Porsche 917

Lore & Background

In an effort to reduce the speeds at Le Mans and other fast circuits of the unlimited capacity Group 6 prototypes (such as the seven-litre Ford GT40 Mk.IV and four-litre V12 Ferrari P) the Commission Sportive Internationale (then the independent competition arm of the FIA) announced that the International Championship of Makes would be run for three-litre Group 6 prototypes for four years from 1968 through 1971. This capacity reduction would also serve to entice manufacturers who were already building three-litre Formula One engines to adapt them for endurance racing.

Well aware that few manufacturers were ready to take up the challenge immediately, the CSI also allowed the participation of five-litre Group 4 sports cars, of which a minimum of 50 units had to be manufactured. This targeted existing cars like the aging Ford GT40 Mk.I and the newer Lola T70 coupé. In April 1968, facing few entrants in races, the CSI announced that the minimum production figure to compete in the sport category of the International Championship of Makes (later the World Sportscar Championship) was reduced from 50 to 25, starting in 1969 through the planned end of the rules in 1971.

Reader's Guide

The car's chassis was designed by Helmuth Bott and the engine was designed by Hans Mezger, both under the leadership of Ferdinand Piëch. The car was built around a very light spaceframe chassis (42 kg) 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 Mezger. A completely new flat-12 block was designed without the cylinder offset needed by a boxer design to keep the engine compact.

The 'Type 912' engine featured a 180° flat-12 cylinder layout with six crank throws (each conrod journal shared by opposing piston pair) as opposed to twelve on a boxer, twin overhead camshafts gear-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 type 920 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. It used many components made of titanium, magnesium and exotic alloys that had been developed for lightweight 'Bergspyder' hill climb racers. Other methods of weight reduction were rather simple, such as making the gear shift knob out of birch wood, some methods were not simple, such as using the tubular frame itself as oil piping to the front oil cooler (a design used successfully by Lotus beginning with Lotus 22 of 1962).

Bodywork made from Fiberglass saved further weight, though at the cost of safety in the event of an accident. This led to automotive writer James May nicknaming the 917 'the world’s fastest canoe.' There are at least eleven variants of the 917. The original version had a removable long tail/medium tail with active rear wing flaps.

These were banned in May 1969 after crashes in Formula 1. As a result the 917 had considerable handling problems at high speed because of significant rear lift. The handling problems were investigated in late 1969 at a joint test at the Österreichring by the factory engineers and their new race team partners JW Automotive.

Did You Know?

• The 917 gave Porsche its first overall win at the 24 Hours of Le Mans in 1970, a feat it repeated in 1971.
• The original 4.5-litre engine produced around 520 bhp in 1969, later enlarged to 5 litres producing 630 bhp.