Which is faster horsepower or torque?

[Andy M]

Two identical cars in weight, layout, engine capacity and layout, body design etc with the same type of gearbox (but different ratios bespoke to their respective engines), which would be quicker over 1/4 mile:

A car with 600bhp and 400lb/ft?

Or a car with 400bhp and 600lb/ft?

[anonymous-user]

When is this torque available and what rev range can I have ax power?

[Zad]

Mathematically, you can only generate acceleration with power. Torque is just an abstraction of that.

[Monty Python]

The one with 600bhp.

With that power and a weight of 1500kg, you'll do the standing quarter in ~11.4 seconds. With 500bhp it'll take ~12.5.

[Andy M]

Topbox said:

When is this torque available and what rev range can I have ax power?

Both gearbox and engine on each vehicle is tuned for maximum acceleration efficiency over the 1/4 mile.

[s p a c e m a n]

Are either of them on a conveyor belt?

[tvrolet]

Horsepower is Torque x RPM / 5252

Therefore the 2 options of power/torque can only occur at a certain RPM each. So based on the above then RPM = Horsepower x 5252 / Torque

So the 400Hp/600ft/lb motor is making its figures at 3501 RPM
The 600hp/400ft/lb motor is making its figures at 7878 RPM.

But of course the gearbox acts as a torque multiplier, so to get the same output shaft speed the 600hp/400ft/lb motor is geared down by 2.25 to get a 3501 output shaft speed - thus it's making 400ft/lb x 2.25, thus 900 ft/lb...which is 50% more than than the 600ft/lb motor can make at the shaft at 3501 RPM

Ergo the 600Hp/400ft/lb is 50% faster, at a particular instance - all other things being equal.



can I add I actually have 630 ft/lb?

[Huntsman]

Zad said:

Mathematically, you can only generate acceleration with power. Torque is just an abstraction of that.

Mathmatically you failed.

[tvrolet]

doogz said:

tvrolet said:

Horsepower is Torque x RPM / 5252

Therefore the 2 options of power/torque can only occur at a certain RPM each. So based on the above then RPM = Horsepower x 5252 / Torque

So the 400Hp/600ft/lb motor is making its figures at 3501 RPM
The 600hp/400ft/lb motor is making its figures at 7878 RPM.

But of course the gearbox acts as a torque multiplier, so to get the same output shaft speed the 600hp/400ft/lb motor is geared down by 2.25 to get a 3501 output shaft speed - thus it's making 400ft/lb x 2.25, thus 900 ft/lb...which is 50% more than than the 600ft/lb motor can make at the shaft at 3501 RPM

Ergo the 600Hp/400ft/lb is 50% faster, at a particular instance - all other things being equal.



can I add I actually have 630 ft/lb?

Wait, what?

You're assuming it's making peak power and peak torque at the same time?

Nope. The description was that motor 1 makes 400hp and 600ft/lb. This is ONLY mathematically possible at 3501RPM. It may or may not be peak power. It may make more or less power at higher or lower RPM, but for the condition of 400hp concurrent with 600ft/lb that this can ONLY happen at 3501 RPM

The description was that motor 2 makes 600hp and 400ft/lb. This is ONLY mathematically possible at 7878RPM. It may or may not be peak power. It may make more or less power at higher or lower RPM, but for the condition of 600hp concurrent with 400ft/lb that this can ONLY happen at 7878 RPM.

Therefore for the power/torque stated (and no-one said this was peak power) these can ONLY happen at 3501 and 7878 RPM respectively. End of. Do the maths.

And thus for the motors making that power to drive an output shaft at the same speed the 7878RPM motor has to be geared down by 2.25.

None of this is guesswork or requires any assumptions. For the power/torque figures stated this is how it works. Put in different hp/torque combinations and they to can ONLY be achieved at a specific RPM. It is simply not possible to have the same torque at the same RPM and make a different horsepower figure.

[VBRJ]

Owner of petrol car: "Power"

Owner of diesel car: "Torque"

Typical PHer: "Potato"

[kambites]

Peak power and peak torque are irrelevant.

The important figure (once you're moving fast enough to be a decent distance up the rev-range in first gear) is the greatest possible definite integral of the power curve over the difference in revs between any two adjacent gears.

[GroundEffect]

Zad said:

Mathematically, you can only generate acceleration with power. Torque is just an abstraction of that.

You've got that backwards.

Torque actually produces a force at the road. Power is the abstraction of that to allow comparison.

A car with more BHP (and everything else equal such as grip, weight, drag, CoG etc etc) will be faster in ideal conditions. It gets a bit more complicated when you include a squishy human in the middle and you need to consider driveability.

OP, in your example, the 600BHP car will be noticeably faster.

[McWigglebum4th]

Andy M said:

Two identical cars in weight, layout, engine capacity and layout, body design etc with the same type of gearbox (but different ratios bespoke to their respective engines), which would be quicker over 1/4 mile:

A car with 600bhp and 400lb/ft?

Or a car with 400bhp and 600lb/ft?

Okay lets ask another question

What is faster

My wives fiat panda which produces about 80lb/ft of torque at 5000rpm


Or a scaffolding pole which is lighter then the panda by about 800 kgs but it produces with me hanging off the end well over 1000lb/ft of torque at zero rpm

[Welshbeef]

tvrolet said:

Nope. The description was that motor 1 makes 400hp and 600ft/lb. This is ONLY mathematically possible at 3501RPM. It may or may not be peak power. It may make more or less power at higher or lower RPM, but for the condition of 400hp concurrent with 600ft/lb that this can ONLY happen at 3501 RPM

The description was that motor 2 makes 600hp and 400ft/lb. This is ONLY mathematically possible at 7878RPM. It may or may not be peak power. It may make more or less power at higher or lower RPM, but for the condition of 600hp concurrent with 400ft/lb that this can ONLY happen at 7878 RPM.

Therefore for the power/torque stated (and no-one said this was peak power) these can ONLY happen at 3501 and 7878 RPM respectively. End of. Do the maths.

And thus for the motors making that power to drive an output shaft at the same speed the 7878RPM motor has to be geared down by 2.25.

None of this is guesswork or requires any assumptions. For the power/torque figures stated this is how it works. Put in different hp/torque combinations and they to can ONLY be achieved at a specific RPM. It is simply not possible to have the same torque at the same RPM and make a different horsepower figure.

What about scenarios where the engine has had its torque limited so that it doesn't break the gearbox could you then have the same torque over a long rpm range but increasing power.

[tvrolet]

XJ Flyer said:

It's going to be a st engine that can only make 400 hp from a torque peak of 600 lbs/ft.LOL

Do the question again this time which is faster a car with 600 lbs ft peak torque and 600 hp peak power or a car with 400 lbs ft and 600 hp.It's all about the amount of torque and how flat the torque curve is either side of peak torque from which we can deduce average power and hence acceleration.

Edited by XJ Flyer on Monday 13th January 20:41

Christ on a bike, does no-one actually understand this stuff?

Your 600hp/600ft/lb motor can ONLY make that at 5252RPM. Not higher revs, not lower revs, but 5252RPM.

The 600hp/400ft/lb motor HAS to be turning ar 7878RPM, thus is it effectively making 1.5 times the power at the end of the gearbox.

Shall we try this again kids. All together now...

TORQUE IN MEANINGLESS UNLESS YOU CONSIDER THE RPM
TORQUE IN MEANINGLESS UNLESS YOU CONSIDER THE RPM
TORQUE IN MEANINGLESS UNLESS YOU CONSIDER THE RPM
TORQUE IN MEANINGLESS UNLESS YOU CONSIDER THE RPM
TORQUE IN MEANINGLESS UNLESS YOU CONSIDER THE RPM

Got it. Now try this one...

FOR A GIVEN TORQUE AND RPM THE POWER IS ALWAYS THE SAME (TOURQUE x RPM / 5252)
FOR A GIVEN TORQUE AND RPM THE POWER IS ALWAYS THE SAME (TOURQUE x RPM / 5252)
FOR A GIVEN TORQUE AND RPM THE POWER IS ALWAYS THE SAME (TOURQUE x RPM / 5252)
FOR A GIVEN TORQUE AND RPM THE POWER IS ALWAYS THE SAME (TOURQUE x RPM / 5252)
FOR A GIVEN TORQUE AND RPM THE POWER IS ALWAYS THE SAME (TOURQUE x RPM / 5252)

Lets consider a motor with the flattest torque curve in the world and it makes 10,000 Ft/lb

But it makes it at 10 RPM, so the power is under 20hp. So your 10,000ft/lb flat-curve motor will be accelerating slower than a 2CV.
So much for torque being the thing that makes cars go.

Jeez

Ah'm oot.

[steveT350C]

tvrolet,

I'm with you!


I prefer the 'black is the fastest colour' discussion myself. More bullst, less physics!

[Monkeylegend]

tvrolet said:

Christ on a bike, does no-one actually understand this stuff?

Your 600hp/600ft/lb motor can ONLY make that at 5252RPM. Not higher revs, not lower revs, but 5252RPM.

The 600hp/400ft/lb motor HAS to be turning ar 7878RPM, thus is it effectively making 1.5 times the power at the end of the gearbox.

Shall we try this again kids. All together now...

TORQUE IN MEANINGLESS UNLESS YOU CONSIDER THE RPM
TORQUE IN MEANINGLESS UNLESS YOU CONSIDER THE RPM
TORQUE IN MEANINGLESS UNLESS YOU CONSIDER THE RPM
TORQUE IN MEANINGLESS UNLESS YOU CONSIDER THE RPM
TORQUE IN MEANINGLESS UNLESS YOU CONSIDER THE RPM

Got it. Now try this one...

FOR A GIVEN TORQUE AND RPM THE POWER IS ALWAYS THE SAME (TOURQUE x RPM / 5252)
FOR A GIVEN TORQUE AND RPM THE POWER IS ALWAYS THE SAME (TOURQUE x RPM / 5252)
FOR A GIVEN TORQUE AND RPM THE POWER IS ALWAYS THE SAME (TOURQUE x RPM / 5252)
FOR A GIVEN TORQUE AND RPM THE POWER IS ALWAYS THE SAME (TOURQUE x RPM / 5252)
FOR A GIVEN TORQUE AND RPM THE POWER IS ALWAYS THE SAME (TOURQUE x RPM / 5252)

Lets consider a motor with the flattest torque curve in the world and it makes 10,000 Ft/lb

But it makes it at 10 RPM, so the power is under 20hp. So your 10,000ft/lb flat-curve motor will be accelerating slower than a 2CV.
So much for torque being the thing that makes cars go.

Jeez

Ah'm oot.

You're out you say I was never in

Know anything about knitting?

[Patrick Bateman]

doogz said:

No, please, explain how an engine that makes 600bhp and 400lbft could be making that peak torque at 2000rpm, with 152bhp, and 600bhp at 10,000rpm with 315lbft.

It'd be an unusual engine, but it's just a set of figures I picked.

Ah, someone who doesn't refer to torque as lbs/ft or ft/lbs, finally.

For what it's worth, talking about the 2 as if they're unrelated is off to the wrong start right away.

More torque = more horsepower. Of course without an rpm the torque figure doesn't mean much.

[MethylatedSpirit]

The one with the largest area under the torque curve wins


End of

[Welshbeef]

Torque is meaningless without revs

Torque = "Work"
Power = the rate of work.