What exactly is a horsepower?

Question

I went to wikepedia and read the stuff still don't get it. Does it refer to how quickly an engine can burn fuel and therefore how fast it can go? Or is it more how quickly it can go fast? Is there really a difference?

Answer 1

Neither. Horsepower doesn't refer to speed. A big rig diesel truck can have a lot more horsepower than any car, yet it's not as fast. In general, the more horsepower an engine has, the less fuel efficient it is. Kind of like feeding real horses!

Horsepower is derived from how many horses it takes to lift a weight for a sustained period of time. The more horses, the better you are able to sustain the lifting power.

In cars, a higher horsepower also gives you a better ability to sustain torque. Torque is what applies the pressure on the driveshaft that , via gears, applies a forward pressure to the drive wheels of the vehicle. You do not need high horsepower to have high torque. But unless you're going down hill, it sure helps.

Look at it a differently. Imagine using your hand to tighten a bolt. You can apply about 8 lbs of torque to the bolt. Now, put a 10 inch wrench on the bolt, and you can apply about 20 lbs of torque. Now, use an 18 inch wrench, and you can apply about 80 lbs of torque. You see, you haven't gotten any stronger. Torque is the arm. Horsepower is the strength to push the arm.

Answer 2

To understand horsepower, you have to understand torque. Torque is turning force. The more torque to turning force you are applying. If you have a stuck bolt and you try to turn it with a longer wrench you can apply MORE torque.

Horsepower is calculated by

HP = torque * RPM / 5252.

In general you get more HP (for the same torque) if the torque curve is better spread out over the RPM range (and into higher RPM).
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Think of Torque as the "off the line" accelerating power.
Think of Horsepower as the passing other car power (once the car get moving).

Answer 3

And how big is that horse? Torque and Kilowatt output is much better way to display the work a engine can do. Horsepower is a ancient term and we need to think metric anyway. Look up Newton Meter as it pertains to work output