Brake horsepower is a measure of the developed power of an engine in actual operation.

• A. The maximum power at redline
• B. The power developed when engine is idling
• C. The developed power of an engine in actual operation
• D. The theoretical power without losses

Answer: (C)

Brake horsepower measures the power an engine actually develops while it’s operating under load. It’s the real output the engine provides at the crankshaft, measured with a brake dynamometer, reflecting what the engine can deliver to do work under test conditions and during normal operation. This value accounts for internal engine losses such as friction and pumping losses, so it’s different from the peak power you might see at redline (a maximum, under specific rpm), from power at idle (which is very low), or from theoretical power without losses (theoretical or indicated power). Because it describes the engine’s power in actual use, the statement is the best description.