The Porsche 917 initiated Porsche winning performances at 24 Hours of Le Mans in 1970 and 1971. The car resulted from a change in endurance homologation rules announced in 1968. The new contender class would have engines up to 5 liters and a minimum of 25 produced units was required. The 917 engine was flat 12 with 4,5 liter because for faster development it was built from extension of 3 liter flat 8 of the Porsche 908. The chassis was also developped starting from the 908. The Porsche 917 with closed composite body was first shown at Geneva Motor Show in 1969.