The 1974-75 Porsche 911 Carrera RSR was the race-ready variant of the Carrera 3.0 RS, which continued as a privateer race car only, featuring a new 3.0-liter engine, the Type 911/75, capable of 330 hp. While roughly 54 cars were built in RS trim, an additional 55 examples were completed in RSR trim - dedicated lightweight racing cars intended strictly for competition. 15 of of those samples were reportedly built for the International Race of Champions series, or IROC, created by Roger Penske, Les Richter, and Mike Phelps.