Porsche began experimenting with turbocharging technology on their race cars during the late 1960s, and in 1972 began development on a turbocharged version of the 911. Porsche originally needed to produce the car in order to comply with homologation regulations and had intended on marketing it as a street legal race vehicle like the 1973 Carrera 2.7 RS. The FIA's Appendix “J” rules that brought about the 911 Turbo Carrera RSR 2.1 in 1974 changed in 1975 and 1976.
Porsche 911 turbo evolution
Porsche made its first and most significant changes to the 930 for 1978, enlarging the engine to 3.3 litres and adding an air-to-air intercooler. By cooling the pressurized air charge, the intercooler helped increase power output to 300 hp (DIN); the rear 'whale tail' spoiler was re-profiled and raised slightly to make room for the intercooler. Porsche also upgraded the brakes to units similar to those used on the 917 racecar.
Porsche offered a "Flachbau" ("flatnose" or "slantnose") 930 under the "Sonderwunschprogramm" (special order program) beginning in 1981, an otherwise normal 930 with a 935-style slantnose instead of the normal 911 front end. Each Flachbau unit was handcrafted by remodeling the front fenders. So few were built that the slantnose units often commanded a high premium price, and an initial premium of up to 60 per cent (highly individualized cars even more) over the standard price. 948 units were built. The Flachbau units delivered in Europe usually featured the 330 hp (246 kW) performance kit.