the 1971 Interserie championship. 1971 917/10: The 917/10 was built for Can-Am racing, with a 5 litre engine, new bodywork and weight pared to a minimum. It was run in the latter part of the 1971 Can-Am season by Jo Siffert, with moderately successful results. 1971 917/20: The 917/20 was a one-off experimental R&D car. It was made as an intermediate car to combine the low drag of the Langheck and the stability of the Kurz, and was also a test-bed for future Can-Am parts and aerodynamic low-drag concepts. It was only raced once, at the 1971 24 Hours of Le Mans where it was entered by the Martini International team and driven by Reinhold Joest and Willi Kauhsen. Known as the "Pink Pig" for its broad proportions, it was given a pink livery with names of meat cuts running over the bodywork. Although it qualified seventh and ran as high as third, it retired from the race after an accident caused by brake failure at Arnage while Joest was driving. 1972 917/10: The revised 917/10 was Porsche's first full-scale attempt at Can-Am for 1972. This car ran the 5.0 litre flat-12 and was modified to accommodate additional compression; two turbochargers were added to give the car tremendous horsepower. George Follmer won the championship in the Roger Penske car. 1973 917/30: The 917/30, the final official iteration of the 917, is one of the most powerful sports racing cars to have ever existed. The car had all new bodywork, and the twin turbocharged engine was bored out to 5.4 litres giving it 1100–1580 horsepower, depending on the state of tune. These cars dominated Can-Am racing to such an extent that the series lost popularity in the United States. A total of six chassis were built. Racing history 1969-1971 World Sportscar Championship 1969 In testing, it soon appeared that the Porsche 917 did not work well on the race track. Porsche factory driver Brian Redman recalled that "it was incredibly unstable, using all the road at speed." Many thought that the 4.5-litre engine was too much for the frame. The suspension and the stability of the frame were suspected, but modifications did not improve the problem. It was finally determined that the "long tail" body was generating significant lift on the straights, as the 917 was faster than anything previously built for Le Mans . As with former under-powered Porsches, the