I have worked on equipment most of my life and still don’t understand.
nearly all energy put into an ice engine that isn’t lost as heat goes to spinning a shaft. please explain to me how i can tell the difference between torque and horse power?
In: Physics
Horsepower is a unit that measures the rate of work produced by an engine. Torque is its actual power or “strength”. Why don’t we just use torque then? Because just the torque number doesn’t tell the whole story, but horsepower, though abstract, can actually tell you more about what to expect from an engine. Lack of toque can be made up for by making an engine work faster to apply its less torque more rapidly.
An easy and intuitive way to understand this is a simple example with a bicycle. Disregard gears for now, let’s assume it’s fixed gear. We’re concerned with the crank, the pedals. You as a rider can only push so hard down on the pedals. The maximum downward force you can apply with your legs is basically your maximum torque (measured at the crank of course and not just on your downward stroke, just like in engines the power is measured at the crank not the pistons). So let’s say you’re trying to pedal as hard as you can and as fast as you can. First you’ll reach your maximum torque because you can start applying all your force at any time and keep it there (disregard fatigue). But just because you are applying your maximum torque, it doesn’t mean you can’t do it faster, so you keep applying maximum force while pedalling faster and faster, this rate of applying the force is the horsepower. Eventually, as anyone who has tried to ride a bicycle really fast can tell you, you will reach a point where you cannot physically go faster, and even with the aid of a slope the pedals start moving out from under your feet faster than you can push down. You’re now at your maximum horsepower, and something similar happens with pistons which is why all dyno charts always have a small drop off after peak HP. It’s also why torque is initially higher but then horsepower takes over.
So by knowing an engine’s torque and horsepower I can intuitively assess its overall capabilities and performance. I know for example that a pickup truck with 200HP and a city car with 200HP will both be able to tow a trailer, but due to their difference in torque I’d prefer to use the pickup and tow at a leisurely 2,5k rpm rather than get the city car and drive around at 6k rpm constantly for the same task. Conversely for a track car I will prioritise high horsepower because I know that gives me a better track experience by having a fast revving car that can punch out of corners and blast down the straights without wasting time spooling up or running out of juice early.
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