The Cosworth DFX engine was built specifically for competing in the U.S. It is a turbocharged version of Cosworth’s DFV engine used in Formula One competition. Cosworth was partnered with Lola chassis and drivers such as Rick Mears, Johnny Rutherford, Al Unser and Bobby Unser. In a fourteen-year span, starting in 1976, the DFX won 10 Indy 500 races.
Some more background:
The DFV engine was originally produced by Cosworth for Formula One motor racing. It was developed in 1967 under Ford sponsorship for Colin Chapman’s Team Lotus.
The DFX, a turbocharged version of the DFV, was developed privately by the Vels Parnelli Jones team for the 1976 USAC season.
Cosworth became involved in the project soon after, and the engine was known thereafter as the DFX. It went on to dominate Indy car racing in much the same way as the DFV had dominated Formula One.