Horsepower vs. Torque

Horsepower vs. Torque
When cars or engines are tested they usually list the horsepower and torque. We will explain what these two numbers are and how they affect the performance of the car.
Torque is a measurement of the twisting force that an engine creates. Imagine a one foot long crank attached to a shaft. You then grab the handle of the crank and pull on it with 50 pounds of force. You have just created a twisting force on the shaft of 50 foot pounds.
Then imagine putting a pulley on the shaft and wrapping a rope around the pulley and hanging a 25 pound weight on it. Now when you pull on the handle of the crank the weight raises up. Now you have done some “work” by moving the weight. The measurement of this work is called horsepower.
To summarize, torque is a measurement of force and horsepower is a measurement of work. I will try to explain how this affects the performance of a car. The more horsepower and torque an engine has the faster the car may be. Just as important is “shape” of the horsepower and torque “curve”.

hp vs. torque 2

The graph shows two different engines with very different power curves. The blue engine has more peak power than the red one but will be much more difficult to drive on an oval track or road course. The maximum power of the blue one is available in a very narrow rpm range. The diver is then forced to keep it in that narrow range to get the best performance.
It is very common on a road course or oval track with tight corners to have the rpm drop to 3,000 rpm. The red engine will accelerate the car more quickly than the blue one because it has more power at that rpm. The lap times of the red engine will probably be quicker than the blue one. It will certainly be easier to drive.
The blue engine would probably work well in a drag race car that operates in a narrow rpm range.
Go to http://youtu.be/fgLNO3ThGD4 to see a very well done video explaining horsepower and torque.