In the late 1960s, the Commission Sportive Internationale was concerned that speeds of Group 6 prototype sports cars were becoming too high. It therefore decreed that from 1968, the International Championship for Makes would be restricted to three litres. However, to allow for makes which would not have cars ready in time, it permitted Group 4 sports cars of up to five litres.

This directive from the CSI inadvertently gave rise to the building of one of the greatest and most dramatic racing cars ever — the mighty Porsche 917.

The new Porsche first appeared in 1969, and unlike the Ford GT40 of that period it was not built with a central monocoque tub, but in the older but well-tried system of a very light spaceframe chassis similar to that of the Porsche 908. Weighing just 42kg, the chassis tubes contained pressurised gas, a pressure gauge enabling any cracks to be easily detected. Low weight was paramount: the glass-fibre body was very thin and even the gear knob was made of balsa wood.