The Chevelle SS represented Chevrolet's entry into the muscle car battle. Early 1964 and 1965 Chevelles had a Malibu SS badge on the rear quarter panel (the sought-after Z16 option had the emblem on the front fender, where 201 Malibu SS 396s were produced); after 1965, the Malibu SS badging disappeared except for those sold in Canada. The Chevelle SS, which became a regular series of its own in 1966 called the SS 396, was the high performance version and had its own line of engines and performance equipment. The performance engines available included 396 in³ V8s - rated at 325, 350 and 375 hp (280 kW) respectively (the mid horsepower 396 was rated at 360 hp (270 kW) for 1966 only and 350 hp (260 kW) thereafter). The SS396 series only lasted three years from 1966 through 1968 before being relegated to an option status just like air conditioning or a radio. The 1966 and 1967 model years also saw the limited run of the 'strut back' 2-dr sport coupe with its own model number, 17, as opposed to model number 37 used on previous and later 2-dr sport coupes.
As with the 300 Deluxe and Malibu in 1969 and only the Malibu from 1970 to 1972, the SS option could be ordered in the El Camino as well.
Source: Wikipedia Chevrolet Chevelle Article.