In an effort to reduce the speeds generated at Le Mans and other fast circuits of the day by the unlimited capacity Group 6 prototypes (such as the 7-litre Ford GT40 Mk.IV and 4-litre V12 Ferrari P) the Commission Sportive Internationale (then the independent competition arm of the FIA) announced that the International Championship of Makes would be run for 3-litre Group 6 prototypes for four years from 1968 through 1971. This capacity reduction would also serve to entice manufacturers who were already building 3-litre Formula One engines into endurance racing.
Well aware that few manufacturers were ready to take up the challenge immediately, the CSI also allowed the participation of 5-litre Group 4 Sports Cars, of which a minimum of 50 units had to be manufactured. This targeted existing cars like the aging Ford GT40 Mk.I and the newer Lola T70 coupe.
In April 1968, facing few entrants in races, the CSI announced that the minimal production figure to compete in the Sport category of the International Championship of Makes (later the World Sportscar Championship) would be reduced from 50 to 25, starting in 1969 through the planned end of the rules in 1971. With Ferrari absent in 1968, mainly Porsche 908 and Ford P68 were entered there, with the Ford being a total failure. As a result, old 2.2-litre Porsche 907 often won that category, with John Wyer's 4.7-litre Ford GT40 Mk.I taking wins at faster tracks.
Starting in July 1968, Porsche made a surprising and very expensive effort to take advantage of this rule. As they were rebuilding race cars with new chassis every race or two anyway, selling the used cars to customers, they decided to conceive, design and build 25 versions of a whole new car with 4.5-litre for the Sport category with one underlying goal: to win its first overall victory in the 24 Hours of Le Mans on May 14, 1970. In only ten months the Porsche 917 was developed, based on the Porsche 908.
The 917 proved to be a difficult animal, fast and hard to control the car was unsuccessful until the last race of 1969 when Jo Siffert and Kurt Ahrens drove this car to victory in the 1000km of Zeltweg. For 1970 Porsche would heavily revise the 917, completely dominating the World Championship for Makes.
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