How much HP do you have??

[Tommy]

Originally Posted by twin turbo

What about acceleration thru the gears?

Lots of people tend to think of horsepower as the UMMMPH that makes cars go. Therefore, they conclude that more horsepower results in quicker acceleration as well as higher top speed. And in casual conversation that's probably a good enough understanding. But technically, its an engine's torque that determines its rate of acceleration. Its possible (and sometimes desirable) to build two engines that produce similar amounts of torque, but at different points in the RPM range. The engine that produced its optimum torque higher in the RPM range would produce more power (horsepower), but it wouldn't necessarily be capable of accelerating more quickly. It would, however, be capable of pushing the same car to a higher theoretical top speed.

[Snake2998]

Originally Posted by Tommy

Lots of people tend to think of horsepower as the UMMMPH that makes cars go. Therefore, they conclude that more horsepower results in quicker acceleration as well as higher top speed. And in casual conversation that's probably a good enough understanding. But technically, its an engine's torque that determines its rate of acceleration. Its possible (and sometimes desirable) to build two engines that produce similar amounts of torque, but at different points in the RPM range. The engine that produced its optimum torque higher in the RPM range would produce more power (horsepower), but it wouldn't necessarily be capable of accelerating more quickly. It would, however, be capable of pushing the same car to a higher theoretical top speed.

That's actually wrong - it's horsepower or using another name for it "Rate of Work" that makes a vehicle accelerate quickly.

If you don't agree think of it this way - two identical cars geared for their rev range but with Identical torque - one a stump puller making peak torque at say 3000 revs hitting the limits of it's usable rev range at say 4500 rpm and the other making peak torque at say 5000 revs and peak horsepower at say 6000 revs racing down the drag strip. Which do you think will win. You're wrong if you think it's the stump puller - if you don't agree try feeding the figures into a drag simulator and you will see why horsepower matters.

[Tommy]

Snake2998,
We may have to agree to disagree on this one. ... In my comments to twinturbo I was speaking of instantaneous acceleration rather than a race in which acceleration is one of several factors that determines the winner. A drag race is partly about the torque required for acceleration, but also about the power required to push the car against the ever increasing wind resistance. .... I would argue that if you were racing from 30 to 70 MPH you should choose the engine with greater torque regardless of its horsepower. But if you are racing from 70 to 150 MPH, choose the engine with the greater horsepower. ... Newton's 2nd Law of Motion says that the acceleration of an object is proportional to the force applied to it. And the force applied to a car by its engine is torque, not power.