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The True HP of the 10 Most Powerful Classic Era Muscle Cars

No longer rumor, it’s been established that 60s Muscle Car HP was under-rated. We explain how and why and how much horsepower these motors actually produced.

There have been two reasons given for the motivation of the factory to under-report the horsepower of their muscle cars: insurance and NHRA classifications.

Certainly insurers were getting nervous when they started to see cars being introduced, starting with the Pontiac Tempest GTO, with high horsepower in a relatively small car. And as all insurance is based on risk, the insurance companies apportioned higher premiums on these big horsepower cars. To what degree the insurance companies saw through this rouse is unknown. The under-rating rumors were all over the car magazines at the time, and insurance companies aren’t dumb, so in the end it may not have made much difference.

The other reason is much more tangible. The NHRA placed new cars into Stock categories based on weight and stated horsepower. And in the 1960s, drag racing was as important to car sales as NASCAR is today. At that time, Indy was a one-time a year event, ther other events not receiving much coverage, and NASCAR was a regional series in the Southeastern US. Drag racing was where it was at – just a quick survey of music (409, Little Deuce Coupe, Little Old Lady from Pasadena, etc.) and TV shows – Grandpa Munster had a dragster and a drag-style custom car even appeared on Star Trek. As just a wild guess, it was probably 75% NHRA, 25% insurance as motivation for under-rating an engine.

So did the carmakers just lie? Not, probably not. One of the easiest ways to underrate an engine is to specific a maximum RPM below peak horsepower. As you’ll see in the analysis below, several of the most powerful engines had horsepower ratings published¬† at an engine speed below maximum.

The other way to do was was via the testing process itself. If you’re not familiar with the old style of Gross engine power ratings, the engines were measured on a dynamometer in what could be described as full-race trim. Intake air temperature, density, and volume were all controlled to provide maximum power, no restrictive air cleaner was required, carburetor and ignition were adjusted with watchmaker precision, and an open exhaust was used. Not really a good replication of the conditions in which the consumer will drive, which brought about the change to NET ratings in the early 1970s.

So, if you want to have your engine produce less horsepower than its capable of, you need only adjust one or two of the variables mentioned about and there’s an instant drop of horsepower.

That said, we’re relying here on the excellent research of author and automotive historian Roger Huntington who researched these classic muscle engines to determine, scientifically rather than hearsay and rumor, as to whether these monster motors were underrated, and if so by how much. By taking samples from many different areas – dyno tests of exact rebuilds of classic motors, drag race results, 0-60 times, and other test results and developed an algorithm by which he could compare claims to reality. For all his hard work, we thank him (and if you’re interested in this stuff, check out his books).

Soc click Next to view the top 10 horsepower makers from the Classic Muscle Car era:

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Categories: Gear Grinding

Chris Riley
About Chris Riley

I have been wrecking cars for as long as I’ve been driving them but I keep coming back for more. Two wheels or four, I’m all in. GearHeads.org gives me a chance to give something back to the automobile community.