At its prime, the Chevelle SS had 450 horsepower and could run the quarter mile in the low 12 second range. Then the gas crisis hit and the muscle car era was over.
We've already covered pony cars in an earlier series, and the line between pony cars and muscle cars is not the clearest one. But even if it is sometimes difficult to see these days, American automakers genuinely did used to try to make a distinction between pony cars and muscle cars. Muscle cars were usually bigger and more expensive, and weren't quite so deliberately aimed at young people.
The distinction is easiest to make when talking about a car made by a manufacturer which also had a pony car in the lineup, and thus the Chevrolet Chevelle SS is a good starting point. Another big difference between muscle and pony cars is that a pony car is still considered a pony car even in its base trim, whereas muscle cars are usually based on mainstream models and are only considered muscle cars when in performance trim. Thus we have the Chevelle SS, based on one of Chevy's most successful nameplates in history, yet certainly distinct from the station wagons which also wore the Chevelle badge.
The Chevelle was first introduced in 1964, and a Super Sport package was available right from the start. Confusingly, the top trim level of the Chevelle was known as the Malibu, a nameplate which would eventually evolve to replace the Chevelle entirely. The SS package was only available for Malibu models, and SS models would be badged "Malibu SS" for the first couple years of production. The Malibu name would still be applied internally, but the badge on the car disappeared after 1965. This was just one of many changes which happened very rapidly to the SS as the muscle car segment took off like a shot in the mid-sixties.
But Chevelle SS sales never faltered, actually increasing to 86,000 in 1969. The big game changer came in 1970, when Chevy started offering the 454cu-in V8. This was available in two states of tune, one producing 360 horsepower and one producing 450 horsepower (at least, that's the official figure, third-party dyno tests have shown it to be about 470 horsepower). These 454-equipped cars could run the quarter mile in the very low twelves completely stock, and represent the pinnacle of Chevelle SS performance. A less-sporty body style debuted in 1973, and SS sales dropped right off, causing Chevy to drop the option at the end of the model year.
The era of the muscle car was ending anyway, and even if sales had kept up, the SS wouldn't have lasted much longer. The Camaro might be the better-remembered car of the era, not to mention the nameplate which has survived, but the muscle car genre would not have been the same without the Chevelle SS.