Torque & Power

[8400rpm]

Guys (& girls)

There seems to be a few people on this form making statements about this topic without really understanding what they are talking about. :( So I thought I might try to clarify the meaning and realtionship between power and torque, if anyone is interested read on.

Torque is the amount of twisting force an engine generates, or how strongly it can twist the crank shaft.

Power is the amount of work and engine can do in a given amount of time.

Talking conceptually Power = Torque x RPM

Often you hear people say that it is torque that determine how hard a car can push you in the back under acceleration and this is ture tue a certain extent. Is what people fail to appreciate is that it is torque at the wheels that determines how hard a car can accelate (also weight needs to be factored in, but we will come to that later). Is what needs to be considered is the role of gearing.

With a gear box the amount of power you put in is the same amount you get out the other side (excluding any loss due to gear box efficiency). A gear box is about trading torque for rpm. So you can get more torque out the other side at a reduced RPM or more RPM out the other side with a reduced torque.

So to give an example, lets say you have 2 cars one is a commodore travelling at 50km/h with the engine at 3500RPM making 300Nm of torque. The other is a corolla sportivo travelling at 50km/h with the engine at 7000RPM makeing 150Nm of torque. For this to occur the overall gear ratio (gear box & diff) of the corolla is double that of the commodore. The gear box in the corolloa is trading RPM for torque at twice the rate of the commodore. Thus both cars have identical amount of torque at the wheels at identical wheel RPM, and thus (assuming the cars weighed the same) would accerate at the same rate or push you in the back with the same force.

So is what determines how hard a car accelerates is torque on the road divided by weight, and torque on the road is more directly related to power (as this considers both toque and RPM) than torque alone.

So to put this into persepective. The reason why relatively low torque engines like that in the corolla sportivo can give stong acceleration is that they can make torque at such a high RPM that you get lots of power that can be geared down to give lots of torque at the wheels (remember power = torque X rpm).

So that's it.

I hope it was informative and/or helpful. B)

[shaohaok]

http://au.toyotaownersclub.com/forums/inde...howtopic=866&hl

[Doctony]

brief and informative :) :) :)

keep u the good work, man

[xoom]

Now im going to steal someones quote by saying this but to summarise it even further:

"Torque gets u there... Power keeps u there"

[DANZZT231]

Tourqe wins the street, Horsepower wins the race and dyno :P

[ghost]

well said!