The DFV, an internally combusted 3.0-litre 90-degree V8, had been the dominant Formula One engine since its debut in 1967, designed by Keith Duckworth of Cosworth Engineering with Ford backing. Variants of the engine found use across multiple racing categories over the following decade, including sports car racing and Formula 3000. The North American adaptation, however, arose not from Cosworth's own initiative but from the efforts of an IndyCar team.
The Vels Parnelli Jones team developed a turbocharged, reduced-displacement version of the DFV for the 1976 USAC IndyCar season, doing so against the expressed objections of Cosworth founder Keith Duckworth. Reducing displacement to 2.65 litres and fitting a turbocharger allowed the engine to comply with Indy car equivalency regulations while producing substantially more power than a naturally aspirated unit. The Parnelli-Cosworth car scored its first victory at the 1976 Pocono 500, with Al Unser driving. Unser took two further wins that season in Wisconsin and Phoenix, finishing fourth in the championship.
Duckworth had attended the Pocono victory as a guest of Parnelli Jones and Vel Miletich, who sought to position the Vels Parnelli team as North American distributor for the turbocharged engine. However, Cosworth moved quickly to take control of the programme, recruiting two key engineers from the Parnelli team and establishing development and marketing facilities in Torrance, California. From that point the engine became officially known as the DFX — the "X" designating the North American, turbocharged specification.
The engine retained the fundamental 90-degree V8 architecture of the DFV but was comprehensively reworked for forced induction and the demands of oval racing, where sustained high speeds and fuel economy played a larger role than in the stop-start circuits of Formula One. By the time the DFX reached its competitive peak it was producing over 840 bhp.
The DFX's record in American open-wheel racing is among the most dominant engine performances in motorsport history. It won the Indianapolis 500 in ten consecutive years, from 1978 through 1987, with drivers including Al Unser, Rick Mears, Johnny Rutherford, Bobby Unser, Gordon Johncock, Tom Sneva, Danny Sullivan, and Bobby Rahal. Mears won the race in both 1979 and 1984, and Al Unser took the 1978 and 1987 editions.
In the USAC championship the DFX powered Tom Sneva to titles in 1977 and 1978, with A. J. Foyt adding a third in 1979. The CART series, which superseded USAC as the premier American open-wheel championship, saw DFX-powered cars claim nine consecutive titles between 1979 and 1987, with Rick Mears winning four (1979, 1981, 1982, 1983), Al Unser two (1983, 1985), Johnny Rutherford one (1980), Mario Andretti one (1984), and Bobby Rahal two (1986, 1987).
The engine powered 81 consecutive Indy car victories from 1981 to 1986 and accumulated 153 victories in total across its competitive life. In a brief period during the early 1980s, some DFX engines were badged as Ford units, echoing the Ford branding that had accompanied the original DFV in Formula One.
The DFX's dominance began to be challenged when General Motors financed the British firm Ilmor to develop a competitor for American Indy car racing in 1986. Mario Illien's resulting Ilmor-Chevrolet Indy V-8, which drew on design principles from Cosworth's own DFY Formula One variant of the DFV, quickly took over at the front of the field. Ford responded by commissioning Cosworth to develop an updated version of the Indy car engine.
In 1989 Cosworth introduced the DFS — with the "S" standing for short stroke — incorporating several improvements derived from the Formula One DFR programme, including Nikasil aluminium cylinder liners. The DFS was fielded initially by the Kraco Racing team (Bobby Rahal) and Dick Simon Racing (Arie Luyendyk). Rahal won one race with the engine, at the Meadowlands in 1989, but the programme struggled to recapture the DFX's former supremacy. The Kraco team merged with Galles at the end of the 1989 season and switched to Chevrolet power. Factory development continued into 1990 and 1991 with Scott Brayton and Dominic Dobson, but no further victories were recorded, and the DFS was retired following the introduction of the Ford Cosworth XB.
The Cosworth DFX holds a unique place in motor racing history as one of relatively few engines to have achieved dominance in two entirely different forms of racing, the DFV in Formula One and the DFX on the American oval scene. The transition from team-developed adaptation to factory product, and from challenger to near-monopolist, mirrored the DFV's own trajectory in European racing a decade earlier. The ten consecutive Indianapolis 500 victories from 1978 to 1987 remain a benchmark for engine reliability and performance in the most demanding single event in North American motorsport.