After two years of building Shelby GT350s based on Ford's 289 small block-powered Mustangs, in 1967 Shelby rolled out the big block-powered GT500 as a big brother to the GT350. It was powered by either a Ford 427 or Ford 428, two engines that were similar in size but from different engine families that had different power characteristics.
The Shelbys grew in size for 1969 and '70, when Ford bought the rights to Shelby's products. The GT500 was dormant until 2007, and along the way Ford occassionally applied the name of Shelby's Cobra roadster to hot rod Mustangs, muddying the waters for casual fans who couldn't tell whether a Cobra was a classic two-seat roadster or a Mustang with a big engine.
Since Ford revived the GT500, it has enjoyed continuous improvement to reach the amazing 2020 edition of the car. Ford doesn't build big block V8s anymore, so the newer Shelbys are differentiated from lesser Mustangs by the addition of a supercharger to pump up the power to GT500-worthy levels.
1967 Shelby GT500. Image source: Ford Motor Co.
1968 Shelby GT500. Image source: Mecum Auctions
1968 Shelby GT500 Convertible. Image source: Ford Motor Co.
1969 Shelby GT500. Image souce: Mecum Auctions
1970 Shelby GT500 Convertible. Image source: Mecum Auctions
1978 Ford Mustang II King Cobra was the closest Ford got to offering a performance car that used Shelby nomenclature during the 1974-'78 Mustang II years. Image source: Ford Motor Co.
1979 Ford Mustang Cobra used a turbocharged four-cylinder in place of the traditional V8. Image source: Ford Motor Co.
2007 Ford Mustang Shelby GT500 marked the return of the GT500 name, and with it, a supercharged V8 rated at the 500 horsepower suggested by the car's name. Image source: Ford Motor Co.
2014 Ford Mustang Shelby GT500 saw a power bump to 662 horsepower. Image source: Ford Motor Co.
2020 Ford Mustang Shelby GT500 delivers 760 horsepower in an astonishingly easy to drive package. Image source: Ford Motor Co.