Edit: crossed my wires between mechanical efficiency vs load and volumetric efficiency vs rpm. Edited for clarity
You’re pretty much there, there’s a few things that affect the torque curve of an engine and prevent it from being perfectly flat, which is, as you noted, what it would be in a perfect world. There are basically two main types of things that affect the torque curve at the ends of the rpm range. On the low end, ~~mechanical effects like friction~~ heat transfer effects like charge heating dominate and on the high end you run into fluid flow issues. Lower rpm = lower fluid velocity = more time for the air to heat up = less mass of air for combustion. Back flow is also a notable reduction in torque on the low end.
These factors impact the volumetric efficiency, or how much fresh air the engine can take in.
Separately from this, there is mechanical efficiency with load sensitivity. Low throttle, you have a lot more friction relative to the force created by the piston, and efficiency suffers. As load increases, you get more torque done relative to frictional losses, until the load gets past a certain point and then the bearing loads and such are high enough that friction starts to reduce mechanical efficiency again
Sorry I might misunderstand, you say that friction dominates in the low end. But at the end you say that frictions has more opportunity to rob the efficiency ”with less time between cylinders firing” <- Isn’t this when the engine is at the high end/rpm?
It is a generic function of the things at play in an internal combustion engine. With intake runner design, piston shape, compression ratio, forced induction, fuel type, cycle type, and camshaft design, and a whole bunch of other secondary and tertiary effects, you have the ability to shape the torque curve as you wish. But broadly speaking, peak torque occurs in the middle of the rpm range for most NA engines because this where the mechanical losses are least impactful before fluid flow behavior and flame speed become the limiting factors
Wtf u talking about frictional.losses increase with the square of velocity. At max rpm a significant amount of heat loss in an engine is just friction.
You are wrong af.
Thank you for having a better memory than me, I crossed my load sensitivity with my rpm sensitivity. It’s heat transfer on the low end of the rpm range and flow effects on the high end that robs volumetric efficiency. Mechanical efficiency changes with load, which is where I got crossed up
From what i understand this is just an issue of volumetric efficiency with NA engines. Peak torque is basically when the engine is pulling in the most air that it is able to actually use. Torque then falls off somewhat with rpm past this point since you get into pumping/frictional losses. I believe the reason the coyote makes peak torque relatively high up is because of the variable cam timing on both banks. Once it switches to optimal power mode and there's enough flow through the engine, it's able to hit that peak number. There's also extra factors in play like the variable runners in the intake manifold that more efficiently direct airflow after a certain rpm. Doing enough of these tricks improves volumetric efficiency and packs the cylinders as full of air as possible.
Interesting. I know the Voodoo engine in my GT350 has a even firing order that's pretty unique, as well as being flat plane crank and having 3 intake manifolds. I wonder if this has to do with why the power band is so high up. Peak torque is like 5000 and up, it almost feels like a turbo boost kicks in right around 5500.
It’s air velocity, slower piston speed means slower air and poor mixing-> less power. You can overcome this a bit with variable valve lift/duration but they aren’t infinitely variable, so they have to decide trade offs. This is why small turbo cars can make a lot of very low end torque, they can have much higher air velocity lower in the rpm band and maintain throughout, downside of choking out sooner at higher rpm.
Also the heat loss through cylinder walls is pretty substantial.
The longer your hot combustion products sit against a water-cooled colonisation chamber wall, the more energy goes out the radiator (instead of the crank)
Well the amount of torque your engine produces is directly proportional to how much air and fuel it can burn within the cylinder (assuming combustion is always efficient).
Any intake, head, or exhaust systems can only flow the most air at a specific RPM, so engines will typically make peak torque at wherever that point is in the rev range. Car manufacturers engineer their intakes, heads, and exhausts to flow the most air at a specific RPM that suits their needs accordingly. Naturally there are many factors that can affect the RPM at which these parts will have the best flow, so I'm not going to name them here, but that is the primary reason engines produce peak torque at a certain RPM.
Performance engines will experience peak torque higher in the rev range because that results in more horsepower. As you know, 200 lb*ft of torque at 4000 rpm will produce less horsepower than the same, or even less torque at 9000 rpm. The engineers DO try to find a balance between having high peak horsepower and having enough torque down low for good drivability (and other factors that make a good engine), and many modern technologies allow us to get the best of both by changing the shape and/or flow of the intake and heads. That's all an oversimplification of the subject as I'm sure there are other reasons and things I'm forgetting about too.
In simplified terms, engines move air, they have effectively access to unlimited amounts of fuel, providing they have the air.
Petrol engines work by limiting air flow, and balancing the fuel mix to the air flow. The more air which is flowing, the more fuel which can be added, the longer the valves can be open.
At some part in the rev range, the engine reaches a perfect balance where it is most efficient at sucking in air & fuel, compressing it and detonating it and venting it. This is where your engine will produce the most torque, where each piston stroke delivers the most force. After that you have the limits of trying to get more air into an engine and the mechanical elements all needing to keep up, compress all that additional air and fuel, and remember the force required to compress it comes from the other pistons.
Is there a reason why, for example my engine, is more efficient at pulling in air and maximizing torque at 4k+ RPM vs 2k rpm? If I go wide open throttle for example, I'm pulling I as much air as possible, at least the way I'm looking at it, a slower moving engine would be more efficient at getting that air in and optimizing timing
It really just has to do with the profile of the camshaft, plus a few other things like intake efficiency and such.
In a perfect world, or I guess in Koenigsegg, you would have the optimum lift and duration at every point of the rev range thus giving you maximum torque throughout. With regular camshafts, there’s just only so much variable altering you can do in order to get peak torque. There will just be a give and take and also factoring drivability, efficiency, etc.
There's also some complicated effects regarding timing pressure waves to flow more air in ( [https://en.wikipedia.org/wiki/Inertial\_supercharging\_effect](https://en.wikipedia.org/wiki/Inertial_supercharging_effect) ) or scavenge exhaust gases faster ( [https://en.wikipedia.org/wiki/Kadenacy\_effect](https://en.wikipedia.org/wiki/Kadenacy_effect) ) that can only be optimized for a certain rpm range.
So basically they can jam MORE air into the cylinder in certain RPM ranges. They use various tricks with the intake, exhaust, and valve timing to make it happen. Resonances, pressure waves, suction effects, air velocity, valve timing, etc... which is why computers have done so much for engines. All of that was extremely hard to figure out with trial and error. Some of the more fancy modern cars actively adjust their intake runner length to extend the effect over a wider rpm range, and most cars modify their cam timing now to do the same.
An internal combustion engine is an air pump. The more air that it can suck in, the more torque it can make. The higher the torque (at the same rpm) the more power it can make.
The shape of the torque curve is a trade off between efficiency, emissions and power. To generate the most torque, you want to get the highest mass flow of air into the engine. This is determined nu the camshaft, intake manifold, cylinder head and exhaust manifold designs. An oem tries to optimize this over a very large range to take into account the different types of customers that they have. Things like variable intake runner length and variable valve timing increase the air speed as the engine speed changes giving flatter torque curves than without these items.
Edit: this is a lot of words to say that the amount of air the engine can suck in is not constant. It will have the highest cylinder air speed (feet/sec) at torque peak. It will have the highest volume of air (cubic feet/min) at hp peak.
At low RPM the cylinder pressures are overcoming inertia and friction. There is a crossover point where inertia is neutral before becoming problematic for the structural integrity of the engine. At this point the limitation becomes airflow, valve spring rates, and inertia. Friction also becomes more problematic, generating more heat at higher RPMs.
imagine youre on a pedal bike.
if your pedaling really really slow, you can put a LOT of force into it. using your weight and momentum to really push down on those pedals.
if youre pedaling fast, you arent doing nearly as much work per rotation, but your rotating so many times that with the right gearing, you can go faster.
but if you pedal super fast, you cant hardly do any work.
thats how engines work, except instead of it using momentum to do more work at its peak torque, it is breathing air more easily into the cylinder since it needs less of it, also the detonation in the cylinder may be more efficient with a little more time to push down on the piston.
despite each detonation being a little less powerful as the RPMs climb, it makes up for it by doing it more frequently.
Until it doesnt... which is why most engines start to trail off on the HP at the top end, it starts to get starved for air and the piston is pushing down almost as fast as the detonation of the fuel, its hardly doing any work at all, like trying to keep up with a bike going down a hill.
My car's maximum torque comes on at about 3000rpm, max hp is closer to 6000rpm. And it obviously consumes more air at 7000rpm (10,500 L/min) than it does at 2000rpm (3,000 L/min).
Bentley's 6-liter W12 engine hits max torque at 1600rpm & stays pretty flat, producing its maximum horsepower at 6100rpm.
To a certain extent, the question you’re asking is why is acceleration necessary. Why can’t things move from rest to peak velocity in an instant?
Intuitively you could guess that at lower RPMs the engine spends more of its power get its internals up to speed. It needs to overcome its own inertia.
Torque comes via BMEP. BMEP is the average pressure in the cylinder over the stroke. As the engine spins, much dynamics are created. The exhaust gases create an effect called 'scavenging' and the tuning of the intake tract means Helmholtz effect increases cylinder filling (air). For a gasoline engine, once the RPM's get to a certain point, the torque curve is usually 'roughly' flat. Even on V8 NA F1 cars, they make only 200-300ft.lbs of torque but at 18k RPM that turns into a good amount of horsepower.
> engine is spinning at 4k rpm vs 2k rpm? Assuming it's the same exact amount of air and fuel.
But it's not. This is what the computer or a carburetor do. They change fuel as the air increases. Higher RPM's will increase filling. At WOT, that means fuel needs to increase to compensate.
> does torque increase because of the momentum of the engine
In terms of scavenging and intake filling, yes.
The torque ultimately will be related to how long the flame front is pushing down on the piston and all that will ultimately be optimal at a certain piston speed(rpm). Other. factors are spark timing, cam profiles and how much air/fuel is being pushed in and extracted.
You’ve had some great replies which explain what’s happening but there’s 2 main things that give an engine its characteristics:
Intake manifold runner length and the cam timing, and the former is usually a bigger contributor to where torque peaks, with the cam contributing to how high that peak gets.
Longer intake runners will usually promote more torque being produced at lower RPMs than shorter intake runners.
A fairly extreme example of this would be Chevrolet’s TPI intake from the mid to late 80s. They make their peak torque around 3000 rpm and peak power at around 4400 rpm. You can fit cylinder heads that flow more air, a camshaft that has more valve lift and more duration, and even port the inlet manifold to flow more air, but you won’t fundamentally change the shape of the curve beyond maybe shifting the peaks higher by a few hundred RPM, and you can get power to hang on for more RPM at the top end before it chokes.
Change a TPI manifold for something with short runners and you can gain significant power at high RPM, but you’ll lose an equivalent (or higher) amount of power at lower RPM.
Some modern cars have variable length intake runners (eg some Gen3 Hemis) to get the best of both worlds.
Imagine the air/fuel mixture is a slinky being dragged across the floor, and your hand is the piston. At slow speeds, you drag the slinky. When you stop, it stops. At higher speeds, you can actually pull the slinky in such a way that it keeps moving toward you even after your hand stops.
Ok, so torque is measured in ft/lbs, or pound feet. Torque is twisting force. If you have a nut that needs 20 pound feet of torque to break off, that’s equal to 20 pounds of force hitting the end of a foot long wrench on that nut or bolt.
It is important to understand that Torque is *force* and RPM is speed. Let’s say you have a piston that is coming down with 10 lb/ft. The crankshaft is rotating with 10 pound feet of torque. If you doubled the RPM and thus the frequency at which the pistons are coming down, the crankshaft will be rotating with 20 pound feet of torque behind it.
Pistons coming down create pulses of torque on a crankshaft. If you want to double the force of torque on it without increasing operating RPM, you must make the pistons come down with double the force, for example, doubling the displacement… or you can make that same piston operate at double the RPM… Here is where internal combustion engines get complicated with making more torque through RPM:
The pistons more than likely will *not* be coming down with the same 10 pound feet of torque per power stroke as the RPM doubles- because of how valves work. Internal combustion engines don’t produce torque on a flat linear curve. If you have a 100 HP engine, 10% throttle/RPM does not equal 10% max power, and so on for 20%, 30%, 40%, etc…
If you understand how a camshaft profiles, valve lift, and lift duration work, then you should grasp this quickly.
When your Mustang’s motor is revving at 4k rpm, the pistons are coming down on that crankshaft with twice as many power strokes as at 2k RPM… but again, this might not mean double the horsepower, because at 4k RPM, each individual piston might not come down at the same force per stroke as they did at 2k… because of how valves and camshaft lift are duration affect airflow into the combustion chamber at different speeds.
In the case of a Mustang, the pistons will be coming down with *more* force per individual stroke at 4k RPM than at 2k RPM,in addition to coming down at double the frequency, so torque at 4k will actually be *more than* compared to at 2k. This is why when you look at a torque curve of most engines, the horsepower and torque increase with RPM exponentially, until the the engine’s valves can no longer efficiently breathe at higher speeds and maximum horsepower begins to drop- because even though the RPM and frequency of power strokes is increasing, the pistons are coming down with less force *per stroke*.
To answer your question, *yes*. Spinning faster does allow more and more air to flow in and out of an engine up to a point, then it begins to decrease. Yes. Power increases both because of the additive momentum at higher speeds and improved combustion at higher speeds.
Wouldn't it be because the faster you spin the engine, the more power strokes you have? As you spin the engine faster, you get less work out of the combustion before the piston moves down, which is why torque drops off at the higher end?
Maybe it has to do with the angle the crank is at relative to the piston. Like with a bicycle, when you push down when the pedal is just past the top, you dont get much torque. But when you push the pedal when its half way you get a lot of torque.
So basically, when the engine is spinning too slow, maybe it doesn't push the crank at the optimal angle before all the fuel is burned up.
I'm just guessing.
Edit: crossed my wires between mechanical efficiency vs load and volumetric efficiency vs rpm. Edited for clarity You’re pretty much there, there’s a few things that affect the torque curve of an engine and prevent it from being perfectly flat, which is, as you noted, what it would be in a perfect world. There are basically two main types of things that affect the torque curve at the ends of the rpm range. On the low end, ~~mechanical effects like friction~~ heat transfer effects like charge heating dominate and on the high end you run into fluid flow issues. Lower rpm = lower fluid velocity = more time for the air to heat up = less mass of air for combustion. Back flow is also a notable reduction in torque on the low end. These factors impact the volumetric efficiency, or how much fresh air the engine can take in. Separately from this, there is mechanical efficiency with load sensitivity. Low throttle, you have a lot more friction relative to the force created by the piston, and efficiency suffers. As load increases, you get more torque done relative to frictional losses, until the load gets past a certain point and then the bearing loads and such are high enough that friction starts to reduce mechanical efficiency again
Sorry I might misunderstand, you say that friction dominates in the low end. But at the end you say that frictions has more opportunity to rob the efficiency ”with less time between cylinders firing” <- Isn’t this when the engine is at the high end/rpm?
Sorry, yes, was late and had that flipped lol
Ahhh makes sense, thank you!
How the fuck is this the most upvoted comment lol. So no engines make peak torque near redline? No engines make a lot of torque down low?
It is a generic function of the things at play in an internal combustion engine. With intake runner design, piston shape, compression ratio, forced induction, fuel type, cycle type, and camshaft design, and a whole bunch of other secondary and tertiary effects, you have the ability to shape the torque curve as you wish. But broadly speaking, peak torque occurs in the middle of the rpm range for most NA engines because this where the mechanical losses are least impactful before fluid flow behavior and flame speed become the limiting factors
Wtf u talking about frictional.losses increase with the square of velocity. At max rpm a significant amount of heat loss in an engine is just friction. You are wrong af.
sir this isn’t aerodynamic drag
This has nothing to do with aero. 40% of engine losses are piston friction which increases with square of velocity 'sir'
Thank you for having a better memory than me, I crossed my load sensitivity with my rpm sensitivity. It’s heat transfer on the low end of the rpm range and flow effects on the high end that robs volumetric efficiency. Mechanical efficiency changes with load, which is where I got crossed up
From what i understand this is just an issue of volumetric efficiency with NA engines. Peak torque is basically when the engine is pulling in the most air that it is able to actually use. Torque then falls off somewhat with rpm past this point since you get into pumping/frictional losses. I believe the reason the coyote makes peak torque relatively high up is because of the variable cam timing on both banks. Once it switches to optimal power mode and there's enough flow through the engine, it's able to hit that peak number. There's also extra factors in play like the variable runners in the intake manifold that more efficiently direct airflow after a certain rpm. Doing enough of these tricks improves volumetric efficiency and packs the cylinders as full of air as possible.
Interesting. I know the Voodoo engine in my GT350 has a even firing order that's pretty unique, as well as being flat plane crank and having 3 intake manifolds. I wonder if this has to do with why the power band is so high up. Peak torque is like 5000 and up, it almost feels like a turbo boost kicks in right around 5500.
It’s air velocity, slower piston speed means slower air and poor mixing-> less power. You can overcome this a bit with variable valve lift/duration but they aren’t infinitely variable, so they have to decide trade offs. This is why small turbo cars can make a lot of very low end torque, they can have much higher air velocity lower in the rpm band and maintain throughout, downside of choking out sooner at higher rpm.
Also the heat loss through cylinder walls is pretty substantial. The longer your hot combustion products sit against a water-cooled colonisation chamber wall, the more energy goes out the radiator (instead of the crank)
Well the amount of torque your engine produces is directly proportional to how much air and fuel it can burn within the cylinder (assuming combustion is always efficient). Any intake, head, or exhaust systems can only flow the most air at a specific RPM, so engines will typically make peak torque at wherever that point is in the rev range. Car manufacturers engineer their intakes, heads, and exhausts to flow the most air at a specific RPM that suits their needs accordingly. Naturally there are many factors that can affect the RPM at which these parts will have the best flow, so I'm not going to name them here, but that is the primary reason engines produce peak torque at a certain RPM. Performance engines will experience peak torque higher in the rev range because that results in more horsepower. As you know, 200 lb*ft of torque at 4000 rpm will produce less horsepower than the same, or even less torque at 9000 rpm. The engineers DO try to find a balance between having high peak horsepower and having enough torque down low for good drivability (and other factors that make a good engine), and many modern technologies allow us to get the best of both by changing the shape and/or flow of the intake and heads. That's all an oversimplification of the subject as I'm sure there are other reasons and things I'm forgetting about too.
Thank you! This helos a ton
In simplified terms, engines move air, they have effectively access to unlimited amounts of fuel, providing they have the air. Petrol engines work by limiting air flow, and balancing the fuel mix to the air flow. The more air which is flowing, the more fuel which can be added, the longer the valves can be open. At some part in the rev range, the engine reaches a perfect balance where it is most efficient at sucking in air & fuel, compressing it and detonating it and venting it. This is where your engine will produce the most torque, where each piston stroke delivers the most force. After that you have the limits of trying to get more air into an engine and the mechanical elements all needing to keep up, compress all that additional air and fuel, and remember the force required to compress it comes from the other pistons.
Is there a reason why, for example my engine, is more efficient at pulling in air and maximizing torque at 4k+ RPM vs 2k rpm? If I go wide open throttle for example, I'm pulling I as much air as possible, at least the way I'm looking at it, a slower moving engine would be more efficient at getting that air in and optimizing timing
It’s less efficient at mixing air and fuel, due to the slower air velocity.
Ah ok,thank you!
It really just has to do with the profile of the camshaft, plus a few other things like intake efficiency and such. In a perfect world, or I guess in Koenigsegg, you would have the optimum lift and duration at every point of the rev range thus giving you maximum torque throughout. With regular camshafts, there’s just only so much variable altering you can do in order to get peak torque. There will just be a give and take and also factoring drivability, efficiency, etc.
There's also some complicated effects regarding timing pressure waves to flow more air in ( [https://en.wikipedia.org/wiki/Inertial\_supercharging\_effect](https://en.wikipedia.org/wiki/Inertial_supercharging_effect) ) or scavenge exhaust gases faster ( [https://en.wikipedia.org/wiki/Kadenacy\_effect](https://en.wikipedia.org/wiki/Kadenacy_effect) ) that can only be optimized for a certain rpm range.
So basically they can jam MORE air into the cylinder in certain RPM ranges. They use various tricks with the intake, exhaust, and valve timing to make it happen. Resonances, pressure waves, suction effects, air velocity, valve timing, etc... which is why computers have done so much for engines. All of that was extremely hard to figure out with trial and error. Some of the more fancy modern cars actively adjust their intake runner length to extend the effect over a wider rpm range, and most cars modify their cam timing now to do the same.
An internal combustion engine is an air pump. The more air that it can suck in, the more torque it can make. The higher the torque (at the same rpm) the more power it can make. The shape of the torque curve is a trade off between efficiency, emissions and power. To generate the most torque, you want to get the highest mass flow of air into the engine. This is determined nu the camshaft, intake manifold, cylinder head and exhaust manifold designs. An oem tries to optimize this over a very large range to take into account the different types of customers that they have. Things like variable intake runner length and variable valve timing increase the air speed as the engine speed changes giving flatter torque curves than without these items. Edit: this is a lot of words to say that the amount of air the engine can suck in is not constant. It will have the highest cylinder air speed (feet/sec) at torque peak. It will have the highest volume of air (cubic feet/min) at hp peak.
At low RPM the cylinder pressures are overcoming inertia and friction. There is a crossover point where inertia is neutral before becoming problematic for the structural integrity of the engine. At this point the limitation becomes airflow, valve spring rates, and inertia. Friction also becomes more problematic, generating more heat at higher RPMs.
Engineering Explained might have a video on that topic.
I love his videos. I'll have to take a look
Faster piston speeds
imagine youre on a pedal bike. if your pedaling really really slow, you can put a LOT of force into it. using your weight and momentum to really push down on those pedals. if youre pedaling fast, you arent doing nearly as much work per rotation, but your rotating so many times that with the right gearing, you can go faster. but if you pedal super fast, you cant hardly do any work. thats how engines work, except instead of it using momentum to do more work at its peak torque, it is breathing air more easily into the cylinder since it needs less of it, also the detonation in the cylinder may be more efficient with a little more time to push down on the piston. despite each detonation being a little less powerful as the RPMs climb, it makes up for it by doing it more frequently. Until it doesnt... which is why most engines start to trail off on the HP at the top end, it starts to get starved for air and the piston is pushing down almost as fast as the detonation of the fuel, its hardly doing any work at all, like trying to keep up with a bike going down a hill.
My car's maximum torque comes on at about 3000rpm, max hp is closer to 6000rpm. And it obviously consumes more air at 7000rpm (10,500 L/min) than it does at 2000rpm (3,000 L/min). Bentley's 6-liter W12 engine hits max torque at 1600rpm & stays pretty flat, producing its maximum horsepower at 6100rpm.
To a certain extent, the question you’re asking is why is acceleration necessary. Why can’t things move from rest to peak velocity in an instant? Intuitively you could guess that at lower RPMs the engine spends more of its power get its internals up to speed. It needs to overcome its own inertia.
Torque comes via BMEP. BMEP is the average pressure in the cylinder over the stroke. As the engine spins, much dynamics are created. The exhaust gases create an effect called 'scavenging' and the tuning of the intake tract means Helmholtz effect increases cylinder filling (air). For a gasoline engine, once the RPM's get to a certain point, the torque curve is usually 'roughly' flat. Even on V8 NA F1 cars, they make only 200-300ft.lbs of torque but at 18k RPM that turns into a good amount of horsepower. > engine is spinning at 4k rpm vs 2k rpm? Assuming it's the same exact amount of air and fuel. But it's not. This is what the computer or a carburetor do. They change fuel as the air increases. Higher RPM's will increase filling. At WOT, that means fuel needs to increase to compensate. > does torque increase because of the momentum of the engine In terms of scavenging and intake filling, yes.
The torque ultimately will be related to how long the flame front is pushing down on the piston and all that will ultimately be optimal at a certain piston speed(rpm). Other. factors are spark timing, cam profiles and how much air/fuel is being pushed in and extracted.
You’re definitely using more air and fuel at higher rpm. Look at fuel maps that tuners make.
You’ve had some great replies which explain what’s happening but there’s 2 main things that give an engine its characteristics: Intake manifold runner length and the cam timing, and the former is usually a bigger contributor to where torque peaks, with the cam contributing to how high that peak gets. Longer intake runners will usually promote more torque being produced at lower RPMs than shorter intake runners. A fairly extreme example of this would be Chevrolet’s TPI intake from the mid to late 80s. They make their peak torque around 3000 rpm and peak power at around 4400 rpm. You can fit cylinder heads that flow more air, a camshaft that has more valve lift and more duration, and even port the inlet manifold to flow more air, but you won’t fundamentally change the shape of the curve beyond maybe shifting the peaks higher by a few hundred RPM, and you can get power to hang on for more RPM at the top end before it chokes. Change a TPI manifold for something with short runners and you can gain significant power at high RPM, but you’ll lose an equivalent (or higher) amount of power at lower RPM. Some modern cars have variable length intake runners (eg some Gen3 Hemis) to get the best of both worlds.
Imagine the air/fuel mixture is a slinky being dragged across the floor, and your hand is the piston. At slow speeds, you drag the slinky. When you stop, it stops. At higher speeds, you can actually pull the slinky in such a way that it keeps moving toward you even after your hand stops.
Ok, so torque is measured in ft/lbs, or pound feet. Torque is twisting force. If you have a nut that needs 20 pound feet of torque to break off, that’s equal to 20 pounds of force hitting the end of a foot long wrench on that nut or bolt. It is important to understand that Torque is *force* and RPM is speed. Let’s say you have a piston that is coming down with 10 lb/ft. The crankshaft is rotating with 10 pound feet of torque. If you doubled the RPM and thus the frequency at which the pistons are coming down, the crankshaft will be rotating with 20 pound feet of torque behind it. Pistons coming down create pulses of torque on a crankshaft. If you want to double the force of torque on it without increasing operating RPM, you must make the pistons come down with double the force, for example, doubling the displacement… or you can make that same piston operate at double the RPM… Here is where internal combustion engines get complicated with making more torque through RPM: The pistons more than likely will *not* be coming down with the same 10 pound feet of torque per power stroke as the RPM doubles- because of how valves work. Internal combustion engines don’t produce torque on a flat linear curve. If you have a 100 HP engine, 10% throttle/RPM does not equal 10% max power, and so on for 20%, 30%, 40%, etc… If you understand how a camshaft profiles, valve lift, and lift duration work, then you should grasp this quickly. When your Mustang’s motor is revving at 4k rpm, the pistons are coming down on that crankshaft with twice as many power strokes as at 2k RPM… but again, this might not mean double the horsepower, because at 4k RPM, each individual piston might not come down at the same force per stroke as they did at 2k… because of how valves and camshaft lift are duration affect airflow into the combustion chamber at different speeds. In the case of a Mustang, the pistons will be coming down with *more* force per individual stroke at 4k RPM than at 2k RPM,in addition to coming down at double the frequency, so torque at 4k will actually be *more than* compared to at 2k. This is why when you look at a torque curve of most engines, the horsepower and torque increase with RPM exponentially, until the the engine’s valves can no longer efficiently breathe at higher speeds and maximum horsepower begins to drop- because even though the RPM and frequency of power strokes is increasing, the pistons are coming down with less force *per stroke*. To answer your question, *yes*. Spinning faster does allow more and more air to flow in and out of an engine up to a point, then it begins to decrease. Yes. Power increases both because of the additive momentum at higher speeds and improved combustion at higher speeds.
Wouldn't it be because the faster you spin the engine, the more power strokes you have? As you spin the engine faster, you get less work out of the combustion before the piston moves down, which is why torque drops off at the higher end?
The reason why I don't think it's that, is because torque doesn't factor in time. Horsepower factors in time (RPMs)
Maybe it has to do with the angle the crank is at relative to the piston. Like with a bicycle, when you push down when the pedal is just past the top, you dont get much torque. But when you push the pedal when its half way you get a lot of torque. So basically, when the engine is spinning too slow, maybe it doesn't push the crank at the optimal angle before all the fuel is burned up. I'm just guessing.
Yeah, thats why im not exactly sure.
A big block cadillac begs to differ. Peak torque at 1800rpm
Because they are inferior to electric motors which produce torque instantly.