One of the rarest big-block V8 engines from Ford is the Calliope V8, which has a capacity of 427 cu-in. The experimental engine was designed for Ford's ambitions to win at Le Mans with the GT40.
The Boss 302 Mustang Engine Is The Rarest Small Block V8 From Ford In the early 1960s ... A mighty 10-cylinder unit aimed at a new GT40 supercar, but that never saw the green light of production.