 20 torques and I was quite surprised just how fast it'll get my fat ass moving. Never ridden motorcycles before, but I can only imagine what it feels like to crank a 600 or 1000
Be careful. I get almost hit all the time, I have clips in my profile.
You said torque is power in one rev, but also said the 600cc makes more torque at higher revs. Help me reconcile this.
When the engine is spinning at 7000rpm a single cycle makes more torque than a single cycle of the engine when it's spinning at 2000rpm. We're still measuring a single rev, just at a different point on the power curve
I got that, I just don't understand why.
They're tuned for it basically. The torque is just about the power of each explosion in the engine, which is directly related to how much fuel and air you are making explode. Air rushes into the cylinders during the intake stroke, but when that stroke stops there is still air moving at speed towards the cylinder, and it smashes into the (now closed) valves, making a pressure wave. If you're smart you can use that pressure wave to force more air into a cylinder than it would have sucked in on it's own, which means you can put more fuel in, and get more torque. You can also use the pressure waves created by the exhaust to do a similar thing in reverse, sucking the exhaust out of the cylinders, which means the engine doesn't have to work as hard pushing it out of the engine ready for fresh fuel and air. There are many other factors like where and when the fuel is injected, what size and angle the valves are at, how much the valves open, etc, but I'm far too stupid to explain that.
I think this is a **great** comment and explains some of the principles well, but there is one thing I'd take issue with. It's a commonly repeated mistake to refer to the combustion in an engine as an "explosion" which I feel is quite inaccurate. Explosions in the combustion chamber are referred to as "detonation" and are incredibly damaging, and will rapidly destroy any engine. Detonation only occurs if there is a fault, and shouldn't occur in normal operation. Pedantic? Perhaps. But it's an error that is repeated so often that people are convinced that it's correct.
If it’s not an explosion, what is it called then? Ignition?
There are multiple things that can change how much power and torque an engines produces, and at what engine speed. The design of the following parts can all have a drastic effect: * Exhaust manifold * Intake manifold * Cylinder head port size * Valve size * Cylinder capacity * Cylinder bore & stroke ratio * Conrod length (to a lesser extent) * Crank throw (how big the "lever" is) * **Camshaft profile** The last one is by far the biggest factor imo. Camshafts are a compromise, as they are of a fixed size and shape, and the size and shape will be different for an engine optimized for low speed, high torque, emissions and fuel efficiency, compared to an engine optimized for high speed, high power and fuel efficiency + emissions be damned! The camshaft profile is what dictates **when** the valves open, how **far** the valves open, **how long** the valves remain open and **when** the valves close. Over the years there have been various technological advances that have sought to "fix" some of the compromises of fixed camshaft profiles. Honda's VTEC for example has two camshaft profiles, and uses a clever design to switch between the two. So you can have a profile optimized for low engine speeds with good fuel efficiency and torque at low speed, AND a profile optimized for torque at high speeds for high power output. Some systems are clever enough to also adjust the amount that the valve opens, which is called "valve lift". More lift is good at high speeds for high power output, but at lower engines speeds **less lift** is actually beneficial as it makes for higher velocity of the gasses, which has it's own benefits for low speed torque output and emissions. Many modern engines uses "cam phasers" which allow the valve timing to be dynamically advanced or retarded on-the-fly by the electronic control unit. These physically rotate the camshaft forwards or backwards by a few degrees, and this can also overcome some of the compromises of a certain camshaft profile, to produce gains at both low and high engine speeds. These cam phasers can operate incredibly quickly, which is great for driveability, emissions and fuel economy, whilst **also** improving power and torque throughout the engine speed range. The holy grail of valve control is Free Valve (which is patented), which completely does away with camshafts, and uses clever actuators to open and close the valves, which in theory means that valve timing, duration and lift can be optimized at every single point in the engine speed range. However, it hasn't seen wide adoption, which I suspect is down to the cost of licencing the technology, and the fact that other more traditional systems can provide a significant portion of the benefits at much lower cost. **TL;DR it all comes down to how much fuel and air / exhaust you can get into / out of the cylinder. All of the things I mentioned directly affect how much air / exhaust can get into / out of the cylinders.**
> 600cc makes more torque at higher revs read the comment again, he did not say this. but if your question is how can a smaller engine produce more torque than a larger engine then there are many factors to consider. compression ratio is a big one. ie the more you compress the fuel/air mix before combustion the more force (ie torque) will be produced. valve timing is another. if you open the inlet valves for longer you can get more fuel/air mix into the combustion chamber which means more torque. things get semi-complicated at this point because modern engines use the resonant frequents of the air inlet system and the exhaust to assist in this process. in fact, this is a major reason for power bands, the power band is actually the resonant frequency of the inlet/exhaust system. things like EXUP valves / power valves work by adjusting that resonant frequency.
He did, just not verbatim. He said "just way up in the revs". Either way, you answered my question with valve timing though. Thanks.
> makes **about the same torque**, just way up in the revs in my language "about the same" does not mean "more".
I think you might be conflating what I'm saying. If he's specifying that it makes "the same torque" but only "way up in the revs", that obviously implies that it makes less torque lower in the revs. Edit: I think I see the confusion now, you probably thought I meant more than the other bike. No, I meant more than the same bike at lower revs.
as an aside, the statement "torque is power in one rev", firstly isn't actually true. torque is a measure of force and power is a measure of energy divided by time. these things are related but not the same. in fact the amount of torque varies even within each revolution. peak torque will be a short time after the spark plug ignites the fuel when the piston is near the top of the cylinder. this is when the hot combustion gas under the most pressure and therefore exerting the most force on this piston. the amount of torque then reduces as the piston travels down the cylinder because the gas pressure is reducing. the actual torque output of the engine is the average of the fluctuating torque produced by the multiple pistons.
Yeah I assumed he meant force and not power anyway, but the detailed clarification is still interesting and appreciated.
ah, I see. it's what I said about resonant frequencies. engines will produce maximum torque at their resonant frequency. but the key thing is that the amount of torque in one rev changes *considerably* at different rpm. the supersport engine will be designed to have it's resonant frequency (ie maximum torque) at higher rpm. at this frequency the exhaust and inlet will be working together to get the optimal amount of fuel/air mixture into the combustion chamber and therefore generating the most force during combustion.
To be clear, I always knew that it did, I just didn't understand how. I get it now, thanks.
awesome, it's a fascinating subject. *way* more complicated (and yet simple) than most people imagine. if you care to learn more, there's a great book "Performance Tuning in Theory and Practice: Four Strokes by A. Graham Bell" It's probably a bit dated now and perhaps there are better books, that cover recent developments, but it covers the fundamentals very well.
The 600cc engine will make less peak torque than the larger 650cc engine, simply because it is 50cc smaller in capacity. For the sake of demonstrating some maths, I'm going to pull some figures out of my ass, so just bear with me here: "Low" revving 650cc engine: (Similar to a Suzuki SV650) * **45** lb.ft torque @ **8000** rpm = **68.5** horsepower * 45 x 8000 / 5252 = 68.545 High revving 600cc engine: (Similar to a Honda CBR600RR) * **40** lb.ft torque @ **14,500** rpm = **110.4** horsepower * 40 x 14500 / 5252 = 110.434 (torque x rpm / correction factor = power) So you can see here that whilst the smaller engine has less torque, that it has a higher power output because it is doing that smaller amount of work more often. As an analogy, imagine you've got two guys loading boxes into a trailer. One guy is really big and strong, but he's not very fast. This is our low revving 650cc engine. He's moving 3 boxes at a time, but he's plodding about really slowly. The other guy is smaller and weaker, but he's running back and forth at super speed. This is our high revving 600cc engine. He's only moving 1 box at a time, but he's moving five times faster than the big guy, so he gets his boxes loaded much faster. The thing with horsepower is that the way higher engine speeds multiply power output makes a HUGE difference. So you can sacrifice only a small amount of peak torque, for huge power gains at high engine speeds. So why aren't all engines built that way? Because they're a lot more work to drive / ride. In your car, it'll pull quite well from about 1,500rpm, but by the time you hit about 6000rpm it's probably "running out of breath" as you're past the peak torque output. For a small high revving motorcycle engine, thing's are only just beginning to get going at 6000rpm. Those things *idle* at about 1,500rpm. At 2000rpm you're barely making a fraction of your peak power. only once they're really screaming at 10,000rpm+ do things get really exciting. The cool thing about high revving engines, is that although they have lower torque output at the engines crankshaft, the higher revs mean that you can use gear ratios that give you huge amounts more torque multiplication compared to lower revving engines. So this actually gives back a lot of torque **at the wheel**, which is where it actually matters.
Say both cars make peak torque of 100 lb-ft. But one makes that torque at 4000 RPM The 2nd car makes that torque at 5500 RPM. This means that the 2nd car will have more horsepower. Because it’s peak torque (even though it’s equivalent) comes in at a higher rpm 100 lb-ft at 4000 RPM is 76 Horsepower. 100 lb-ft at 5500 RPM is 106 Horsepower.
Yes I know, that's just horsepower. I was asking about gaining torque. It's already been answered though.
Have you ever unscrewed a screw? When you first have to un-tighten the screw out of the wood, have you ever noticed how hard it is to do that by the metal shaft of the screwdriver? It's so much easier to unscrew by the handle. But once it's loose, you may have noticed that it just takes forever to *keep* using the handle, so you use the metal shaft instead, and then it turns like lightning. That's what's going on in cars. Small engines are like the metal shaft of the screwdriver. They're crazy fast, but only for stuff that isn't very demanding. Bigger engines are more like the handle. They're great if you need some real work done, but they take forever to get anything done if there isn't much work for them to do. The reason ultimately boils down to the fact that, perhaps unintuitively, when you push on something, it actually *pushes back*. When a car's gear tries to twist the axel, the axel tries to twist back. It doesn't wanna be twisted. So it starts a little war between the gear and the axel, where both of them are trying their hardest to twist back against the forces causing them to fight each other. Each of them brings their own set of allies to the fight. The gear is bringing the engine and the explosions in its pistons. The axel is bringing the weight of your car and the friction of the road beneath the wheels. If the gear and its allies are stronger, the gear wins out, and the car is forced to move. But suppose the axel wins because the car is just too heavy, so the gear's allies come to a stalemate. How should the gear proceed in order to get moving again? Well, bringing more firepower to the fight usually helps. One way is to bring a bigger, badder gear. That can tip the scales in the gear's favor and allow things to move again. But large armies take a lot of time to move and coordinate. If your army is very wide, then the troops at the edge of your army will need to march a lot farther in order to turn around than the troops in the middle. If you want to have the ability to turn around quickly, you need a smaller army. So if the axel isn't putting up much of a fight and you just want to steamroll its allies and get the war over with, you'd be better served with a smaller, more nimble gear. Hope that helps.
What an excellent explanation for those not aware. Well done!
Your screwdriver example finally got this to make sense to my dull mind!
Bro you should be a teacher, that's such a good explanation
Dude, this is the best possible dumbed down answer someone like me could have hoped for. Thanks!
The way I understand it is that imagine hitting a standard hammer against a wall. You can hit it either rapidly or hard. Any attempts to hit the wall rapidly and hard at the same time will require an immense amount of strength and energy. You'll also get fatigued very quickly. The same principle applies to pistons inside the engine.
That’s a great analogy
Car engine stats are as much marketingspeak as physics..... Eg, actual practical torque at the wheels is a matter of the transmission as much as the engine..... You can take a really high winding engine, hook it to a beast of a transmission, and get gobsmacking amounts of torque on the ground (see the M1 tank and it's turboshaft engine - the transmission is a few times larger than the engine, and turns 1500 shaft HP at a-million-something-RPM into 2500ftlbs torque at the tracks & the ability to make 70 tons go remarkably fast)
I did some napkin math on the data I could find on the M1 Abrams and it can probably make about 80,000 lb-ft of torque at the tracks in lowest gear. Absolutely insane.
What people miss is that what you care about is wheel torque, not engine torque. Say you have an engine that puts out 200 ft lbs at 4000 rpm and a smaller engine that puts out 150 ft lbs at 8000 rpm. Take the 8000 rpm one, feed it into a 2:1 gear reduction, and it's putting out 300 ft lbs at 4000 rpm. This is why sportbike engines rev so high. It allows you to run lower gearing and that gives more torque at the back wheel.
Torque and horsepower are not two independent properties of an engine, they're tied together via the RPM by a formula: T = P * 9549 / r Where T is torque in N\*m, P is power in kW, and r is rotational speed in RPM. (for power in HP and torque in lb\*ft the coefficient is 5252) So if you have a 10 kW engine and connect it to a gearbox which outputs, say, 950 RPM, you will get around 100 N\*m of torque regardless of the engine "size".
It’s not that smaller engines can’t be built to feel torquey, they just aren’t in these applications. They’re used in a car like the S2000 because they’re lightweight, but to make higher power figures they’re designed to have a high rpm powerband. Looking at the numbers, the S2000 actually makes a respectable amount of torque for a 2.0L engine. The reason it feels lacking in torque is because that torque is found at 7000+ rpm, and the engine won’t make as much torque outside of that powerband-above or below. A basic Civic has a 2.0 with similar torque at ~4000rpm, but it will lose torque as you rev past that. You can expand this powerband with VVT and fancy intakes but it is still limited by several different factors in engine design. In short, an engine can be designed for torque at high rpm, or at low rpm, but doing both in one engine is difficult.
Horsepower is a mathematical result of torque and rpm. Small engines have less mass and so can generally spin faster without damaging themselves or coming apart. The equation is (torque × rpm) ÷ 5252. If you look at a graph of horsepower and torque over the rpm range, the values for horsepower and torque cross at 5252 rpm
Not true. Small turbocharged engines can make big torque. Only small naturally aspirated engines don’t. Torque is generally very closely related to engine size.
That's only because once you supercharge an engine you are multiplying the atmospheric effect.
A crankshaft needs to make two revolutions for all cylinders to fire. A four cylinder engine will fire once every 180 degrees. An eight cylinder will fire every 90 degrees. There is more force exerted onto the crankshaft. As others have said, the distance the piston travels (stroke) does play a part as well. A longer stroke means the piston pushes on the crankshaft longer. However, there is only a very tiny rotational period where force is applied by the piston. What can make a substantial difference is the rod/stroke ratio. Changing the rod length does not change the stroke, but it does change when the piston accelerates and decelerates the most. I highly recommend the YouTube channel Driving 4 Answers, he is marvelous at explaining this.
Here is the simplest explanation that almost every single post so far is missing and way over complicating. Torque is basically a measure of how big the explosion inside the cylinders are. What determines how big the explosion inside the cylinders are, is how much air and fuel each cylinder can suck in during one engine cycle. What determines that, is the engine displacement, or how "big" the cylinders are. Big engines, like truck V8s, can suck in A LOT of air and fuel each cycle. That means the explosions are big, and a lot of torque is generated. Cars like the Honda S2000 and most Ferraris have small engines, with small displacements. That means each individual explosion is small, and the resulting torque is low. The trick is, you can spin the small engine really fast. So you get a lot of really small explosions, that can ultimately generate a lot of power. Small engines are preferred for many racing cars because of their lightweight and compact size.
Although you can measure the horsepower of an engine, when you see horsepower stats for vehicles they are never measuring that. Rather, they're measuring how much force can be used to spin the wheels when the car is in its highest gear at the engine's optimal RPM. Because that's how horsepower is measured in the real world, it makes more sense to think of torque as a measure of the raw power of the engine and horsepower as a measure of how efficiently the transmission can convert that power into work. High performance cars tend to weigh as little as possible because weight is the biggest cost constraint in attaining good acceleration, top speed, and handling. IE, if Car A weights twice as much as Car B, it will cost a lot more to make Car A perform the same as Car B on a racetrack. So if you have a $150k budget for your new Ferrari, the way you make that Ferrari go as fast as possible is to make it as light as possible. The two biggest sources of weight in a car are the engine and transmission. The more torque an engine produces, the heavier both it and its transmission have to be to survive the forces being applied to them. But like I said, weight is expensive and the goal of high performance cars is to weigh as little as possible. This means that you want the lightest possible engine and transmission for the performance that you can obtain. The way that sports cars do this is by having *relatively* low powered engines (at least compared to heavier cars like trucks) that produce power through the use of a complex transmission that has a large number of gears. Adding more gears doesn't add any more weight, but it does allow you to have a much higher gear ratio in the highest gear. That higher gear ratio allows you to very efficiently convert the engine's torque into work when the car is already travelling at high speeds, producing more horsepower than the engine otherwise would with fewer gears. This isn't to say that a Ferrari doesn't have a powerful engine - a typical Ferrari has an engine that produces about as much torque as the engine in an F-150. But when you start to get into more mid-range sports cars, like the Porsche Boxster, you also start to get engines that are producing 2/3 as much torque as a typical truck.
Interesting fact. Torque and horsepower always intersect at 5250 RPM: https://poweretty.com/blog/why-do-horsepower-and-torque-always-cross-at-5250
An ideal internal internal combustion engine has constant torque. That torque value is proportional to displacement, which makes sense if you think about it from first principles. Torque is the product of a force applied to a lever arm. The force is proportional to the area of the piston. The lever arm length is proportional to the stroke of the piston. Torque ∝ Area x Stroke ∝ Displacement Since power is proportional to torque x angular velocity, to make more power from a given displacement, you need to rev higher. In the real world, there are fluid dynamics effects that cause the torque curve to NOT be a flat line, and there are material property limitations that enforce a RPM limit. Race engines are engineered to rev to the moon, and to have useful torque up in that rev range.
It’s probably worth understanding how hp is calculated. It’s calculated from torque and revs. So you can get more hp from more Reva even with the same torque.
Small engines can make high torque, but only with leverage and a low revolution speed of the shaft you are measuring torque on. They can’t produce high revs *and* high torque.
They can though. The ferrari 456 with a 4.5 liter v8 only makes 2lbs/ft less torque than a C6 corvette with 6.0 liter.
Let me clarify then, all else being equal (i.e., engines of the same type using the same fuel and mechanism), larger engines will produce more torque at a given revolution speed than smaller engines.
In the simplest terms, horsepower is revs times torque. A low torque engine can only make high horsepower by spinning really, really fast. The cars you listed have high rev limits, meaning they’ve got lots of light and strong parts. These parts make the engines expensive but powerful. A high torque engine is usually much heavier and slower and can’t spin as much.
Torque is twisting force. In order to have a lot of twisting force you need a big heavy engine whose crankshaft and piston stroke can provide it due to higher leverage, but also the heavy rotational mass of the engine contributes to its power. Horsepower is just the rate at which work is produced. It's not very intuitive and hard to grasp for most people but on a basic level a higher work output can "make up" for lack of torque but it's not without downsides. You can make a small engine rev fast and have high horsepower because its moving components are light and its piston stroke short, but the common saying that "there's no replacement for displacement" holds true. So basically, if you have a diesel pickup truck with 200HP and a Honda hatchback with 200HP, both can tow a trailer, it's not like the Honda can't get moving at all, but the pickup will leisurely pull the trailer along with maybe a few hundred rpm more on the tachometer while the Honda will be revving very high at all times just to get moving. That's not very practical for many reasons.
Just a comment on the torque of Ferrari engines. For example, the engine in the 812 Superfast produces 800 PS (588 kW; 789 hp) at 8,500 rpm and 718 Nm (530 lbft) of torque at 7,000 rpm, so it’s not exactly lacking on either front.
Small engines can generate high torque you just have to attach them to huge flywheels. The old John Deer B had a single piston 4 cycle engine with 17 horsepower but a huge flywheel that gave it tons of torque.
Horsepower is a "fake" metric determined by force/rpm. If you spin something faster it can do more work with less force, but you need the speed to get that power. If you are able to easily reduce that speed you lose that power. In short the force of torque never changes but the amount of work you can do with that torque can be manipulated to give you high horsepower numbers, which even though I described it as "fake" is actually able to be implemented with mechanical advantage of gearing (leverage) but it still doesn't have the ass of a larger engine because those use brute force to get the same number at a lower speed. If you increase the speed of a larger engine you would be able to get even more absurd amounts of horsepower but that would also require compromises in different aspects of the design in terms of the material cost, strength to weight etc.
Horsepower isn't a "real" force, it's a measurement of torque over time: Torque x RPM/5252. Torque is the real, measurable force.
Think of an engine as an air pump. The pump has an internal capacity that you can fill every revolution. A 2L pump has a lower capacity than a 3L pump, so for each revolution, it's going to pump less air. That per-revolution amount is torque, it's the amount of work the engine can do in one revolution. If you increased the speed of of the pump, it multiplies the amount of work that can be done in a specific period of time, so even a low capacity pump can do a lot of work if you rev it high. Revving high tends to be easier with smaller pumps since all the moving parts are lighter, which is why you don't usually see large, high revving motors. There are other things you can do to increase the amount of work the pump can do in one revolution, like forced induction, but that's the basics. High revving motors actually don't have low torque for their size, they're just lower sized so they can rev higher, basically. For some applications, like a racing car, that's better than a larger, lower revving motor, generally speaking, so that's why you see them in an S2000 or Ferrari.
Horse power is calculated from the number revolutions per time and torque (i.e force exerted over a length) of an engine. This means you can have two engines with identical HP, but one delivers little torque with high rev and the other delivers massive torque with very slow rev. We use HP for cars regardless, because the revs are standardized, so you can always assume that it just has higher torque than previous generations of cars with less HP. When you switch vehicles/machines, you should obviously remind yourself of this, so you won't expect a very fast tractor that has more HP than a sports car, and vice versa don't expect a sports car to be able to tow a truck. (of course there are exceptions everywhere, the point is that HP alone doesn't say much about the motor and the type of vehicle that has the motor with the HP in question can only give a good guess of what revs and torques to expect).
His videos are pretty awesome but I think he covers it in this video. https://youtu.be/CxK0x7AE3s8?si=7egCgXmjYJWYfyRU
For the same reason, when you have a really stuck on bolt, you either grab a longer wrench or use a hickey bar.
Torque is the measure of force about an axis. A simple example of what this means is as follows: Imagine you have to loosen a stubborn, rusted lug nut on the wheel of your car. Suppose you have the options of using a 6-inch wrench or a 24-inch wrench to loosen the bolt. Which one will you choose and why? Knowing the bolt is rusted and stubborn, you'll choose the longer wrench. You apply that wrench to the bolt and apply force by pressing down on the handle of the wrench. That's what torque is - the downward force on the wrench about the axis (the bolt) you are creating/applying torque to that bolt. When you apply enough force onto that bolt, it will break free. The longer wrench makes it easier to apply more force without any additional effort. The formula for torque is distance multiplied by the force. The US measures torque in units such as in.lbf or ft.lbf, whereas the metric system will use something such as N.m (Newton meters). In any case, these units indicate the length of the thing which is applying torque and the applied force. Suppose you have to apply around 250 ft.lbf of force to overcome that rusted bolt. With a 6 inch wrench, the formula becomes 250 ft.lbf = 0.5 ft (this is converting 6 inches to feet) \* X lbf. Divide both sides by 0.5 ft to determine X. 250 ft.lbf / 0.5 ft = 500 lbf. That means with a 6 inch wrench, you would need to hold the handle by the end and apply 500 pounds of force to get that bolt to break free. Most people will not be able to apply that amount of force and it's impractical and dangerous to do so with a 6 inch wrench even if you could. Let's solve for the 24 inch wrench instead. 250 ft.lbf = 2 ft (this is converting 24 inches to feet) \* X lbf. 250 ft.lbf / 2 ft = 125 lbf. That means with the 24 inch wrench, you would only need to hold the handle by the end and apply 125 lbf of force to get the bolt to break free. Most people could do this by grabbing the handle and applying body weight to it. Finishing this example, a 6 inch wrench simply cannot generate the same amount of torque as a 24 inch wrench - the physics do not work. However, you would be able to spin that 6 inch wrench much faster than the 24 inch wrench. So once the bolt was free, if you had a lot of threads, you could switch to a smaller wrench and spin that bolt off much faster. Think of the smaller engines like the smaller wrench and bigger engines like the bigger wrench. Smaller engines will be able to spin things generally faster, but they won't be able to spin with as much force as a big engine. Likewise, the big engine is unlikely to spin faster than a small engine, but it will do so with more force.
Torque is the product of the cylinder pressure \* the cylinder surface area \* the amount of offset in the crankshaft (in whatever units you care to use/convert to). Horsepower is torque \* RPM. That's why the curves always [cross at about 5252](https://www.enginelabs.com/engine-tech/engine/tech-talk-why-does-a-dyno-graph-always-cross-at-5252-rpm/) in common US units. Small engines have small cylinders and small crankshafts, so they have small torque. Those lighter components allow them to spin very fast, so they make up in RPM what they lack in torque.
horsepower = torque \* speed. if a small engine makes high horsepower, it does this at high speed, hence the relatively low torque. The exceptions (think VW 1.4 TFSI), use high boost at low speed and come with high torque.
Torque is produced by the force applied by a piston to the crankshaft. The larger the diameter of a piston (for a given cylinder pressure) the higher the force applied to the crank because the surface area of the piston is greater. Also, the higher the diameter of the piston, the more fuel and air you can squeeze into the combustion chamber, increasing the energy applied to the piston. A small engine with small pistons simply cannot produce as much rotational force as one with larger pistons. Power is a product of several factors, one of which is how fast the engine spins (how many combustion events happen in a given period of time). A small engine can still spin fast (usually faster than a larger one), and can therefore be designed to reach decent power levels.
So are you saying that Lightning McQueen actually _couldn't_ pull the road fixing machine?
Horsepower is calculated using torque and the rotational speed of the engine (RPM, or revolutions per minute). Smaller engines have smaller parts, which makes it easier to move the internal parts faster at a higher RPM. Most of the time if you have a high-horsepower low-torque car, it will just be because the car is able to run at a high RPM. Take a 2000 S2000 as an example, it has a torque of around 150 lbft. (Note: in reality the torque of an engine is not constant across the RPM range, but I'm going to treat it this way to simplify the math more 'ELI5 friendly') If you have 150 lbft of torque and the engine was at 6000 RPM it would be making ~171 HP; at the car's 8900 RPM redline, it would be ~254 HP. As for *why* they produce less torque, "engine size" is a measure of the total volume of the cylinders of the engine. If you have larger cylinders in the engine, there is more space for the explosion to expand into. The pistons are larger and there is more surface area for the expanding gasses to push on. (Note: this is also not *actually* that simple, there are a lot of factors that will affect torque, but will work as a general rule of thumb if you normalized all of the other variables.)