How is horsepower of an engine rated????

Question

When we are told of the power of an engine which is rated in horsepower, how is this determined and what is one horsepower equal to??

Answer 1

One horsepower is equal to slightly more than 745 Watts.

The term 'horsepower' is seldom used in scientific discussion because of the varying methods, definitions and types of ratings (brake horsepower, actual horsepower, net horsepower, etc.)

Unfortunately - and I assume to are talking about vehicle manufacturers - horsepower ratings over the years have fallen prey to insurance surcharges and racing class determinations (both of these lead to lower published horse power ratings from the manufacturers) and Madison Avenue marketing of sports cars (which sometimes lead to higher published ratings from the manufacturers.)

The only true indication of actual 'usable' horsepower is at the rear wheels - and that can be determined on a dyno designed just for this purpose.

Answer 2

Engine HP (also called brake-horsepower) is measured with a dynamometer. Essentially the operator puts a higher and higher load (through friction braking) on the engine, until the engine stalls. The operator is allowed to adjust RPM or fuel to try to keep the engine turning. The more friction braking the engine takes, the higher the horsepower. In a way it's like using successively heavier drags in tractor pulls.

See the source for an in-depth article.

Answer 3

One horsepower is equal to 33,000 ft lbs per minute of work.

Horsepower is a ratio between a force producing work and a rate of producing that work.

In a engine it will be a ratio of torque to rpm. For hydraulics it will be a ratio of pressure to flow.

Most systems that have a motor, or engine, will give a horespower rating so you can determine it's output. You might want to know what RPM can be achieved with a specific torque load or any other variation.

Answer 4

550 Lb ft/sec. Means if you can lift 550 lb to one feet height in one second your power is one horse power.If I remember correctly HP can be calculated from engine's swept volume it is indicated on every car even in motocycle. 1.2litre, 1.5 litre for car and 125 cc, 250 cc for motocycle.
Hope this will help.

Answer 5

HP=CP=75kgf m/s

Answer 6

http://www.dsm.org/tools/calchp.htm
http://www.web-cars.com/math/horsepower.html
http://auto.howstuffworks.com/horsepower.htm

should cover it pretty well