Quote:
Originally Posted by 42pilot
This is not completely correct either. I can tune a motor with more torque and not affect horsepower, by where I apply the torque.
For example:
300 lb ft of torque at 5000 rpm is 285 hp
500 lb ft of torque at 2000 rpm is 190 hp
But the last tune (car) will break the rear tires lose and I will beat the higher hp car big-time in a short drag race, like from one light to the other. At higher rpm's and over a longer drag race the higher hp car will win because hp is the amount of work done over time (think 1/4 mil times, which is a useless unit of measure for modern street cars with access to so much torque). For street applications, take the higher torque every time because the power is 1000 rpm off idle whereas the other car has to get to 5000 rpm to get the benefit of the full torque. The first car above has a long linear power curve and the second car has an alpine curve, nearly vertical, from the start.
For cruising, torque is also more important than a big hp number. Look at large highway trucks with 12L motors putting out 475 hp and 1700 lb ft of torque. Granted the rpm curve is flat, but who cares when cruising with 6-8 speed tranny's.
Now, for the track, big torque over a lot more usable rpm (which means high hp) in lightweight cars, carefully engineered in the power curve (transmission and rear-end combo's), win races.
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It's far more meaningful to look at the torque / power at the driven wheels rather than the crankshaft - so that the whole 'power train' is considered...
