PORSCHE 917 kH

Cette collection est une adaptation de Porsche Racing collection - Éditeur : Centauria Editore s.r.l.

The most refined engine never created by porsche

The 907's engine was designed by Hans Mezger, father of the V6 turbo that helped McLaren win the Formula 1 World Championship in 1984, 1985 and 1986. The 917's 'flat' twelve-cylinder engine was the result of the combination of two 2.2-litre 6-cylinder monoblocs from the 911; to limit its length, each pair of opposing pistons attacked the same crankshaft crank, resulting in a 180° V engine.

Porsche's traditional air-cooling system involved a horizontal fan capable of blowing 2,500 litres of air per second. The cylinder heads, one per bank, were made of light aluminium alloy. The crankcase was made from a magnesium alloy, while the connecting rods were made from titanium. The two camshafts per bank activated 2 valves per cylinder, forming an angle of 65° between them, and the mechanical injection system was supplied by Bosch. Each cylinder also accommodated two spark plugs.

[THE ONE-PIECE CYLINDER HEADS ARE MADE OF ALUMINIUM ALLOY.]

Another original feature was the fact that the power take-off was located in the centre of the crankcase, where the gears that drive the camshafts are also located, along with those that drive an auxiliary shaft and then the clutch. The highly complicated dry sump lubrication system comprised several pumps to ensure optimal oil circulation.

POWER, LIGHT WEIGHT AND AERODYNAMICS

At the time, Porsche already had a great deal of experience in lightweight materials, and the 917 used a chassis made from aluminium tubes (magnesium in 1971), with a body constructed from fibreglass and synthetic resin, reinforced around the door openings with aluminium tubes.

To optimise performance on different circuits, two aerodynamic configurations were examined.

The short-tail configuration (KH) was better suited to winding tracks because it generated more downforce; it was completed by two vertical fins in 1971. On the other hand, the long-tail configuration with horizontal wing (LH) enabled higher top speeds to be achieved, to the extent that a 917 equipped in this way came close to 400 km/h on the Hunaudières straight, a stretch more than 6 km long, at Le Mans.

[AT LE MANS, ON THE HUNAUDIÈRES, APPROACHING 400 KM/H].

As for the transmission, Porsche opted for a four- or five-speed gearbox, depending on the circuit, while the suspension was based on the classic layout of two oscillating superimposed wishbones combined with Bilstein shock absorbers and coil springs. The four disc brakes were dual-circuit to minimise the risk of failure.

The car in which Elford and Larrousse won the 1971 12 Hours of Sebring is on display at the Porsche Museum in Stuttgart.

UP TO 1,500 BHP FOR AMERICA

The original version of the engine, with a displacement of 4,494 cm3, initially produced 520 bhp at 8,000 rpm, a figure that quickly rose to 580 bhp at 8,300 rpm. In 1970, the royal year of the 917, displacement was increased to 4,900 cm 3 and power peaked at 600 bhp, then 630 bhp following the adoption of Nikasil-coated cylinders. The engines destined for the North American CanAm championship, where regulations imposed very few restrictions, were equipped with 2 turbochargers, with the result that the latest version in 1973, increased to 5,374 cm 3, offered a staggering power output: from,100 to 1,200 bhp for the race settings and up to 1,500 for qualifying practice.

Engineers Valentin Schäffer, left, and Gerhard Küchle, right, played a major role in the development of the 917's 12-cylinder engine, which remains the only Porsche engine with such a fractional displacement. © IXO Collections SAS - Tous droits réservés.

At the start of its sporting career, the 917 was as fast as it was difficult to push it to its limits, so much so that some drivers preferred to give up Porsche's new 'weapon' to race the more docile 908. © IXO Collections SAS - Tous droits réservés.

In 1974, Count Gregorio Rossi de Montelera, owner of Martini & Rossi, had a 917 converted by Porsche for street use, but he was unable to get it homologated in Europe. © IXO Collections SAS - Tous droits réservés.

A touch of luxury is added by the balsa wood gearstick knob. This particular feature will be used as a quote on the magnificent Porsche Carrera GT of 2003. © IXO Collections SAS - Tous droits réservés.

THE 917: A HOLLYWOOD STAR

The 917 KH played an important role in the 1971 film Les 24 Heures du Mans, starring Steve McQueen. The film was not a great success on its release, but is considered by enthusiasts to be one of the most realistic racing films ever produced. In the film, the car that was used was a 917 No. 20 entered in the 1970 Le Mans 24 Hours by the Gulf team with Jo Siffert-Brian Redman, failing to finish the race, which was won by the sister car of the Porsche-Salzburg team of Hans Hermann-Richard Atwood.

The race scenes were filmed from a Porsche 908, normally used for the race. Steve McQueen, a very good amateur driver, wanted to take part in the race, but the film's production insurance company refused, as they considered the risks too great. A 917 KH used in the film was sold at auction in 2017 by Gooding & Company for over $14 million.