In 1973 Porsche introduced the 911 Carrera RSR to compete in the World Sports Car Championship. It used the 911 production car as a base. For homologation purposes, the road going 911 Carrera RS 2.7 was also created. Porsche wanted the new GT car to be campaigned by privateers, but eight pre-production prototypes were also raced in select rounds of the World Championship by the works drivers. In addition to the works team, customers like Brumos and Penske racing teams were also entrusted with these cars. The early RSR competition cars featured a 2.8 litre version of the regular production 911 engine. The flat six was developed for competition use and featured twin-spark ignition, larger intake and exhaust ports, more aggressive camshafts and Bosch fuel injection. This air-cooled engine produced an impressive 308 bhp. The debut was at the ’73 24 Hours of Daytona, where drivers Peter Gregg and Hurley Haywood of the Brumos team took overall victory. The car proved to be extremely successful and also won in the same year the Targa Florio and the 12 Hours of Sebring. The RSR is one of the rarest and most valuable competition Porsches in the collectors car market.