WHY are HORSEPOWER and TORQUE CURVED?
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- เผยแพร่เมื่อ 29 เม.ย. 2024
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Let's say you're idling at 600 rpm. You put the car in gear and you floor it, you open the throttle completely. It takes a fraction of a second for the butterfly valve in your throttle body to open fully and allow large amounts of air into the engine. The air takes even less time to actually get into the engine and it takes the injectors another absolute miniscule amount of time to deliver the fuel needed to match this air.
So everything the engine needs to be build maximum power and torque is delieved in a split second. Maximum air is allowed into the engine and we can deliver maximum fuel pretty much instantly. So why doesn't the engine deliver maximum power and torque instantly? Why does it need to rev higher to make maximum power? Why can't it deliver that same power right after idle if we're giving it everything it needs to do so? Why can't internal combustion engines generate instant torque like electric vehicles such as a tesla can?
Why is power and torque a curve and not just a flat line?
Well the answer is piston speed! Why piston speed? Because the speed of the piston determines how much air can actually get into the engine. A fully open throttle body may ALLOW a lot of air to potentially get into the combustion chamber. But how much of that air actually gets in is determined by the piston.
But aren't intake valves what determines how much air gets into the chamber. Zero air gets into the chamber when the intake valve is closed. the timing of the intake valve opening and the duration of how long the intake valve stays open actually determines how much air gets into the chamber. Well yes, technically this is correct. But the valves too are just like the throttle body. A fully open intake valve creates potential for maximum air to enter into the engine, but whether maximum air actually gets into the chamber is determined by the piston. How does the piston do this?
Well it's actually pretty simple. When the piston moves down the bore it creates a void, or vacuum, an senescence of air. When this absence appears air of course moves to fill it. This vacuum which is constantly being created by the piston is the true source of the engine's appettite for air.
Now the higher the engine rpm the faster the crankshaft spins and the faster the piston travels. Now the faster the piston moves down the bore the faster it creates more vacuum and the faster the air rushes into the engine. And this is why power and torque are curves. At 700 rpm the piston simply doesn't travel fast enough to create enough vaccum to ingest maximum air.
But when the engine builds up 5000 rpm the piston travels fast enough to ingest the maximum possible air and then you match that with fuel and you get the maximum possible combustion intensity which generates the maximum possible combustion pressure which pushes the piston down with maximum force then using the connecting rod and crankshaft pin as leverage the piston causes the crankshaft to rotate at maximum torque.
But forced induction engines don't care about the vacuum generated by the piston because they can use a turbo or supercharger to stuff in more air than a silly little vaccum could ever hope to create? True, forced induction increases power but again no amount of forced induction can create a flat power and torque curve. A turbo needs a sufficient amount of exhaust energy to be driven at sufficient speed to generate maximum boost, and the engine can only generate this maximum exhaust energy at certain rpm. Same goes for the supercharger which is driven by the crankshaft usually via a belt so it's rotation speed is actually synced to the rpm of the engine. And to achieve maximum boost the supercharger also needs to achieve a certain rpm. And although some very modern turbocharged engines can generate maximum torque starting from as little as 1500rpm and keep it flat for most of the rpm range thanks to modern ultra low resistance and ultra smart aerodynamics turbos and continuously variable valve timing and valve lift.....maximum power is still always generated at a much higher rpm.
So here's the next level question for you: How can maximum torque be generated at much lower rpm than horsepower. Aren't the two linked together because horsepower is essentially torque x rpm. So why doesn't the horsepower curve simply follow the torque curve? Why don't they look the same?
The reason behind this is that horsepower is essentially torque x rpm.
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#d4a #horsepower #torque
00:00 Why are they not flat
02:29 Gates and piston speed
05:10 Forced induction and vacuum
06:41 Why peak torque before peak power
09:04 Why do they fall off - ยานยนต์และพาหนะ
Another thing to take into consideration is thermal efficiency - the faster the piston speed the less time the heat generated from the fuel has to leave through the cylinder walls.
Simply put, the laws of physics don't produce straight lines; they don't even produce even curves, evidenced as orbital math by planetary/celestial orbits, which are elliptical.
Also combustion process speed, volumetric efficiency, combustion chamber pressure, swirl and quench, fuel atomization etc...
@@jeremiaswitt1374 combustion speed and cylinder pressure are directly related, as are swirl, atomization and volumetric efficiency (VE was mentioned in the video). But yes, there are all these factors which shows us that it's not always as simple as putting A and B together.
I would love to understand engine efficiency, particularly as compared between engine types like diesels and two-strokes.
@@colvinwellborn you would need a computer to sinulate those scenarios because if you try do math with moving parts it'll take a LOT of time. But overall, 2 stroke diesels get very good efficiency, partly because the resistance:torque ratio is different from 4 stroke diesels. But of course breathing is a little inefficient in comparison.
another great video, im always suprised by how i will think i know a solid 80% of what there is to know about a topic, then I watch your video and become humbled
I feel exactly the same way! I'm like, I know this... then watch the video and my jaw drops at how little I know.
Couldn't of said it better. I always go from "yea I know" to "o damn I didn't know that"
My dad always sayed: the more you know the more you know how little you know.
Dunning-Krüger effect. It doesn’t mean we’re dumb, though. It just means we’ve got a lot to learn
The main reason for the reduction in BMEP (and thus torque) at low speeds is the heat lost to the cylinder (due to the long time between ignition and BDC), and the tradeoff between combustion chamber geometry during the timing of the combustion event (delaying combustion so the high pressure coincides with a favorable rod-crank angle will decrease the effective compression ratio).
Other factors include reduced inlet air velocity for mixing and complete combustion, more time for leakage per engine cycle, and being outside the range of speeds the intake and exhaust have their resonances tuned for.
The "pistons not moving fast enough to suck air in" fails the sniff test. The pistons moving slowly gives more time for the cylinder to fill. At very low speeds, the cylinder pressure will be equal to the manifold pressure at the end of the intake stroke.
I think he's plain wrong, sadly. Usually I'm plain wrong, happily
Let’s not forget pumping losses when the throttle is closed.
Oh thank God, I thought I was being stupid to worry about his comments on piston speed and vacuum. PV still = nRT whether the piston moves quickly or slowly. Your explanation makes complete sense, but I wasn't figuring it out on my own. Thank you!
I concur with your last paragraph. Thanks.
This is what i was thinking watching the video. It was not mentioned how the cam profile shifts the powerband either aka efficiency at a given rpm.(just to mention one thing, this video is about why it's a curve)
Of course in conjunction with the diameter of the ports, intake and exhaust. There is much more factors in what determine the powerband in an engine. Piston speed does matter, and in conjunction with the venturi effect, can have cylinder air volume bening in the positive even when no forced induction is present.(which also affect the curve)
The torque curve is almost entirely down to how much air gets into the engine per cycle, it's got very little to do with how many cycles happen per second. How much air gets in is a result of tuning. If you close the intake valves at bdc you get almost 100% of the air into the engine at low revs, but less in at high revs. If you close them later you get better higher end torque because of the momentum of the intake charge (and wavefront if your port is properly tuned) forces more air in even when the piston is coming back up.
That's why a lot of modern engines have such flat torque curves: variable valve timing.
As others have said, at low revs you're limited by the amount of heat rejected into the cylinder walls, while at higher revs you're limited by the breathing capability of the intake and exhaust. (edit: exactly as you said in the latter part of the video)
Upvoted. Nicely explained.
@@th3b0yg Thanks. There are a lot of other factors (exhaust valve and port tuning to maximise scavenging for example). I will admit I'm not a mechanical engineer or engine builder, I just know a little bit about engines from interest and tinkering with my cars.
sumarized it precisely
that's why free valve is the pinnacle of combustion engine design (for road cars. not talking about drag racing, F1). almost perfectly flat torque curve from 1500 to 7500rpm. 300hp/l , 43.5 psi bmep. no throttle bodies/pumping loss, independent valve lift/timimg/duration controls how much air goes in, how many valves are used, and how hard the turbo is spooled up, acting both as anti lag, waste gate, you can theoretically do cylinder deactivation(not very likely to happen on a 3cyl though?) , skip revolutions at low loads, you can also do air brakes like on semis.
you can do different cycles to like Atkinson, or heck you could even run a 2 strokes cycle, although probably not very efficiently, considering its not designed for scavenging like a 2 stroke cylinder with ports, and has no expansion pipe. also who would do that to a 2M car 🤣🤣
@@geemy9675 the problem right now is that freevalve has not been shown to run for any decent amount of time, and not on any production engine. If you haven't already you should look at Fiat's Multiair. It can achieve many of the same benefits of freevalve with the added benefit of being out in the wild for many years as a proven product.
There are many other variables, though I think he touched upon the primary ones. Parasitic losses from bearings, thermal efficiencies, variable valves, etc all factor in. The biggest factor that comes to mind for me, especially for why torque drops off in higher rpm, even if the valves and intake are not a restriction, is the flame front and the time it takes for the pressure to build after ignition. At higher rpm the fuel air mix has less time to burn, thus providing less pressure, thus less torque. At extremely high piston speeds the piston may even outpace the flame front, at which point the engine rpm is usually self-limiting. This situation is not normally possible on most engines due to other factors and is obviously avoided by engineering design (piston speeds in this range also risk con rod or wrist pin failure, or simply overheating)
I also think so. Hhighly dynamic processes are at work here (mixing of gases, combustion, flame front speed, pressure build up), and they simply behave differently depending the period of time (=rpm).
I even think the explanations of that dude are wrong. He basically says that a slow rpm engine (so slower moving pistons) burns less air then a high reving one and so the combustion of less air (+less fuel) generates less pressure (=force on the rod)... but that does not apply here imo. But that just explained the increase of horsepower, not the of torque. We have to think about a single stroke here. Under ideal conditions, you always get the displacement fully filled with air regardless of the rpm.
Another way to think about this is to break it down into two different ideas: an engine spends half its time basically pumping air, and the other half extracting power from the air. Engines work best when the intake air is turbulent and mixed well, and at low RPM the only way to generate that turbulence is by sacrificing airflow, but sometimes that isn’t possible (DOHC).
I don't understand the problem/question yet but I'm looking forward to the answer already.
Dude same! The answer makes more sense then the question. But the question doesnt make sense. Which means nothing of this makes sense too me!😂🤨
Maximum torque is when cylinder fill is best, i.e. highest cylinder pressure when the intake valve closes. Higher rpm tends to decrease this, as flow resistance from the intake tract becomes higher. Due to some nonlinear effects, torque isn't maximized at minimum rpm. Piston speed, however, is not the chief reason for this.
At 4:17, the video notes that at 700 rpm, there is not enough piston speed to pull a lot of air into the engine. This is true, that is why power is low. But it is not the reason that torque is low. Torque is not about how much air the engine can suck in per unit time, but about how much air it can suck in per crankshaft rotation. At higher rpm, pumping losses from the intake tract increase, but nonlinear effects such as scavenging can still cause an optimum, leading to a peak in the torque curve.
Back in the 60s, a company called Turbonique sold superchargers that were independently powered by a gas turbine with its own fuel supply (of literal rocket fuel!). Since they operated completely independently of the engine itself, they could provide full boost at any RPM and had no parasitic drag.
That’s amazing
Thank you very much for making the description very complete and detailed, as I don't understand English, I can translate and understand the video and its animations clearly.
Positive displacement superchargers generate flow. The engine's momentary valve opening restricts this flow, causing a rise of pressure. This pressure rise is nearly constant until dynamics of intake valve opening and mass-spring relationship of the intake charge limit flow.
Unfortunately, most positive displacement superchargers have leakage at apex seals and this is why idle speed boost is limited. Most positive displacement superchargers have boost bypass for all but wide open throttle position
Hey, i have been a long time fan since your original mr2 videos! I hope you can take the time to learn from me a little that i have from you!
I'm sorry to say that this might be the first video that i saw of yours that I disagree with. And allow me to explain: I believe it to be more of a fluid dynamics problem: air being our fluid. In a low RPM (quasi static) scenario we would only accept as much air as the piston displaces (for a given air density as a function of temperature, pressure, humidity, oxygen concentration, etc...) And in this scenario, the air in the intake system itself is stagnet and not flowing. A fairly easy calculation.
However; when you get the intake air moving, there is mass moving in this fluid that is able to supply a larger amount of air (oxygen) in the piston than the piston displacement would allow for. Effectively increasing the compression ratio. This continues as rpm increases, airflow increases more air is allowed in until the rpm reaches a point where you get diminishing returns: the piston reaches the end of it's lower stroke before the air can fully fill the cylinder. This is bad for HP as you are no longer burning as much as you were prior.
The larger intake tubes and air passage ways come again to the idea of air flow: smaller channels experience boundary layers in fluid flow and make it much harder - imagine blowing a breath through a small straw versus a larger boba straw: not only is it easier, but it is faster as well.
As for the fluid flow having the real energy in increasing HP, look no further than water hammering in hoses: it is much harder to stop a fluid while it is moving that stationary under pressure. But that is much more devastating in water because it is an incompressible fluid. Our case air, we do not see that drastic spike in pressure, but a mor mellow hump, this spike of pressure from our air moving and then being stopped by the piston effectively increases the pressure, thus the oxygen content for combustion.
One affect that is conveniently tied to rpm is the time that the pressure chamber has to leak. I'm sure you have tried cranking and engine over by hand slowly with the spark plugs still in and you can feel the compressing strokes and hears a hissing sound. This hissing sound is pressure escaping through piston rings and hopefully not valves or gaskets! All that hissing is power losses as blow by. So the faster that you can go through a cycle the less time there is for this loss to occur. I'm also sure that as rpm increases so does temperature of the piston and piston rings: thus expanding and making smaller gaps for the rings to have blowby.
Also as a final statement of your interpretation of power being tied to rpm, think of the limits. No power at 0 rpm and no power at infinite rpm since no air can enter the chamber at these speeds.
I honestly read the whole thing, twice. So basically the reason for torque being a curve is blow-by? Or did I misunderstand?
@@d4a Yeah i was a bit all over the place on that one. Currently running on fumes as it is my finals week!
To summarize air flow can be seen as a mass moved per unit time. The cylinder in a single intake stroke has limited time to allow this air flow to occur. Slowly moving air towards the cylinder, say from the displaced air from the previous cycle or nearby cylinders, will have an easier time flowing into that cylinder than the stationary (static) air i was talking about.
I suppose this might be a better analogy: say you have half a second to fill up a balloon through a 25 ft straw. You can't start blowing until a bell rings. You have 1/2 of a second to fill it up. You would barely notice this filling up as it would take time to compress the air in the balloon and in the straw, but also the pressure wave sent down would delay your filling times.
Now imagine you were already blowing through the straw and air was coming out the other end. When the bell rings the balloon would be placed on the straw filled for the half second then removed.
This is similar to the automotive topic,but with a positive pressure wave instead of a negative one through the straw/intake
It is this difference in air put into the balloon that related to the cylinders being filled with more air. But at a much more drastic degree since at 5000 RPM i get 6 thousandths of a second for the air to flow in (5000rev/min *1min/60sec)^-1 =0.012 second per revolution. Intake is half a rev so 0.006 second for air to squeeze into the cylinder passed the valves.
If it's still unclear maybe i can hop on a zoom/discord call and work my MS paint magic and show some pressure diagrams.
Cheers!
@Heath M I understand what youre saying, and the balloon analogy is great, however it doesn't take into account the valves. When an intake stroke is completed the valves seal and prevent airflow. this means that the air simply wont go into the port for that cylinder, the air already sitting in the port has become stagnant and therefore any benefits seen from the inertial force of the air mass is negated. i would imagine that this is especially true in the case of uncovered ITBs, meanwhile in a more conventional intake manifold you may see a slight benefit from this however i cant imagine it would be much.
If the effect you described were taking place, and even if it is, if the effect was big enoigh, then we would see more power at lower rpms after an upshift since the air velocity would be high when you are in the lower gear at high rpms, then after a quick shift you would lose some air velocity but it would still be higher than without the downshift (assuming the shift was done quick enough).
You say that the reason that it starts to decrease is due to the piston reaching the end of the intake stroke before theres time for the air to fill the cylinder however this contradicts your own logic, air velocity would be faster at higher rpms and so it would be able to fill the cylinder faster as well and before it reaches the end of the stroke. the true limitation for power simply comes down to what he said in the video about air restrictions from valve size and throttle body size.
Also you mention breathing through a small straw vs a boba straw and say that with the boba straw it would not only be easier but faster, you seem like a smart guy surely you know that the air velocity would be higher in the small straw since you dont have as large of a cross section of air and so the only way to get the same amount of air mass through is by having it be faster. the boba straw meanwhile can easily allow a large amount of air mass through without needing fast velocity to achieve it. Unless you mean you would be able to get the whole breath out faster, in that case that relates back to how throttle body and intake valve size relates to diminishing power at high rpms.
Im sure I missed something but i cant remember the whole argument, either way what you're saying makes sense I just dont think it causes as big of fluctuations in power as you expect
Great video as usual. a possible suggestion for a future video(s) is hybrid vehicles and different hybrid drivetrains (series, parallel, and power-split/series-parallel) since there's some really cool engineering that goes into hybrids.
@ 4:12 , I heard the "nails on the chalk board" words that paint the picture of air being "pulled" into the engine.. This is IMPOSSIBLE ‼️ Air is a gas. Gases, and liquids, can not be pulled !!
Every time the piston in a naturally aspirated, reciprocating, internal combustion engine travels through its 'intake stroke' , air, and possibly fuel, are PUSHED in to the vacated space by ATMOSPHERIC PRESSURE ‼️
Even at higher piston speeds, where a 'ram effect' takes place, the air is being pushed from the higher pressure areas to the lower pressure areas during each and every intake stroke ‼️
I am fascinated by the range of subjects you cover !! Keep it up !! 😉 🙋🏻♂️
Respectfully I would like to raise the question of combustion speed in relation to the powerband at higher RPM... EG it takes an amount of time to combust the fuel/air mixture and as you increase RPM you need to advance the timing (Eg setting off the mixture earlier and earlier in relation to piston TDC giving enough time for peak cylinder pressure to occur shortly after TDC resulting in more power). When you have larger displacement cylinders if the piston is moving at really high speed/rpm the combustion literally doesn't have time to fully occur as the flame front isn't instantons resulting in less peak pressure on the piston/less power output as RPM increases. Hence smaller displacement cylinders (or rather, shorter crank distances) allow for much higher RPM as the physical distance for the combustion to occur is shorter allowing for higher and higher RPM.
The old F1 V8 engines had really short stroke lengths to allow for higher and higher RPM and conversely when you "stroke" a V8 engine with longer stroke the RPM limit tends to be lowered (although you make more torque/power overall due to increased displacement). This is why "Stroker" V8s are great to drive on the road (Lots of power down low) but aren't suited for racing.
Also the other thing I thought was worth mentioning is the "Flat" torque curves you see in modern engines are solely a result of tuning and NOT the natural torque curve of the engine. This is because gearbox/driveline components are rated on their torque limit (Remember torque breaks things, NOT horsepower), so engine manufactures tune their engines to not exceed this limit but stay as close to it for as long as possible (thus giving maximum effective horsepower over a wider RPM range without breaking parts).
Anyway as always loving the video (And hope my comment came across as constructive and not argumentative).
Cheers
I really love the insight that comes from this channel - from the very knowledgable comments as well as the great explanations in the video
For a long time I've know that long stroke means less available RPM because piston acceleration is increasing as length of stroke increases, so stress on reciprocating parts is also increasing. However, for me it's a pretty new thing to take into account the time it takes for combustion to propagate to the extents of the chamber. So if you trade piston diameter for stroke length (keeping displacement constant, say) you're facing a two-sided tradeoff where RPM gets limited in BOTH directions by different factors. Fascinating!
It seems pretty natural for torque to reach peak and stay flat, though. You will have peak torque when you have a cylinder fully filled with as much air and fuel as the intake (forced or natural) will allow. This doesn't take long to reach, and once it is reached you will flatline it.
It will then stay flat until your rpms speed up so much that you can't properly fill the cylinder and/or pushing the crank through a full rotation can no longer be done efficiently within the given time between explosions--then it will start to drop.
HP will keep rising as torque rises, and then keep rising as rpm rises while the torque stays flat and/or as long as the reduction in torque is outweighed by the increase in RPM. Finally, when torque starts significantly dropping, hp falls.
One doesn't need to 'tune' to create a flat torque line--that's a fairly natural feature of ICE engines.
Excellent video and explanation that I was looking for. thx a lot for it.
Thank you very much for such a clear video.
Thanks, this was very helpful. I was confused on why the torque and power curves are different when they're related with each other.
Air volume per unit of time!
The difference here is that
during high revs, piston will do many cycles per unit of time,
and during lower rpm piston will do less cycles during same time.
Nice work, great topic and great explanation.
Thanks for this video ! Now I understand why some electric vehicles still do have some sort of gearbox. The power band is very large compared to a ICE but it still has a limit.
And I didn't knew the reason behind the falling off of the torque curve, which in turn causes the power curve to fall. But when you know it is limited by the air intake, it all makes sense !
Adding gearing to an electric motor doesn't increase the power band
@forloop7713 no but it allows peak power to be applied at a different speed
@@m5rtin_agpeak power happens at 0 km/h
@@waldolemmer At zero km/h the power output is zero
@@jimb12312 My bad, I meant peak torque
Excellent presentation as always. Love the channel
For the calculus nerds, power is the integral of torque WRT rpm, or conversely, torque is the derivative of power.
In ship diesels is a way to come around the limitations of high torque at low rpm. When abusing the compressed air from the starting system during run they fill the cylinders instantly. During the next exhaust stroke the turbo wakes up quickly so the compressed air reservoir is not the limitation. The use of nitro oxide will also give instant torque. But if the system starts at idle the engine will throw its rods.
Electric motor torque doesn't fall due to back EMF when the motor is ran with a motor controller. Controller can always step up the voltage to counter the back emf.
Torque is allowed to fall intentionally to prevent overheating of the motor. once the motor reaches peak power it can handle, trying to maintain the maintain the Torque means motor is being overloaded and will overheat.
Always wondered this question thanks for a great explanation,cheers 🇦🇺
It makes alot of sense now. Thanks for the info.
Thanks for the insight, hopefully everything is very different when transmission/gear ratios are taken into account. That might make for a very nice subject!
If I'm not mistaken, the transmission is used to keep the engine in the RPM that have the most torque or power, depending of the engine, the use you have at the moment etc..
Once again very thoroughly explained !
I'm so glad to have found your channel, your an amazing teacher
Another consideration is the exhaust pulse timing and overlap of the valves, David Vizard has attributed more of the low pressure on the chamber being due to the exhaust than the piston.
Its obvious but its easy to forget . I learned some New things, and its good to know when you want to increase the power of the engine. Thank you so mutch for the video and for make an interresting sunday.
Brilliant explanation!
thanks for the explanation, very well done for dummies
Thanks Buddy, so much knowledge in one video ❤️❤️❤️❤️❤️
you're able to clear the doubts that was flying around my head for a long time
Another great video, this channel is awesome! Wish I knew this back in my Gran Turismo playing days :)
Great explanation! Very clear.
Wow! Thank you! I learned a lot from this video!
Great video. Thanks. Greetings from Cuba😊
A very tasteful build, sharp looks, awesome sounds; so envious of the future winner
You forgot to mention one particular type of racing engine. Rally cars need lots of torque at all RPMs.
They need to be able to spin their wheels throughout their RPM range and minimize the number of gear shifts they have to make.
Rally cars tend to have very low gearing too, they aren't aiming for top speed. They are aiming for the best performance in any one particular gear so they can sit on one gear through a lot of technical curves and still get the wheels spinning at a balance point where there's enough slip to go sideways and enough traction to change direction quickly.
Rally cars tend to have a flat torque curve up until around 5500 RPM, where it somewhat sharply drops off. But there's still PLENTY of power left over to hit the rev limiter in top gear for those sprint sections. Top speed tends to hover around 200 to 220 km/h which isn't that slow compared to a road car. But in other forms of high end racing that is slow.
But a F1 car would have a pretty bad day on a rally track, even if it could do 340 km/h which is much faster than any rally car.
brilliant video - thank you for very clearly clarifying the difference between the power and torque curves.
two things I'm not convinced of though!
- at low rpm the vacuum takes longer to build (true!) but there's also more time for it to draw air in. I thought the difference was that the higher air velocity induces more turbulence and hence better mixing of the air and fuel?? (hence why larger valves sacrifice low rpm performance for higher rpm efficiency)
- the dyno charts are usually done at a steady state (balancing engine torque against the dyno resistance), so the lag issue should not matter. Isn't it just that although the inlet pressure is higher with a turbo, the air is only drawn in by the "vacuum" (or pressure difference) in the cylinder: so the explanation is the same as an N/A engine... (but for the turbo, the air will have higher velocity, hence typically a flatter torque curve.)
I don't mean to be critical! I love what you're doing and just want to make sure I haven't misunderstood something!
one more thought ... in turbo engines, the torque often drops slowly at higher rpm before the big drop at peak power. Is this because the turbo can't keep up with the air flow rate required by the engine, causing the inlet boost pressure to slowly drop? (it'd be great to see a chart of boost pressure over-laid on the torque curve)
Thank you ❤
Always great info..
AWESOME sir! At the preview of the video, though I already knew the context in why TQ vs HP have different curves, but I thought it would be interesting to see a Dyno of an electric motor vehicle to see the contrast in power curve vs an IC power curve, and sure enough, bang (spoiler alert @8:00) you did just that!
I really enjoy all of your videos. Very well explained
So clear and precise. ☺
I'd like to see the screw compressor used for the supercharger animation actually be used for a IC engine super charger. That would be one hell of an engine.
Can you do a video on Nissan’s VVEL system in the vq37 vhr. Im fascinated by the flatness of the torque curve on this engine and i cant find a video that explains it in great detail like your videos normally do. But anyway I love your content :)
Thank you for your videos... always cool information 👍 My question is, is it then helpful to airflow/gasflow a cylinder head, if the crank isn't built for higher RPMs?
Good analysis
Mah man with all the sponsors we love to see it. This is all super cool, but I can't wait to see the turbo 4A-GE. ;)
I doubt anyone likes ads 😅 that's why I didn't monetize this video, the squarespace is the only ad
@@d4a Best way to do it IMO. Kind of you. ;)
Piston speed and rpm are directly related to speed of the rotatin crankshaft/flywheel/drivetrain, and it is this rotating assembly that stores the energy we have created, in the form of momentum. A big heavy flywheel takes a lot of energy to get going, but once its spinning at the designed rpm, it takes relatively little energy to keep its momentum going.
Thank you, briliant video!
I never thought of why power is uneven over the RPM range, i kind of just thought for every spark it makes some power and so higher RPM is more pops so the power adds up.
The torque of the engine correlates to volumetric eff. Acceleration of the car at each individual gear is highest at peak torque but not power. The faster engine spins, the faster it compresses the mixture, the faster it compresses the mixture the higher the speed of the flame will be until the power of the engine begins to fade.
Presumably electric turbos can pump more air in from idle RPM.
since they're not directly linked to the exhaust side or the crankshaft, probably. as long as manufacturers don't limit them in some other ways (ex. up to 20% more power draw than what the exhaust side is currently outputting, for power consumption reasons).
electric turbos do not work with building boost , they can blow air but not compress it and are no good at high rpm , standard turbos can run well over 100,000 to 200,000 rpm
@@richardsawtell256 i think he meant the kind of turbo porsche recently patented.
not the fake $100 leafblowers currently on sale.
@@vukpsodorov5446 ohh okay well i have a few JDM subaru twin turbo cars and the primary boosts from idle which i guess that is what they are wanting to achieve
@@richardsawtell256 basically, yeah. but in theory, as an electric turbo isn't connected directly to the exhaust side, it can give full boost at any RPM (assuming a large enough battery is connected to it).
also there's the advantage of the exhaust spinning the turbine even if the compressor isn't running, so it can actually generate additional electricity (quite handy for something like a hybrid).
The answer to all of this is supercharged 2 stroke variable exhaust timing (like Detroit diesel) but gas direct injected. Just need a way to not burn oil & pass emissions
Actually the primary factor in determining the shape of your torque curve is your camshaft profile followed by your intake and exhaust manifolds. Throttle body, int, exh and valve size are all important factors but not primary ones.
The video is not about torque curve shapes. It answers the question why torque is even curved in the first place.
@@d4a
Why the torque curve is is curved fundamentally is due to volumetric efficiency which is determined by several factors - the primary one being the camshaft profile, not the size of the throttle body or valves. Again, those are important but not primary.
Brilliant, as always. It's the only channel where i can find this kind of informations, and easy to undestand. Great job !
because real men love curves
now that's funny
Ha ha ha!!!!!
My understanding has always been that RPMs determine power (and total torque value too to some extent) simply because of the number of explosions for "unit time". At 1000 rpm you have 1000xCilinders amount of explosions pushing you forwards in a minute, while at 6000rpm you have 6 times as many.
The curves normally drop off at the top RPM because at that point the pistons are going so fast that the explosions have little to push off against. The theoretical limit of this is when a piston is going as fast as the expanding explosion, where the explosion is not accelerating the piston any further.
The matter is that volumetric efficiency changes with speed, to make a flute sounding good you can't blow not too strong and not too weak too (it is literally the same phenomenon, in fact, how much you have to blow varies with how many holes (to change the note) you cover, and, in engines there's always to considered the mechanical looses
Nice work ! I see that it is not your core theme, but it would be great if you could do the video about BLDC motors, its curves, efficiency the same way you did here as you explain it clearly.
would also be nice to have an explanation on the efficency curve vs rpm
A positive displacement supercharger has an almost instant boost response, but you still get a curve however it is usually quite flat and rising 😉
I'm very surprised header length, intake runner length, and camshaft timing were excluded from this video, I would say those things are the actual reason why torque curves are shaped the way they are, throttle body, valve size, and piston speed only effects the peak power potential.
This channel is good stuff
You can change the curves a lot with the geometry inside the engine. But it's all linked to air intake and airflow control.
Electric motors suffer from three things: back EMF, switching losses and magnetic limitations.
Back EMF is the voltage produced by the generator capability of a motor fighting the current that wants to spin the motor.
Switching a transistor on or of takes time. The higher the RPM the more switches so we spend more time switching.
Magnetic limitations means as we put more power through a motor it generates heat. Heat and the power weaken the magnet so the percentage of generated heat and noise(electric & magnetic) increases.
In a ICE it's funny a cam system has a constant switching loss over engine rpm as the valves are mechanicaly linked. Also the heat generated inside the engine weakens the materials ability to withstand physical stress and cooling prevents it from failing. Also electric fights back EMF with increasing RPM, ICE fights friction ...
Quite funny how both fight the same kind of engineering problems if you look at the math/physics.
Please make a video about optimal shifting rpm's if you have the graphs and gearbox ratios
This video is great like all of your videos, but why didn't you mention bore vs stroke when talking about adjusting torque and power for specific usage.
Just amazing! I ve been watching your videos and you're pretty much answering all the questions I had in mind for a while without finding a good answer in the internet. So much valuable information that can't be find easily elsewhere
Finally a video on power and torque that I have nothing to add to...
This may be a silly question:
imagine in a particular engine we have the max torque on 5000 rpm . lets open the the carb (the engine is on test stand with no load) until we reach the 5000 and hold it there , so now we have the max torque . This torque comes from combustion force generated at 5000 rpm at the piston top multiplied by the arm length ( length of the connecting rod plus the distance of the crank pin to the center of rotation , which both are constant) . For going to higher rpms ,say 5500, we need to increase the combustion power by opening the carb air intake even more , right? (is there any other way to increase the rpm?) . the question is why in the graph the torque decreases when we have more combustion force ?(torque = combustion force X arm length)
Great explanation, though I feel you should have also mentioned that power can drop off at high revs due to a loss of valvetrain control, or valve float. This is more prevalent on an OHV engine. Also, putting a large TB on a regularly driven car can reduce low RPM perform due to a lack of air velocity, which results is a less complete air fuel mixture and less efficient combustion.
great video as always!
Great Video again. but after watching more and more of your Videos in my opinion a video about gearboxes is missing. because, whats the purpose to know how to perfectly tune your engine if you have a gearbox that wont be able to handle it and there we should answer the questions, how gearboxes are build, what types we have (advantages and disadvantages) and what makes gearboxes strong or maybe how to reinforce them if you cant get an aftermarket box that can handle higher power
combustion speed, volumetric efficiency and most importantly heat generation from the combustion process and friction from ultra-high piston speed. Also even if ultra high piston speeds were to be achieved, another limiting factor would mechanical failure, which could result in joints or solid parts from heat, material fatigue, compression or bending forces in components...etc
What about heat loss to cylinder walls and fuel related topics (combustion speed, mixing and evaporation time) ?
The most simple way to out this is look at the hilix 2.8 engine
It doesnt have a throttle body, it just spins and you add the fuel at the right moment, so really its only going to suck as much as the cylinder bore and stroke will allow it
If you out a turbo on it the engine wakes up alot more because rather than having to work off of the pistom sucking, its got a turbo pushing air in
So clearly explained, keeping simple and synthetic! Outstanding!
Good one!
I disagree with you on several points: 1) A positive displacement mechanically driven supercharger should actually be able to offer higher boost at lower the RPMs, as the effect of intake restrictions (air filter and manifold diameter) are lessened. 2) I have yet to understand why the maximum torque at idle on a non-turbocharged engine is lower than say half the maximum torque at peak torque rpm, I can attribute some of the up to 2:1 decrease to the effects of headers (both intake and exhaust), and the valve timing being optimized for high rpm. Can anyone offer an explanation, please? 3) A variable (hot side) geometry turbo, if so designed should be able to provide boost at idle, more so on diesels.
I'm not very good with forced induction, but I can answer #2 for you.
A few factors for low speed/idle torque.
1. Valve profiles are optimized for peak torque/power, so the valve duration at idle is way too long for those rpms and you end up pushing a lot of trapped charge back out of the cylinder (flow reversion). This is due to the (relative) lack of momentum in the intake/exhaust ports when compared with higher speeds.
Most engines these days have variable valve timing, so idle usually has optimized timing, but there are a few other factors that determine the timing at idle that may keep it out of the optimal torque timing (in cylinder residual, piston to valve clearance).
2. Time - slower piston speeds means more time for the cylinder to soak up the heat in the combusted/combusting gases, which removed energy from the gases and reduces the amount of pressure they can exert on the piston, reducing the torque.
#1 can become a big problem with performance engines that run at very high RPM (>6500 rpm). Making power at those high speeds requires very long duration cams, resulting in terrible torque production at the lower speeds which severely impacts driveability.
I believe with your question 1 about superchargers, you are right that flow restrictions are less, but the increased in supercharger speed and subsequent increase in pressure overcomes the intake system restriction. Peak supercharger efficiency tends to happen near the middle of the rpm range, and I know there are a lot of flow dynamics in the compressor that I cannot speak to that would have a significant effect here as well.
Very timely video. Almost read my mind hehe
The Mercedes-Benz AMG C 43 4Matic has a bi hybrid electric compressor & turbocharger set up capable of achieving a maximum boostpressure of 1.1 bar. With this setup the engine is able to achieve the maximum torque of 520 Nm in the range of 2500rpm to 5000rpm and achieves max power between 5600rpm and 6100rpm of 390.3 PS.
I have designed engines with predetermined designer TQ and HP curves. True, you can't get instantaneous boost from a turbo or supercharger. You can however capture ALL pressurized air in a buffer air tank and not waste air through waste-gate. If turbo is capable of 5-6 bars and engine only needs 1-2 it gets stored for when you want instant and very controllable air flow. Exit valve on air tank adjusts to on demand, or exactly to a predetermined power curve. Valve controls PSI and is different from the throttle.
More RPM = more power because it pulls in more Air/Fuel. Want more power without increasing RPM... increase Boost and it forces more Air/Fuel in without raising RPM. Boost can be controlled independent of engine RPM that controls Turbo or Supercharger.
There is another benefit of over pressuring air in buffer tank. More pressure = more heat. A heat exchanger can remove heat more effectively when the temperature delta is larger. Then just like a refrigerator, when air goes from high pressure to lower pressure, the temperature drops. It's like spray paint, when you press trigger and air comes out, it's cold and the can itself gets cold.
Today with Electronic Forced Induction (Mercedes is using it now), you can always keep a minimum PSI available in the tank regardless of engine RPM. My biggest problem was increasing boost (more Air / Fuel) without increasing RPM. I could make 500 HP at 1,000 RPM if I needed it. Rather than reading Dyno results and publishing Power Curves, I pick the curves in advance and store them in ECU. Push a button and pick mild, medium, or wild power curve. It's 'designer' power.
Thx, but can you do a video about octane boosters, water/methanol injection and ethanol blend fuels for power and to eliminate knock please??
Hey there matey, I would love to see a video on the various electric motors used in EV's today and the tech behind them.
I love how you explain car things. A super video as always!
i thought its because of the cams, because an engine with some kind of VVT system will get you 2 torque peaks on a dyno graph and besides a rotary engine has no peak torque/power peak, it makes more power the higher the RPM
@@TheGiganticNoob I think you are correct.
Good bro
And tell me mileage increase in bike
So which is important tork ya power
The exhaust also effects the amount of air pulled in,
Why doesn't the lengthened cylinder filling time compensate the smaller underpressure (vacuum) during low RPM?
Speak speed got much better. Now I can understand you much better. Thank you
soo soo soo much helpful
My mind always considered the power and torque drop offs were due to inefficiency
i also hear to my profesor says that in high rpms the combustion start to be not perfect because the sark have not the time to iginite all the mix so with high rpms the combustion start to be not perfect.
Great video
Amazing video!
The Ford 300 I6 does make peak Torque off idle. Cam profiles are also an issue.