In 1975 , Cosworth developed the DFX engine . A turbocharged 2.65 litre engine , the DFX became the standard engine to run in IndyCar racing . In 1975 ; Cosworth developed the DFX , by destroking the engine to 2650 c and adding a turbocharger , the DFX became the standard engine to run in IndyCar racing , ending the reign of the Offenhauser , and maintaining that position until the late 1980s .