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The 917 Kurzheck Coupé (917K) first appeared in 1970 and contributed more to the Porsche 917 story than any other variant. It was a high-down force version that featured a cut-off tail for increased downforce. This reduced the cars top speed, as much as 30 mph. Le Mans winner 1970, Interserie winner 1970 and Manufacturers' World Championship for Porsche in 1970.
The “shark fins” on the tail gave the Porsche 917 KH 1971 greater directional stability and reduced wind resistance by 11 percent. In 1971 a veritable armada of six Porsche 917s started at Le Mans. The car with start number 22 was special. The white race car with the characteristic Martini stripes had the new “shark fins” on the tail that Porsche had first used in pretraining in April. This 917 was also the first Porsche with a magnesium tubular frame to be used in a race.
The Group 7 class in CanAm was virtually unlimited with regard to regulation, so Porsche was free to try many different avenues to source extra power. Two main themes were explored: the first was to go into uncharted territory and turbocharge engines with an exhaust-driven turbine. Eventually this was the chosen route, but it didn't reach fruition until a larger 16-cylinder engine was tried.