Horsepower...clarify please.

Dear Car Talk

Dear Car Talk | Apr 01, 1992

Dear Tom and Ray:

The guys at the watering hole are ready to fight over this one. One group believes that when you see "400 HP," that refers to the size of the engine. The other group says that the horsepower is measured by the power at the wheels. We've all agreed that your words are law. Help us out.

RAY: As in most fights that break out between two parties at a bar, Harry, you're both wrong.

TOM: Horsepower is the amount of power produced by the engine, measured at the end of the engine's crankshaft--before the power goes to the wheels. And it's related to engine size, there's no exact correlation.

RAY: Right. While you could probably guess that the 5.0 liter engine in the Ford Mustang has more horsepower than the 1.3 liter engine in the Ford Festiva, there are others you probably couldn't guess. For instance, which has more horsepower? The 3.0 liter engine in the Ford Taurus or the 3.0 liter engine in the Mazda 929?

TOM: It turns out that the Taurus engine puts out 150 horsepower, while the Mazda engine, which has the same displacement, produces 190!

RAY: And the difference has to do with things like the cylinder bore and stroke, the compression ratio, the number of valves per cylinder, and stuff like that.

TOM: So I'm glad we had this opportunity to save a few barstools, Harry. Feel free to write to us again at the first sign of potential conflict.

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