I took college physics. I learned that power is unit work per unit time, which can be expressed as newton-meters per second. Torque is a cross-product quantifying rotational force accounting for a lever arm, which is expressed as newton-meters. I know that the distance in the measurement of torque is perpendicular to the direction of rotational motion whereas the distance in measuring power is parallel to the direction of motion, so these are not the same “meters” at all. But both of these involve a measure of force – more force means more power and it means more torque. However, when it comes to car engines, two engines can have the same horsepower but very different torque. Why do HP and torque not increase in lock-step? Is this just a matter of available gear ratios in the transmission? Or is there a way to build an engine deliberately to make torque vs. Deliberately to make horsepower independent of the transmission? Thanks!
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Horsepower and torque are related. You an convert one to the other with a few other factors.
Engine torque is proportional to horsepower/engine rpm. So engine torque is effectively how much power you get out of a single engine cycle, where horsepower is how much total power you get in a minute.
The transmission comes into play when talking about power at the wheel. Think of a large truck with a wide gear ratio – it can go into a very low gear to ‘concentrate’ that power into a single rotation of the wheel, or a higher gear to turn the wheel faster. You lose some power due to system inefficiencies, but you’re otherwise running that problem backward by using the transmission to measure how much torque there is off of the wheel, rather than how much torque is being applied to the drive shaft by the engine. The latter isn’t changing as you shift gears, but the former is.
Engine torque does vary based on the engine RPM because of the rate at which the pistons are firing, valves are opening, fuel mix, temperature, etc. shifts the efficiency of the engine causing torque to vary – lower at low and high RPM and higher at mid RPM. This is a sort of efficiency of an engine to generate power. Really good engines (racing cars) are more consistent at generating torque across engine RPM than less good engines (your car).
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