Horsepower vs. Torque - what really matters

[JMEngineer]

It blows my mind how often I see this argument and how much bad information continues to float around so I decided to put together a factual and educational thread on the topic.


It isn't just kids on forums who have the wrong idea about power vs. torque. I was talking to Kim Lyon a couple years ago at MIS during the Formula SAE competition and he asked me, "Which is more important: power or torque?"
Without hesitation I replied "Power."
"and why do you say that?"
"Because power is power. Torque is just a force that has to be geared out."
He smiled and said, "Exactly. You would be shocked how many teams show up to [Formula SAE] competition year after year and try to tell me that torque is what really matters."

I use that example because even though I know what I'm talking about, I'm still just a guy on a forum to most of you. Kim Lyon has better credentials.
So who is Kim Lyon? He's an automotive engineer. He spent 25 years with Chrysler Powertrain Engineering and has race engineering experience with FIA (LeMans Prototype), NHRA, and F1.
Here is his public LinkedIn profile if you want to read a little more about him: Kim Lyon | LinkedIn


So why do so many people think torque matters? Because it isn't just peak power that matters - it's the SHAPE of the power curve or the average power.
Given two identical cars with the same peak power but one makes more torque, the car with the higher torque will GENERALLY be faster. This is simply because the car with more torque will tend to have a higher average power, but this is not always the case. Below are two examples to illustrate my point. Example 1 is more of a 'typical' example that might give some people the impression that torque really matters. Example 2 is an extreme case where having a boat load of torque doesn't help at all.

Example 1:
Both of these cars make the same 170hp@6000rpm, but Car B will be faster because it will make more power earlier in first gear and won't see as much of a drop in power after each shift. Higher average power = faster.


Example 2:
Both cars have the same peak power and exactly the same shape power curve. Even though Car B makes DOUBLE the torque, both will be capable of EXACTLY the same performance because torque is gearing dependent. If we assume that the ideal 1st gear gearing for Car A is 4:1, then the ideal gearing for Car B would be 2:1. At any given speed, the two cars will be making exactly the same power and will accelerate at exactly the same rate.



Let me explain what I mean when I talk about SHAPE of the power curve before someone gets their panties in a bunch and screams "But you changed the gearing!"

SHAPE of the power curve refers to an x-y plot of power as a function of rpm divided by peak rpm.
Yes, Car B would get off the line quicker if both cars had identical gearing and would win a drag race as long as it didn't run out of gear too fast.
BUT... no matter how fast Car B could get through the quarter mile by optimizing its gear ratios, Car A could match it by doubling that ratio. The peak performance of the two cars is 100% identical because their power curves have the same shape.


If anyone has a legitimate question feel free to ask but please don't try to tell me that torque matters because it really doesn't and there's nothing you can say to change that.


Cliff Notes:
Which one matters?
Power. Period.

[SarcasticOne]

Best example I've seen...

You will accelerate fastest in any gear at maximum torque.
You will accelerate fastest at any speed using gears to give you maximum horsepower.

Sent from my Galaxy Nexus using Tapatalk

[Design]

Originally Posted by SarcasticOne Best example I've seen... You will accelerate fastest in any gear at maximum torque. You will accelerate fastest at any speed using gears to give you maximum horsepower

That's probably the most succinct way to put it. Visually the analogy would look like this:

VW TDI stage 2 (~16.0 @ 90 mph):


MS3 Stock (~14.0 @ 100 mph):

[xfeejayx]

Originally Posted by JMEngineer If anyone has a legitimate question feel free to ask but please don't try to tell me that torque matters because it really doesn't and there's nothing you can say to change that. Cliff Notes: Which one matters? Power. Period.

though I don't completely disagree with you, your cliff notes are an erroneous conclusion, and contradict your first example.

your first example is a clear example of why this is not as simple as "power matters, period". how can you say "the shape of the curve matters" and then say "torque doesn't matter". The shape of the curve is dependent on torque!

also, you've forgotten to take into account different applications. you say 'torque is something that can be geared out', but that's not easy to do on cars that are already built. easy enough to do on a formula SAE car, but not so much on full size cars.

here's an example. say car A makes 300 hp @ 4k rpm (394 ft-lbs of tq), car B OF THE SAME MAKE/MODEL with the same gearing makes 350 hp @ 6k rpm (306 ft-lbs of tq). who's faster? this is basically your example 1 but with one car having more peak HP.

per your "power matters" comment, n00bs will think B would be faster, when in fact it very well might not be since it has more WHEEL TORQUE given the same gearing. of course this can change if B can hold a gear longer, etc etc... again, the "it's the shape of the curve" comment padded this, but the shape of the curve is dependent on torque.

point is, it's not as clear cut as you make it seem. it's not "power.period". The ONLY thing that is clear cut is WHEEL TORQUE. Wheel torque happens to be based on torque, engine speed, and gearing, all three of which are equally important.

but way to get an educational conversation going

[forcedinduktion]

HP=ft*lbs/time

t=lb*ft

[silvapain]

Work is the integral of force over time. If you want to know which engine will be faster (do the most work over a given time), just integrate the force (torque) curve.

In dum-dum language for youz guyz, that means you need to look at the total area under the torque curve.

[Easter Bunny]

Originally Posted by silvapain Work is the integral of force over time. If you want to know which engine will be faster (do the most work over a given time), just integrate the force (torque) curve. In dum-dum language for youz guyz, that means you need to look at the total area under the torque curve.

This is true... the real answer is Calculus.

Gear spacing would also factor into this as well ie. if you make a ton of torque at 2000 rpms it wouldnt matter if your gearing never got you that low in rpms after a shift. For alot of cars you would only be particuarly concerned with the area under the curve from say 4000 - 6000 rpms (range varies greatly based on car and mods.)

[Domino81]

Originally Posted by silvapain Work is the integral of force over time. If you want to know which engine will be faster (do the most work over a given time), just integrate the force (torque) curve. In dum-dum language for youz guyz, that means you need to look at the total area under the torque curve.

Not to strip away any of your credibility but you spelled dumb wrong.

So I look at this as both are important, but a higher TQ number will usually mean more average power therefor result [usually] in a faster car. Correct? If I read and understood that correctly.

[btstarcher]

Discussions like this are what drove me to study ELECTRICAL engineering...

[Domino81]

Will read later...

[captain slow]

http://www.mazdaspeedforum.org/forum/foru...3-990-a-93651/

This thread^^^^ is what started this debate. Read a few pages in and the torque vs hp thing starts.

I say its all about torque because power is a function of torque.

Apparently I'm wrong and "power is all that matters"..... But i'll take the higher tq any day of the week. Torque feels awesome.

[btstarcher]

Originally Posted by freundb http://www.mazdaspeedforum.org/forum/foru...3-990-a-93651/ This thread^^^^ is what started this debate. Read a few pages in and the torque vs hp thing starts. I say its all about torque because power is a function of torque. Apparently I'm wrong and "power is all that matters"..... But i'll take the higher tq any day of the week. Torque feels awesome.

I thought torque was a function of power....WTF....

edit: just checked Wikipedia; fuck....you're right. I always get shit backward.

[silvapain]

Originally Posted by btstarcher I thought torque was a function of power....WTF....

Other way 'round. Hp = Tq * RPM / 5252

That's why the two curves ALWAYS intersect at 5252 RPM.

[btstarcher]

Originally Posted by silvapain Other way 'round. Hp = Tq * RPM / 5252 That's why the two curves ALWAYS intersect at 5252 RPM.

Yep. I remembered the 5252; just got my equation backwards...

[Stealth01]

You also have to define "faster" in clear-cut terms to really argue this. By faster, do you mean 0-60, 1/8 mile, 1/4 mile, 0-120, mile, top speed, etc. From a dig, from a roll?

Take forum wars for example.

500 HP Civic vs 350 HP MS3. MS3 is "faster" because he completed the quarter mile faster, but the Civic was closing fast and trapped higher, if I recall. So which one is truly "faster?"

Technically, every MS3 is faster than every MS6 because their top speed is 155 and ours is 150.

So define "fast" and then start deciding whether HP or TQ is more important, IMHO.

[silvapain]

Originally Posted by Stealth01 You also have to define "faster" in clear-cut terms to really argue this. By faster, do you mean 0-60, 1/8 mile, 1/4 mile, 0-120, mile, top speed, etc. From a dig, from a roll? Take forum wars for example. 500 HP Civic vs 350 HP MS3. MS3 is "faster" because he completed the quarter mile faster, but the Civic was closing fast and trapped higher, if I recall. So which one is truly "faster?" Technically, every MS3 is faster than every MS6 because their top speed is 155 and ours is 150. So define "fast" and then start deciding whether HP or TQ is more important, IMHO.

Both the 155 and 150 top speeds are ECU limited. The GenJuan MS3 is RPM limited to ~180 MPH (6700 RPM in 6th).

[Stealth01]

Originally Posted by silvapain Both the 155 and 150 top speeds are ECU limited. The GenJuan MS3 is RPM limited to ~180 MPH (6700 RPM in 6th).

Understood, but it still shows one definition of "faster."

[captain slow]

Originally Posted by Stealth01 You also have to define "faster" in clear-cut terms to really argue this. By faster, do you mean 0-60, 1/8 mile, 1/4 mile, 0-120, mile, top speed, etc. From a dig, from a roll? Take forum wars for example. 500 HP Civic vs 350 HP MS3. MS3 is "faster" because he completed the quarter mile faster, but the Civic was closing fast and trapped higher, if I recall. So which one is truly "faster?" Technically, every MS3 is faster than every MS6 because their top speed is 155 and ours is 150. So define "fast" and then start deciding whether HP or TQ is more important, IMHO.

This was also apart of the original argument. Fast vs quick. Have the tq to go quick and the higher power will get you to go fast.

@Tokay444 you know you wanna join this discussion

[JMEngineer]

Originally Posted by SarcasticOne You will accelerate fastest at any speed using gears to give you maximum horsepower

^This part is correct

Originally Posted by SarcasticOne You will accelerate fastest in any gear at maximum torque.

^This is only 100% true if you have no resistive force that changes with speed - like wind resistance. But in most cases it's close enough.

Originally Posted by xfeejayx though I don't completely disagree with you, your cliff notes are an erroneous conclusion, and contradict your first example. your first example is a clear example of why this is not as simple as "power matters, period". how can you say "the shape of the curve matters" and then say "torque doesn't matter". The shape of the curve is dependent on torque! also, you've forgotten to take into account different applications. you say 'torque is something that can be geared out', but that's not easy to do on cars that are already built. easy enough to do on a formula SAE car, but not so much on full size cars. here's an example. say car A makes 300 hp @ 4k rpm (394 ft-lbs of tq), car B OF THE SAME MAKE/MODEL with the same gearing makes 350 hp @ 6k rpm (306 ft-lbs of tq). who's faster? this is basically your example 1 but with one car having more peak HP. per your "power matters" comment, n00bs will think B would be faster, when in fact it very well might not be since it has more WHEEL TORQUE given the same gearing. of course this can change if B can hold a gear longer, etc etc... again, the "it's the shape of the curve" comment padded this, but the shape of the curve is dependent on torque. point is, it's not as clear cut as you make it seem. it's not "power.period". The ONLY thing that is clear cut is WHEEL TORQUE. Wheel torque happens to be based on torque, engine speed, and gearing, all three of which are equally important. but way to get an educational conversation going

Which one is faster?.. The one with the higher average power.
The point is that rate of acceleration of a car is a direct function of power. You can go another step back and put the equation in terms of torque, but not without adding the variable of rpm. Torque alone is not enough to calculate how fast a car will accelerate. Power is.

Originally Posted by forcedinduktion HP=ft*lbs/time

If ft*lbs refers to a force and linear distance traveled then you just need a unit conversion factor in there.
Since ft*lbs refers to a torque in this case you also need to add an angle of rotation

Originally Posted by silvapain Work is the integral of force over time. If you want to know which engine will be faster (do the most work over a given time), just integrate the force (torque) curve. In dum-dum language for youz guyz, that means you need to look at the total area under the torque curve.

Work is either the integral of power over time or force over a distance. It's not as simple as area under the curve.

Originally Posted by freundb http://www.mazdaspeedforum.org/forum/foru...3-990-a-93651/ This thread^^^^ is what started this debate. Read a few pages in and the torque vs hp thing starts. I say its all about torque because power is a function of torque. Apparently I'm wrong and "power is all that matters"..... But i'll take the higher tq any day of the week. Torque feels awesome.

When I put all 180 lbs of my weight on a 175mm bicycle crank I'm making 103 lb*ft of torque. Therefore my bicycle must feel faster than my 1000rr which only makes 88 lb*ft.

Originally Posted by Stealth01 You also have to define "faster" in clear-cut terms to really argue this. By faster, do you mean 0-60, 1/8 mile, 1/4 mile, 0-120, mile, top speed, etc. From a dig, from a roll? Take forum wars for example. 500 HP Civic vs 350 HP MS3. MS3 is "faster" because he completed the quarter mile faster, but the Civic was closing fast and trapped higher, if I recall. So which one is truly "faster?" Technically, every MS3 is faster than every MS6 because their top speed is 155 and ours is 150. So define "fast" and then start deciding whether HP or TQ is more important, IMHO.

It doesn't matter how you define faster - it always depends on power before torque.
Traction is another issue.

[xfeejayx]

Originally Posted by JMEngineer Which one is faster?.. The one with the higher average power. The point is that rate of acceleration of a car is a direct function of power. You can go another step back and put the equation in terms of torque, but not without adding the variable of rpm. Torque alone is not enough to calculate how fast a car will accelerate. Power is.

you really need to watch what you're saying, you're mixing correct and incorrect statements, and it's going to lead to a lot of confusion.

agreed highest AVERAGE power wins, but that doesn't mean power=god. The example I gave explicitly said WITH EQUAL GEARING. Once you consider the gearing equal, the car with higher torque has higher acceleration, it becomes strictly a matter of torque.

Jeebus, I just read your reply to @silvapain. not sure it's worth it to continue arguing with you.

n00bs beware, though he's put up some good info, don't take everything he's saying to be fact. the only fact you need to know is that wheel torque is all that matters, whether that comes from torque, gearing, or engine speed, or a combination of those three. whoever has more wheel torque accelerates faster (of course weight of the car and such play in also).

[Crarrs]

Originally Posted by JMEngineer When I put all 180 lbs of my weight on a 175mm bicycle crank I'm making 103 lb*ft of torque. Therefore my bicycle must feel faster than my 1000rr which only makes 88 lb*ft.

The real point of that should be that you're only making that peak 103 lb*ft at 0 RPM on the bicycle. Sure, that's a lot of torque, but once the bicycle starts moving and the angle of your crank moves, you're no longer applying that force to the full 175mm lever arm. BUt the CBR is making that lower torque at 10,000 RPM, all day, every day, and that's where the power component matters. Work over time. lb*ft/s^2

[JMEngineer]

In the case of equal gearing then yes it is true that the car with the higher instantaneous torque will accelerate faster. But since both are at the same rpm, whichever car is making more torque is also making more power. If you want to calculate what that acceleration should be you can either use power or torque times rpm... which equals power.

What exactly have I said that isn't fact?

[xfeejayx]

Originally Posted by JMEngineer In the case of equal gearing then yes it is true that the car with the higher instantaneous torque will accelerate faster. But since both are at the same rpm, whichever car is making more torque is also making more power. If you want to calculate what that acceleration should be you can either use power or torque times rpm... which equals power. What exactly have I said that isn't fact?

nobody said anything about same rpm.

"what matters? power. period" <<---not fact

i understand what you're TRYING to say, and I agree with what you're thinking, but what you are typing is misleading. power at the motor (assuming gearing is variable), torque at the wheels, that's what's important.


and btw, the integral IS the area under the curve.

[JMEngineer]

Originally Posted by xfeejayx nobody said anything about same rpm.

Equal speed... Equal gearing... I'm pretty sure that means equal rpm

Originally Posted by xfeejayx and btw, the integral IS the area under the curve.

I'm well aware of what an integral is. The integral of a power or torque curve isn't helpful because the plot is in terms of rpm, not time or distance.

Work =/= Force * Time

[xfeejayx]

Originally Posted by JMEngineer Equal speed... Equal gearing... I'm pretty sure that means equal rpm I'm well aware of what an integral is. The integral of a power or torque curve isn't helpful because the plot is in terms of rpm, not time or distance. Work =/= Force * Time

I didn't say equal speed.

You can integrate with RPM homez

[06Speed6]

Why is this a debate lol.

I will say that in already produced vehicles in which gear ratios cannot be easily or cheaply changed, changing the torque curve is an effective option.

When I had a mustang it was easier and cheaper to regear than to change the power curve to match the gears, in this car its cheaper to change the power curve to match the gears.

All things being equal you are 100% correct, but things are rarely equal when comparing two different engines and most certainly two different vehicles.

[bigriver]

As long as I haz both hp and torque I'm happy. Oh, and some good brakes, lol.

[small_luffa]

I'm pretty I almost passed reading that.

[Atlanta]

I don't know man, Ice Cube didn't make a movie called HorsePower.....

[TRex]

this gets back to the whole point of the last discussion

THAT NEITHER POWER NOR TORQUE CAN BE LOOKED AT INDEPENDENTLY OF EACH OTHER (along with 100 other variables in what determines a car as "fast")

a statement such as power is most important is an ignorant statement (when discussing production vehicles)
a statement such as torque is most important is an ignorant statement (when discussing production vehicles)

your first statement JM of it is about the area under the curve is most correct but does not equate to power is most important

think of it in extremes

which is faster a car with infinite hp and 0 torque or infinite torque and 0 hp???

neither...they are both important and as 06speed stated the reason WHY torque isnt readily discussed is the fact that it is hard to directly change torque in production vehicles, so we always are adding more HP, but that is also giving us more torque in the end

some platforms CAN (through gearing...ask that guy with the protege that changed his gear ratios about it) affect their torque values and to them torque is directly more important than in our platform

[gbassrace]

Further Clarification:

FAQ: What is the difference between Horsepower and Torque?

I just sitting back and learning from all you guys here.

I have asked him: In the end, how do you make the car faster??? i.e.: less time from 30-130mph

[Tokay444]

Originally Posted by gbassrace Further Clarification: FAQ: What is the difference between Horsepower and Torque? I just sitting back and learning from all you guys here. I have asked him: In the end, how do you make the car faster??? i.e.: less time from 30-130mph

That wouldn't be making it faster.
That would be making it quicker.

[captain slow]

Originally Posted by Crarrs The real point of that should be that you're only making that peak 103 lb*ft at 0 RPM on the bicycle. Sure, that's a lot of torque, but once the bicycle starts moving and the angle of your crank moves, you're no longer applying that force to the full 175mm lever arm. BUt the CBR is making that lower torque at 10,000 RPM, all day, every day, and that's where the power component matters. Work over time. lb*ft/s^2

Oh snap!

Tapafuck

[MSMS3]

As stated by perhaps only one poster above, the real key to sustained acceleration, assuming equal gearing, is the "under the curve" torque in comparing one engine's power to another.

If maximum torque is below the point where the engine's rpm falls when shifting up to the next gear from your shift point, that seemingly high torque is "invisible" and useless to the engine.

Similarly, if maximum torque occurs too far to the right of the curve, performance is likely to be not so good, even if that is a high number. The engine that can produce high torque at the point in the power band where the rpm falls back to when WOT upshifting and that can maintain higher average torque through that gear, is the engine that will provide the strongest acceleration. Period.

HP is a function of torque and rpm and will, therefore take care of itself. Maximize the torque throughout the power band for best acceleration.

On the other hand, if absolute top speed, regardless of how long it takes you to get there is your goal, then tune to maximize torque, and therefore horsepower, at the highest rpm the engine can safely operate for its gearing, even if the hp curve looks peaky.

[rigor]

weight of vehicle also plays a huge role on how much tq is needed to acquire the fast, no tq in heavy car equals slow.............

[Bucker]

vs:



So, geared properly, what would happen?

[TRex]

top would win, hands down

[xfeejayx]

Originally Posted by Bucker vs: So, geared properly, what would happen?

Originally Posted by TRex top would win, hands down

wrong.

[TRex]

Originally Posted by xfeejayx wrong.

ahh really? =( iz sad

he did mentioned geared properly so yea you could argue that you could always gear one car to beat another


but actually i am not wrong....i know both of those cars are FWD, so i know the bottom one would lose due to lack of traction (=D) assume dig race of course

[xfeejayx]

Originally Posted by TRex ahh really? =( iz sad he did mentioned geared properly so yea you could argue that you could always gear one car to beat another but actually i am not wrong....i know both of those cars are FWD, so i know the bottom one would lose due to lack of traction (=D) assume dig race of course

the geared properly to me means optimize gearing in each car. JMENGINEER is right in that whoever puts more AVERAGE power down wins. In this case, the power would come from the increased engine speed.

Well, gear that down, and you end up with more wheel torque than the first car. It would take you a fraction of a second more in the second car to get to your high torque band, but once you're there, you have the advantage of the torque (about equal) but also of the lower gearing. you'd have to bang through more gears, but you'd have more wheel torque through it.

Originally Posted by freundb @TRex and @xfeejayx I need your debate skills. I agree with both of you but you guys seem to be able to take your thoughts and turn them into words and sentences. I fail at that.

real world experience does that to you. i can't generally throw around highly opinionated statements amongst engineers and have people believe them.






it does work sometimes though