Before 1970, General Motors had an edict that restricted cubic inches depending on the bodystyle. Chevrolet’s compact (Chevy II/Nova), mid-size (Chevelle), and pony car (Camaro) could not have anything larger than a 396, while full-size cars and the Corvette could get the 427. Meanwhile, across town at Chrysler and Ford, they were running amuck with 7-Liter monsters like the 426 Hemi and Boss 429.
Knowing that credibility was built on the street as much as on the racetrack (which, by the way, was never sanctioned by General Motors due to a racing ban that began in 1963), the folks at Chevrolet created a way to build a few Chevelles and Camaros with 427s. Instead of offering them as Regular Production Orders (RPO), they were built through the Central Office Production Order (COPO) channel. This channel was normally used for fleet orders like for the phone company, so they were equipped to handle things that were not quite regular production. A little over 300 COPO Chevelles and an estimated 1,000 COPO Camaros were built with the L72 427, which was rated at 425 horsepower.