Ken Wallis had developed a workable concept for harnessing a gas turbine to a race car and initially pitched the idea to Dan Gurney and then Carroll Shelby, both of whom declined. Andy Granatelli of STP expressed interest, and Wallis's crew moved into STP's Paxton division facility in Santa Monica to begin construction in January 1966. A badly warped aluminum frame during heat treatment eliminated any possibility of the car racing in 1966, but a rebuilt machine was ready for 1967.
The car was built around an aluminum box-shaped backbone, with the driver seated on the right side and the engine mounted on the left. That engine was a Pratt and Whitney Canada ST6B-62 turbine, a small aircraft powerplant that, while never successful as an automobile engine, would go on to become one of the most popular turboprop engines in aviation history. Power was transmitted through a Ferguson four-wheel-drive system; a torque converter eliminated any need for a clutch or gearshift, meaning the driver needed only to ease off the brake pedal to get the car moving. A movable panel mounted behind the cockpit served as an airbrake. The suspension A-frames had airfoil cross-sections and the coil springs were located inside the backbone. The car weighed 1,750 pounds against an Indy minimum of 1,350 pounds.
USAC had limited the engine intake area to 23.999 square inches to cap the turbine's power output, but the engine still produced around 550 horsepower. Drivers reported a characteristic three-second throttle lag, a feature that distinguished the car's driving feel from any conventional piston-engined competitor.
Parnelli Jones drove the car during pre-race tire testing in Phoenix and came away impressed. He agreed to pilot it at Indianapolis after being offered a substantial cash fee and a share of any prize money. Jones qualified the car in sixth place at 166.075 mph.
From the start of the race, Jones dominated. He took the lead quickly and rarely relinquished it, running away from the field in near-silence compared to the exhaust roar of the piston-engined cars around him. With only eight miles remaining — effectively just three laps on the 2.5-mile oval — Jones coasted into the pits as a transmission bearing failed. The race was won by A.J. Foyt.
The defeat became one of the most discussed near-misses in Indianapolis history. Jones and Granatelli had come close enough that the sport's governing body moved swiftly to ensure it would not happen again.
Within a month of the 1967 race, USAC cut the allowable turbine air intake area from 23.999 to 15.999 square inches and imposed the ruling immediately, bypassing the customary two-year notice period given for major engine changes. With the reduced inlet area, the maximum achievable lap speed dropped to approximately 161 mph, making the turbine cars significantly less competitive.
The refurbished car was entered by STP in the 1968 Indianapolis 500 with Joe Leonard driving, but it crashed into the turn four wall during practice and never raced again. That same year, Andy Granatelli also backed the Lotus 56 program, which used a modified version of the same ST6B-62 engine in a more advanced wedge-shaped body. Three Lotus 56s were entered and all retired; Mike Spence was killed testing one of them before the race. USAC subsequently banned turbine engines and four-wheel drive entirely.
Ken Wallis also went on to design a similar car for Carroll Shelby, who entered two turbine cars for the 1968 race intending Denny Hulme and Bruce McLaren as drivers. Both were withdrawn following Spence's death, officially on safety grounds, though the new intake restrictions had also effectively neutralized their competitiveness.
The original Turbocar was donated to the Smithsonian Institution's National Museum of American History by the STP Corporation. The car displayed at the Indianapolis Motor Speedway Hall of Fame Museum is an exact replica built from original blueprints. The cowling for the car was misplaced for over two decades and was found in 2007 in a Smithsonian office.
The STP-Paxton Turbocar remains the defining example of how a radical technology could expose the limits of existing regulations in a single race weekend. Its near-victory prompted the fastest major rules revision in Indianapolis 500 history, and the story of Parnelli Jones coasting to a stop with the finish line in sight became central to the lore of the event. The concept directly inspired both the Lotus 56 and Shelby's own turbine program, making 1967 and 1968 the peak and the end of the turbine era at Indianapolis in the same breath.