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The long road to LeMans
After Porsche burst onto the racing scene in the early 1950s, the German company had slowly, but gradually progressed through the sportscar racing classes with one goal in mind: an overall victory at LeMans. Porsche's first success at the legendary 24 Hours race came in 1952, when a 356 took the victory in the 751 - 1100 cc class. Patiently Porsche developed new racing cars like the 550, which still used many parts from the road going Porsche 356. By the mid-1960s the gap between road and racing cars grew bigger and bigger, and with it the racing successes increased as well.
Ford and Ferrari were fighting for the LeMans victory with very advanced and powerful cars in the mid-1960s. The cars fielded by Porsche were equipped with engines displacing only a fraction of those found in the leading cars. This however did make them more nimble and competitive on tight and curvy tracks. Unfortunately the LeMans track consisted of long straights, best suited to the most powerful of cars. A rule change at the end of the 1967 season seemed to bring Porsche's new three litre racer, the 908 into contention. The old prototype class was abandoned in favour of a limited production 5-litre Sportscar class (Group 4) and a 3-litre Prototype class (Group 6).
Only two cars were built in sufficient numbers (50) to be homologated for Group 4; the Lola T70 and Ford GT40 Mk I. Both cars were powered by 400+ bhp engines, which was too much for the new 908 to compete with on LeMans. A JWA / Gulf entered GT40 took the LeMans win, but chased by two Porsches, victory was closer than ever! A number of manufacturers appealed the new regulations stating that a 50-car production run in one year was too much for a racing car. For 1969 the number was decreased to 25, which opened the door for a number of manufacturers to at least consider designing and building a car to take on the Lolas and Fords.
Decision making time
Under the leadership of Ferdinand Piech, the Porsche racing department had produced a new car almost every year in the mid-1960s. All of them were prototype racers, yet the production reached the now magic figure of 25 almost always, with many cars sold to privateers. Piech figured that if they would build a Group 4 racer, much of the money invested could be earned back from sales to privateers. One of the biggest problems was the enormous and new engine the car would need, especially considering the fact that Porsche's largest engine at the time displaced just under three litres. With little time for testing available, the fact that 25 cars had to be produced before the car could be raced was also a big concern, so the design had to be right straight away.
With less than ten months to go before the 1969 24 Hours of LeMans race, Porsche set out to design the new car, which represented the single biggest step in their racing history. Porsche's strategy of gradual development had served them very well in the past, but Piech understood more was needed now to finally clinch the overall victory. According to very strong rumours Volkswagen funded approximately 2/3s of the costs of the racing program under the sole condition that Porsche would maintain the use of air-cooled engines for their competition cars. A very interesting way of promoting the air-cooled engine, which Volkswagen used in all of their cars of the day.
The birth of a legend
Weight saving was on the top of the list of the designers and all experience Porsche had gathered on exotic materials was used on the '917' as the new car was to be known. Although the tubular frame was almost identical to that of the 908, it was now constructed of aluminium instead of the steel used on the 8-cylinder racer. The chassis lost some of its rigidity compared to the steel one, but its extremely low weight of just 46 kg more than made up for that. Like all racers of the day, the 917 was suspended all-round by fully independent suspension, made up of wishbones. More exotic materials were found here, with the coil springs used being made up of titanium.
The heart of the 917 was its new engine. The engine used identical cylinders to those found on the 908, just four more, giving a twelve cylinder engine displacing just under 4.5 litres. Two things set the new '912' engine apart from the older engines: the design of the crankshaft and of the camshafts. Whereas the 908 used a boxer type crankshaft, the 912 engine was fitted with a crankshaft similar to those found in 'V'-engines, resulting in a relatively shorter engine. The double overhead camshafts were driven from centrally mounted gears, which effectively cut the engine in two six cylinder sections. A long tradition of shaft driven camshafts was abandoned.
Although the flat-12 was relatively short, it was still a huge engine. In order to stick with the 908's wheelbase, the cockpit was moved forward, giving a somewhat akward driving position. A slightly wider body was fitted compared to the 908, to clear the larger engine and wider track. The rear body featured a detachable tail section, which enabled the customer to choose between a high-downforce or a low-drag tail to suit the needs of the track. The rear wing was fitted with movable flaps, similar to the system used on the longtail 908 coupes. Cold air was blown to the engine by a big fan fitted on top of the flat-12.
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