Cosworth needed to replace the DFS engines used in IndyCar and Champ Car racing. Cosworth designed the X-series, beginning in 1992 with the XB. The XF was built for the 2000 season to replace the XD. It was picked as the spec engine for the Champ Car World Series in 2003. The most recent version is the 2.65 litre XFE, used through 2007. The Champ Car World Series set a rev limit of 12,000 rpm. The 2004 model of the XFE was rated at 750 horsepower for normal running. It could produce 800 horsepower during the "Push-to-Pass" mode.