The Ford GT40 was a high performance sports car and winner of the 24 hours of Le Mans four times in a row, from 1966 to 1969 (in 1967 with a different body, though). It was built to win long-distance sports car races against Ferrari (who won at Le Mans six times in a row from 1960 to 1965). That car used the Gurney Weslake engine with the special alloy heads made by Weslake.
The car was named the GT (for Grand Touring) with the 40 representing its overall height of 40 inches (1.02 m, measured at the windshield) as required by the rules. Large displacement Ford V8 engines (4.7 L and 7 L) were used, compared with the Ferrari V12 which displaced 3.0 L or 4.0 L.
Early cars were simply named "Ford GT". The name "GT40" was the name of Ford's project to prepare the cars for the international endurance racing circuit, and the quest to win the 24 Hours of Le Mans. The first 12 "prototype" vehicles carried serial numbers GT-101 through GT-112. The "production" began and the subsequent cars, the MkI, MkIIs, MkIIIs, and MkIVs, numbered GT40P/1000 through GT40P/1145, were officially "GT40s". The name of Ford's project, and the serial numbers dispel the story that "GT40" was "only a nickname."
In an effort to develop a car with better aerodynamics and lighter weight, it was decided to retain the 7 liter engine, but redesign the rest of the car. In order to bring the car more "in house" and lessening partnership with English firms, Ford Advanced Vehicles was sold to John Wyer and the new car was designed by Ford's studios and produced by Ford's subsidiary Kar Kraft under Ed Hull. There was also a partnership with the Brunswick Aircraft Corporation for expertise on the novel use of honeycomb aluminium panels bonded together to form a lightweight but rigid "tub". The car would make full use of the new and more liberal Appendix J regulations for race car construction, and was therefore known as the J-car.