Carroll Shelby fitted the original AC Cobras with the Ford 260 cu.in. V8. After the first 75 cars were
produced the engine was upgraded to the Ford 289 cu.in. In early 1964 Shelby fit a 390 cu.in Ford V8 into a racing Cobra in order to be more competitive against the Ferrari 250GTO and the Grand Sport Corvette, but lack of development hindered the car. Shelby, with the assistance of Ford, then upgraded the Cobra to the 427 cu.in. V8. The 427 sported a larger grill opening, larger tube frame chassis, coil spring suspension all around, and wider fenders. The 427 produced 425 HP in the street version.