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This is the Peter Gregg car (chassis #930 770 0952) as shown at the Porsche Rennsport 2015. In early 1977, the Peter Gregg car sent home from the Atlanta IMSA race due to ‘illegal modifications.’ This photo shows the car restored with 935 fenders as it was run later in 1977

Sports car racing changed drastically in the early- to mid-1970s. The rules for the World Championship shifted away from the 5-litre cars such as the 917 and Ferrari 512, to the 3-litre versions such as the Ferrari 312PB, Porsche 908 and Alfa Romeo T33 in 1972. While most Porsche customers ran the RSR in GT racing, a few also ran 908s, but Porsche knew the 908 was not competitive for overall victory anymore. It was under powered and with the raising of the minimum weight, it basically lost any advantage it had against the Ferrari and Alfa.

Ludwig Heimrath car (chassis #930 770 0958) restored with 935 fenders, on the grid at Monterey Historics 2016

Porsche started working on the adaptation of their turbo technology (taken from the 917 Can-Am cars) to their 911-based production cars, which saw the introduction of the Martini RSR turbo cars. These ran effectively in 1974 and 1975 as prototype class cars, but still were not quick enough to win overall against the 3-litre cars. Porsche knew that the World Manufacturers Championship in 1976 would switch to production based cars in Groups 4 and 5. They therefore spent 1974 and 1975 developing the Carrera RSR turbo to prepare for the introduction of the 934 and 935 in 1976. Group 4 required a minimum 400 cars to be built, but Group 5 had no minimum number, and allowed more modifications to the production base model.

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