Peak power tends to follow peak torque on our engines because they have highest volumetric efficiency usually in the midrange. However, the gain from higher RPM is greater than the loss from reducing torque until you reach the peak power point.

Torque at the wheels does indeed vary with gearing * , but commonly torque and power as manufacturers usually quote them are referred to at the flywheel - before the gearbox and out of the car.

* hence why Honda afficionados will quite correctly tell you that the shorter gearing with higher rev limits can give the same or better acceleration in gear despite torque figures that whilst excellent for their capacity are apparently poor compared with their forced induction or larger capacity competitors.

Another way of thinking about your original question:

Work = Force * Distance (Torque in other words)
Power = Work / Time (more power if you can do that work in a shorter time - ie more power with the same torque at higher RPM)

Hope I've not upset any physicists

[Edited by john banks - 11/2/2003 10:48:02 PM]

 

Since the subject came up, this is something i've been wondering about for a while...

If torque, (i assume measured at the flywheel) in Nm is the twisting moment of the shaft(the ability to resist a braking force?).

And power is the engine output in BHP (as in the ability to accelerate the flywheel).

How come the peak torque can be reached at a lower rpm than peak power?

And given it's the twisting moment,How come torque is not affected by which gear you are in and the weight of the car (ie using the momentum of the car as flywheel effect)?

I assume RPM plays an important role in this but i keep adding 2+2 and ending up with 5.

Am I missing something really simple here or has this got a few minds ticking over.

Cheers, Dave.

 

 

I could have guessed who'd answer this one, cheers john that's cleared up a few things.