Category: Technology and Terminology

Explanations of various automotive terms and the technology under the hood.

Doing the Twist: Horsepower, Torque, and Automotive Performance

One of the most confusing (and frequently contentious) questions in the automotive realm is the difference between horsepower and torque. You may have heard any number of pithy expressions, like “horsepower sells cars, but torque wins races,” or fans of big-engine muscle cars complaining that 200-horsepower four-cylinder engines are “gutless.” Surprisingly few of the worthies who throw around comments like that, though, are actually able to define the difference. What IS the difference between horsepower and torque, and what effect do they have on how a car performs?

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Understanding Gross Versus Net Horsepower Ratings

There are a lot of misunderstandings among car enthusiasts and historians about vintage horsepower ratings. It’s easy to assume from a casual glance at ads or spec sheets that even quite ordinary American family sedans of the sixties were overwhelmingly powerful, with 300 horsepower or more, and yet by 1975, many of those same cars were down to 150 hp or less. When asked the reason for the huge difference, gearheads tend to shake their heads and mutter about emissions controls and anemic, low-octane unleaded gasoline — which is true, but only partly.

What complicates the issue and makes apples-to-apples comparisons difficult is the fact that those pre-smog horsepower ratings were not calculated in the same way as modern engines. “A horsepower is a horsepower, right?” you say. While a horsepower, pre-smog or post, remains 746 watts (or 736, for metric horsepower), the way that output was measured has changed quite a bit. Let’s explain:

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