A Simpler Explanation Of The Measurement Of ONE HORSE POWER
One horsepower equals 550 foot pounds (pound feet) per second. In high school, in physics class, I generated 1 horsepower by running up a flight of stairs. :) Housted
Forum Discussion
turbojimmy wrote:larry cad wrote:
Torque is constant over the RPM range, while Horsepower is a straight line function of RPM. Thus, the diesel engine, which operates with a typical limit of 2400 RPM produces more torque than a typical gas engine which operates up to 5500 RPM. Another factor that produces torque is larger displacement (BIG pistons)
The formula for HP is torque * RPM /5252, so HP is a function of RPM and torque. Torque is not constant over the RPM range of any engine. This is why people talk about "torque curves" of engines. Although electric motors have near flat torque curves (which is why train locomotives are diesel/electric). Diesels deliver torque more consistently through the RPM range compared to gasoline engines. But, there's a curve - torque delivery is not a constant. Since diesel engines don't rev as high their horsepower is relatively low (RPM is a variable in the HP calculation) when compared to a gasoline engine because the gasoline engine can produce 2 or 3 times the RPM.
The formula is correct. The problems always come from interpreting the formula. I work with electric motors which operate differently than "engines" in that motors have a zero rpm state while engines have an idle state. Electric motors at zero rpm can produce their maximum torque, while engines have to be rotating, even at idle to produce torque unless you consider the starter motor :). Keep in mind that in physics, torque is not work. No work is done by an electric motor at zero rpm, but it still can produce rated torque. To use this formula for electric motors, you have to use manufacturers nameplate RPM and rated HP. Rated HP is only available at nameplate RPM and tapers off in a straight line to zero RPM.
