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The Porsche 917 is a race car that gave Porsche its first overall wins at the 24 Hours of Le Mans in 1970 and 1971. Powered by the Type 912 flat-12 engine of 4.5, 4.9, or 5 litres, the 917/30 Can Am variant was capable of a 0- time of 2.3 seconds, 0– in 5.3 seconds, and a top speed of up to . This is not, however, representative of the majority of 917s. The highest official speed ever clocked for a 917 at Le Mans is 362 km/h or 224.4 mph.〔(Mulsanne's Corner: Maximum Speeds at Le Mans, 1961-1989 )〕 There are at least eleven variants of the 917. The original version had a removable long tail/medium tail with active rear wing flaps, but had considerable handling problems at high speed because of significant rear lift. The handling problems were investigated at a joint test at the Österreichring by the factory engineers and their new race team partners John Wyer Engineering and after exhaustive experimentation by both groups, a shorter, more upswept tail was found to give the car more aerodynamic stability at speed. The changes were quickly adopted into a new version of the 917, called the Kurzheck, or short-tail, with the new version being called the 917K. The 917K, and the special Le Mans long-tail version (called the 917 Langheck, or 917L), dominated the 1970 and 1971 World Sportscar Championships. In 1971, a variant of the 917K appeared with a less upswept tail and vertical fins, and featured the concave rear deck that had proved so effective on the 1970 version of the 917L (see below). The fins kept the clean downforce inducing air on the top of the tail and allowed the angle of the deck to be reduced, reducing the drag in direct proportion. The result was a more attractive looking car that maintained down force for less drag and higher top speed. By this time the original 4.5-litre engine, which had produced around 520 bhp in 1969, had been enlarged through 4.9-litres (600 bhp) to 5-litres and produced a maximum of 630 bhp. The 917K models were generally used for the shorter road courses such as Sebring, Brands Hatch, Monza and Spa-Francorchamps. The big prize for Porsche however, was Le Mans. For the French circuit's long, high speed straights, the factory developed special long tail bodywork that was designed for minimum drag and thus highest maximum speed. On the car's debut in 1969, these long-tail (917L) models proved to be nearly uncontrollable as there was so little down force. In fact, they generated aerodynamic lift at the highest speeds. For 1970, an improved version was raced by the factory (although the John Wyer team still preferred the security of the 917K) and for 1971, after very significant development in the wind tunnel, the definitive 917L was raced by both factory and JW. These cars were so stable that the drivers could take their hands off the steering wheel at speeds which reached 246 mph. In 1971 Jo Siffert raced an open-top 917PA Spyder (normally aspirated) in the 1971 CanAm series. There is also the "Pink Pig" aerodynamic research version (917/20), and the turbocharged 917/10 and 917/30 CanAm Spyders. Porsche 917s also raced in the European Interseries in various configurations. In the 1973 Can-Am series, the turbocharged version Porsche 917/30 developed .〔 The 917 is one of the most iconic sports racing cars of all time, largely for its high speeds and high power outputs, and was made into a movie star by Steve McQueen in his 1971 film ''Le Mans''. 2009 marked the 40th anniversary of the 917, and Porsche held a special celebration at the Goodwood Festival of Speed (3–5 July). ==The birth of the 917== In an effort to reduce the speeds generated at Le Mans and other fast circuits of the day by the unlimited capacity Group 6 prototypes (such as the 7-litre Ford GT40 Mk.IV and 4-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 into 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.〔(Appendix J 1969, Art. 251, Art. 252 ) on (www.fia.com )〕 This targeted existing cars like the aging Ford GT40 Mk.I and the newer Lola T70 coupe. 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) would be reduced from 50 to 25, starting in 1969 through the planned end of the rules in 1971. With Ferrari absent in 1968, mainly Porsche 908 and Ford P68 were entered there, with the Ford being a total failure. As a result, old 2.2-litre Porsche 907 often won that category, with John Wyer's 4.7-litre Ford GT40 Mk.I taking wins at faster tracks. Starting in July 1968, Porsche made a surprising and very expensive effort to take advantage of this rule. As they were rebuilding race cars with new chassis every race or two anyway, selling the used cars to customers, they decided to conceive, design and build 25 versions of a whole new car with 4.5-litre for the Sport category with one underlying goal: to win its first overall victory in the 24 Hours of Le Mans on May 14, 1970. In only ten months the Porsche 917 was developed, based on the Porsche 908. When Porsche was first visited by the CSI inspectors only three cars were completed, while 18 were being assembled and seven additional sets of parts were present. Porsche argued that if they assembled the cars they would then have to take them apart again to prepare the cars for racing. The inspectors refused the homologation and asked to see 25 assembled and working cars. On March 12, 1969, a 917 was displayed at the Geneva Motor Show, painted white with a green nose and a black #917. Brief literature on the car detailed a cash price of DM 140,000, approximately £16,000 at period exchange rates, or the price of about ten Porsche 911s. This price did not cover the costs of development. On April 20 Porsche's head of motorsports Ferdinand Piëch displayed 25 917s parked in front of the Porsche factory to the CSI inspectors. Piëch even offered the opportunity to drive any of the cars, which was declined.〔(Porsche 917 History - 1969 Season (Part 1) ) on (www.porsche917.com.ar )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Porsche 917」の詳細全文を読む スポンサード リンク
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