Bill@ROUSH

Perhaps the most used term in describing a vehicle's performance is horsepower. In this article, we'll dive into what exactly this term means, how it compares to its companion term "torque," and how we can best look at these to glean insight into real usable performance.




The Definition of Horsepower
The term "horsepower" has been around for quite a while. In 1702, Thomas Savery made reference to the potential work that a horse can do as a measurement of power. In his book The Miner's Friend he writes, "So that an engine which will raise as much water as two horses, working together at one time in such a work, can do, and for which there must be constantly kept ten or twelve horses for doing the same. Then I say, such an engine may be made large enough to do the work required in employing eight, ten, fifteen, or twenty horses to be constantly maintained and kept for doing such a work..."
James Watt later made reference to the potential work that a horse can do (horsepower) as a way to market a new and improved steam engine. He determined that a horse can do 33,000 foot-pounds of work in one minute (the equivalent of pulling one pound of weight 33,000 feet in distance).


The Definition of Torque
Torque is the tendency of a force to move around a point. In other words, torque refers to twisting force. The unit of measure for torque that we all know, the "ft-lb," "lb-ft," or "foot-pound" is the amount of turning force applied to move one pound a distance of one foot around an axis at a radius of one foot.
So, one full rotation around an axis at a radius of one foot with one foot of resistance yields the following amount of work:

work = (2 * pi) * 1 lb-ft = 6.2832 lb-ft




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