For the 1974 season, Porsche produced yet another evolution of the 911. Developed around the 3-litre RS homologation special, the 3-litre RSR became the most successful Group 4 car of its era.
In its early years, the RSR swept all before it in IMSA, Trans Am and the FIA World Championship, production beginning in late 1973.
They were equipped with Typ 911/75 engines featuring high-lift camshafts, Bosch slide injection and twin plug ignition. There was also a large capacity dry sump oil tank and dual megaphone exhaust from the 2.8 RSR.
Displacement remained unchanged from the RS at 2992cc but the compression was upped from 9.8 to 10:3.1, the result having been 330bhp at 8000rpm.
The five-speed transmission from the RS was installed along with a new dry plate Fichtel and Sachs sintered clutch. Coil springs were either steel or titanium.
Visually the 3-litre RSR was enhanced with special five-spoke centre-locking 15-inch wheels, these having been 10.5-inches wide at the front and a massive 14-inches at the back.
Ultra-light grassfire panels were used for the ventilated wheel arch extensions, bumpers, front lid, engine cover and rear spoiler.
Inside, the stripped-out cockpit got a solitary high-backed Recaro bucket seat with vinyl bolsters and cloth center, a six-point racing harness holding the occupant firmly in place.
Weighing in at a mere 900kg, the RSR was obviously a very quick car, in excess of 170 mph having been possible while 0-60 took less than five seconds.
Towards the end of 1974, most cars were coming out of the factory with closer to 350bhp, the last dozen examples (made from mid 1974) having been built on the 1975 model year H-series platform.
Consequently, these cars use a 560 as opposed to a 460 VIN prefix. Some later cars were also equipped with the Carrera Turbo-style flat front bumper.
The RSR raced through the 1974 and 1975 seasons vanquishing the opposition and providing Porsche with its most successful customer racing car.
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