friction horsepower

engineering

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Last updated

June 26, 2026

Quick Summary

Friction horsepower refers to the power lost within an engine due to the friction between its moving parts. This power loss is a significant factor in an engine's overall performance.1

Friction itself is a force that opposes motion when solid objects slide or roll over each other. In automobiles, approximately 20 percent of engine power is used to overcome friction in moving components. This friction arises from the attractive forces between surfaces and the physical interaction of microscopic irregularities.2

The power developed in an engine's combustion chambers is greater than the power delivered to the output shaft (brake horsepower) because of these mechanical losses, including friction. The difference between the power developed in the cylinders (indicated horsepower) and the delivered power is the friction horsepower. This loss can be evaluated by "motoring" the engine, which means driving it with a dynamometer without burning fuel.3

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gasoline engine
Performance
This power loss, called the friction horsepower, can be evaluated by “motoring” the engine (driving it in a forward direction) with a suitable dynamometer when no fuel is being burned. The power developed in the cylinder can then be found by adding the friction horsepower to the brake horsepower. This…
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This power loss, called the friction horsepower, can be evaluated by “motoring” the engine (driving it in a forward direction) with a suitable dynamometer when no fuel is being burned. The power developed in the cylinder can then be found by adding the friction horsepower to the brake horsepower. This…
Read More