The car was built around a very light spaceframe chassis (42 kg (93 lb)) which was permanently pressurised with gas to detect cracks in the welded structure. Power came from a new 4.5 litre air cooled engine designed by Hans Mezger. The ‘Type 912′ engine featured a 180° V-engine layout, twin overhead camshafts driven from centrally mounted gears and twin spark plugs fed from two distributors. The large horizontally mounted cooling fan was also driven from centrally mounted gears. The longitudinally mounted gearbox was designed to take a set of four or five gears.

To keep the car compact despite the large engine, the driving position was so far forward that the feet of the driver were beyond the front wheel axle.

The car had remarkable technology: Porsche’s first 12-cylinder engine, and many components made of titanium, magnesium and exotic alloys that had been developed for lightweight “Bergspider” hill climb racers. Other methods of weight reduction were rather simple, such as making the gear shift knob out of Balsa wood.

The domination of Gulf-Wyer and Martini Porsches in 1971 was overwhelming. The only potential challenger to the 917 appeared early in the season: Roger Penske had bought a used 512S chassis that was totally dismantled and rebuilt beyond M specification. The car was specially tuned for long races, receiving many unique features among which were a large rear wing and an aviation-inspired quick refueling system. The engine was tuned by Can-Am V8 specialist Traco and able to deliver more than 600 hp (450 kW). Penske’s initiative was not backed by Ferrari works. This 512M, painted in a blue and yellow livery, was sponsored by Sunoco and the Philadelphia Ferrari dealer Kirk F. White. Driven by Penske’s lead driver Mark Donohue, it made the pole position for the 24 Hours of Daytona and finished second despite an accident that required almost an hour in the pits. For the 12 Hours of Sebring the “Sunoco” made the pole but finished the race at the sixth position after making contact with Pedro Rodríguez’s 917. Despite being fastest on track on a few occasions, the 512M was not a serious contender.
The presence of the 512M “Sunoco”, as well as the Alfa Romeo T33/3 which won Brands Hatch, the Targa Florio and Watkins Glen, forced Porsche to pursue their efforts in research and development: tails of the 917K and the 908/3 were modified with vertical fins, and the 917 LH aerodynamics received further improvements. New chassis made of magnesium were developed, even though this material could burn vigorously in the instance of a fire.

A heavily modified car, the 917/20, was built as test-bed for future Can-Am parts and aerodynamic “low-drag” concepts. The 917/20 which had won the test race at Le Mans was painted in pink for the 24 hours race, with names of cuts of meat written in German across it in a similar fashion to a butcher’s carcass diagram, earning it the nickname “Der Truffeljäger von Zuffenhausen” (The Truffelhunter of Zuffenhausen) or just plain “Pink Pig”.

Yet at Le Mans, once again it was not the new machinery that won. The white #22 Martini-entered 917K (chassis number 053) of Helmut Marko and Gijs van Lennep, equipped with a magnesium frame, set an overall distance record that still stands. On the Circuit de la Sarthe, drivers Gijs van Lennep and Helmut Marko set a distance record of 5335.313 km (3,107.7 miles) at an average speed of 220.2 km/h (137.6 mph), a record that still stands today. A long-tail 917 variant (Car #21 [as seen in the Porsche Museum; Stuttgart, Germany]) also set the highest speed ever recorded on the Mulsanne Straight: 384 km/h (240 mph).