Quote:
Originally Posted by Destructicon
More torque = faster pick up and acceleration. HP is all about maintaining that momentum.
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Not ture. Ever wonder why highly-tuned high-revving cars put alot of HP, but so little torque (2ZZ-GE, K20 etc.) at the crank, yet they are much quicker than many cars with substantially more torque?
HP is the measure of work the engine does while torque is the resultant twist generated from the engine. They are correlated and not independent. Granted, weight is the biggest factor that determines how well the power is utilized, the engine HP, torque and total transmission ratio determine how much torque will be generated to the wheels.
In automotive engineering, the equation looks like:
Total wheel torque = Total crank torque x Total transmission ratio (final drive, gear ratios etc.)
The shorter the gearing, the higher the torque will be to the wheels. However, you cannot put very short gearing on a car that puts out no meaningful power after 5000 rpm so it usually ends up with tall gearing in order to keep the revs as much possible in the midrange (around 3500 - 5000 rpm) and relies more on torque generated by engine.
A high-revving engine on the other hand, relies less on crank torque, but more on short gearing and final drive to generate wheel torque since the entire rev-range is so big (around 8000 rpm) where HP and tuning allows for a very flat torque curve that short gearing works to it's advantage.
The downside? With a highly-tuned and high-strung engine with transmission ratio designed for best acceleration using the entire rev range hurts daily drivability.