By 1953, General Motors' research team had produced the Firebird XP-21, later referred to as the Firebird I, which was essentially a jet airplane on wheels. It was the first gas turbine powered car tested in the United States. The design is entirely impractical, with a bubble topped canopy over a single seat cockpit, a bullet shaped fuselage made entirely of fiberglass, short wings, and a vertical tail fin. It has a 370 hp (280 kW) Whirlfire Turbo Power gas turbine engine, which has two speeds, and expels jet exhaust at some 1,250 °F (677 °C). The entire weight of the car is 2,500 lb (1,134 kg) and had a 100 inch wheelbase.

At first, Conklin was the only person qualified to drive it, and he tested it up to 100 mph (160 km/h), but upon shifting into second gear the tires lost traction under the extreme engine torque and he immediately slowed down for fear of crashing. The car was later test driven at the Indianapolis Speedway by race car driver Maury Rose. The car was never actually intended to test the power or speed potential of the gas turbine, but merely the practical feasibility of its use. The braking system differs from standard drum systems, in that the drums are on the outside of the wheels to facilitate fast cooling, and the wings actually have aircraft style flaps for slowing from high speed.

A miniature version of the Firebird I crowns the Harley J. Earl Trophy, given to the winner of the Daytona 500.