When Dr Ferdinand Piech’s Porsche 917 first turned a wheel in anger, the world of sports car racing was never quite the same. Circuits like Spa, Sebring, Daytona, the Nurburgring and of course, Le Mans, cemented the all-conquering 917 as as one of the greatest Porsche racing cars ever. When the 917 was prepped for competition in the “no holds …