The "brake" in brake horsepower is a piece of history that survived into the spec sheet. Engine power was measured by loading the engine with a brake and reading how hard it worked against it, and the name of the apparatus stuck to the number it produced. What it describes is a location as much as a quantity: the reading is taken at the crankshaft, with the engine on its own, rather than at the wheels of a finished car.
That is the useful part. Every mechanical link between the engine and the road surface absorbs some of what the engine makes, so a figure quoted at the crank is always larger than the power that actually reaches the tarmac. Two cars with the same brake horsepower can put noticeably different amounts of it down.
The underlying unit is ordinary horsepower, and BHP only specifies how it was arrived at. We haven't been able to read a standards body's own wording on the test conditions, so this page describes the principle and stops there rather than quoting a procedure it can't source. For the other half of the spec sheet, see torque, and for why the two aren't interchangeable, the comparison.
Written by Craig Fearn, Petrol & Ink. Last updated .