Fix_Until_Broke said:

HP = (Torque * RPM)/constant of your choice

Constant of your choice?!?! Do you think they just plucked a number out of space? The number

**must** be 5252 if you want to convert torque to HP. There is a long equation as to how this number was reached and you can find it on the internet, but I don't really think we need to go into that...

Originally Posted by

**jackbombay, a question that he REALLY wants JNECR to answer, pretty please **
* You are drag racing, if you loose the drag race you will loose your job and your house, obviously there is a huge incentive for you to win, at what RPM will you shift your car? Assuming of course you are driving a pre 2003 5 speed VW TDI.*

Well?

Right around 4700RPMs...

So with that mainly unrelated question out of the way..

The original question that we are now discussing is:

**Is a TDIs instantaneous acceleration higher at 1900RPM or at 3500RPM?**
We can reword this in mulitple ways:

Will a car's instantaneous acceleration be higher at it's HP or torque peak?

Will a car's longitudinal acceleration plot mirror it's torque dyno curve or it's HP dyno curve?

I finally found a good example to show my side of the discussion (not argument, mind you..

):

So we'll go to number 3 on the wording, "will a car's longitudinal acceleration plot mirror it's torque dyno curve or it's HP dyno curve?"

Well.. there's a very simple conclusion if we examine how a dyno works in the first place.

What does a dyno really measure?

The fact is there is no way of directly measuring power - all types of dynamometer measure torque and then power is calculated from the formula BHP = Torque (ft/lbs) x rpm/5252.

A Dyno measures the force put on the rollers.

**F=ma (Force equal mass * acceleration)**
Force on the rollers is therefore the roller mass multiplied by the acceleration. This force is multiplied by the radius of the roller itself to give torque at the wheels using the following equation:

T = Fr

Where T is torque; F is force; r is radius of application

Therefore we can easily show that acceleration is directly related to torque because, after all, that is how we arrive at the torque curve to begin with.

If it were the other way around (HP related to acceleration) we would directly measure HP on a dyno and have to have an equation similar HP = Tq*RPM/5252.

So have I made my point? If I haven't I will be more than pleased to explain this again in a different example, just gimme time to think of one... But in reality I think this is probably the best one I'll ever come up with.