In an effort to reduce speeds at Le Mans and other fast circuits, the Commission Sportive Internationale announced that the International Championship of Makes would be run for three-litre Group 6 prototypes from 1968 through 1971. The CSI also allowed the participation of five-litre Group 4 sports cars, of which a minimum of 25 units had to be manufactured. In April 1968 the minimum figure was reduced from 50 to 25, starting in 1969. This targeted existing cars like the Ford GT40 Mk.I and the Lola T70 coupé.
Starting in July 1968, Porsche made a surprising and expensive effort to exploit this rule. In only ten months the Porsche 917 was developed, based on the Porsche 908, with one underlying goal: to win Porsche's first overall victory at the 24 Hours of Le Mans on June 14, 1970.
When first visited by CSI inspectors only three cars were completed, with 18 being assembled and seven sets of parts present. Porsche argued that assembling the cars would require taking them apart again to prepare for racing. The inspectors refused homologation and demanded 25 assembled and working cars. On March 12, 1969, a 917 was displayed at the Geneva Motor Show, priced at DM 140,000, approximately £16,000 at period exchange rates — about the price of ten Porsche 911s. On April 20, Porsche's head of motorsports Ferdinand Piëch displayed 25 917s parked in front of the Porsche factory to satisfy the inspectors, even offering them the opportunity to drive any car.
The car's chassis was designed by Helmuth Bott and the engine by Hans Mezger, both under the leadership of Ferdinand Piëch. The chassis was a very light spaceframe weighing 42 kg (93 lb), permanently pressurised with gas to detect cracks in the welded structure. The 'Type 912' engine featured a 180° flat-12 cylinder layout with six crank throws — each conrod journal shared by an opposing piston pair — twin overhead camshafts gear-driven from centrally mounted gears, and twin spark plugs fed from two distributors. The longitudinally mounted Type 920 gearbox accommodated four or five gears.
The driving position was so far forward that the driver's feet extended beyond the front wheel axle. The car used titanium, magnesium, and exotic alloys developed for lightweight hill-climb racers. Weight-reduction methods ranged from simple — a birch wood gear shift knob — to complex, such as using the tubular frame itself as oil piping to the front oil cooler.
At least eleven variants of the 917 were produced. The original version featured a removable long tail with active rear wing flaps, which were banned in May 1969 after crashes in Formula One. The loss of the flaps caused significant rear lift, making the car nearly undriveable at high speed. The solution was found in late 1969 during a joint test at the Österreichring by factory engineers and their new race team partner JW Automotive: comparison with the Can-Am 917PA Spyder showed that its shorter, more upswept tail gave better aerodynamic stability, and these changes were quickly adopted into the wedge-tail 917K — K for Kurzheck, or "short-tail."
By 1971 the original 4.5-litre engine, producing around 520 bhp in 1969, had been enlarged through 4.9 litres (600 bhp) to 5 litres producing a maximum of 630 bhp.
917PA (1969): An open-topped, short-tailed version built for Can-Am racing; only two were built. Jo Siffert drove the second car in the 1969 Can-Am season for Porsche Audi, the North American distributor. Underpowered compared to the dominant McLarens, Siffert's best result was third at Bridgehampton; he finished fourth in the championship.
917K (1970): The definitive short-tail evolution developed after a 3-day test at the Österreichring, where Porsche's chief engineer John Horsman observed a pattern of dead gnats on the car's bodywork — or rather, their absence on the tail — revealing the airflow problem. A new short tail was cobbled together on the spot using aluminium sheets and gaffer tape. The 917K made its debut at the 1970 24 Hours of Daytona and won seven of ten races entered that season.
917L / 917LH (1970–1971): Long-tail, low-drag versions purpose-built for Le Mans. The 1970 917L was 25 mph faster on the straights than the 917K and the Ferrari 512S. The 1971 917LH featured partially enclosed rear wheel covers and a revised suspension; JW Automotive qualified one on pole at Le Mans but none of the three factory long-tail cars finished.
917/20 (1971): A one-off experimental R&D car combining low drag of the Langheck with the stability of the Kurzheck. It was painted pink for Le Mans with names of meat cuts written across it in German, earning the nickname "Pink Pig" or "Der Trüffeljäger von Zuffenhausen." Driven by Reinhold Joest and Willi Kauhsen, it qualified seventh and ran as high as third before retiring with brake failure at Arnage.
917/10 (1972): Porsche's first full-scale Can-Am attempt, running the 5.0-litre flat-12 with twin turbochargers. The turbocharged 850 hp (630 kW) 917/10K entered by Penske Racing won the 1972 Can-Am series with George Follmer, after a testing accident sidelined primary driver Mark Donohue.
917/30 (1973): The final official iteration, one of the most powerful sports racing cars ever built and raced. The twin-turbocharged engine was bored out to 5.4 litres producing 1,100–1,580 bhp depending on state of tune. Six chassis were built. The 917/30 dominated Can-Am to such an extent that the series lost popularity in the United States.
Testing quickly revealed significant instability. Factory driver Brian Redman recalled the car "was incredibly unstable, using all the road at speed." The aerodynamics had been optimised for low drag with the consequence of generating significant lift at high speed. The car's competition debut on May 11, 1969 in the 1000 km Spa saw the Siffert/Redman car clock an unofficial lap time that would have beaten pole, but they chose to use the 908LH long-tail and won. At the 1969 24 Hours of Le Mans the 917s were quickest in practice. On lap one, privateer John Woolfe crashed his 917 at Maison Blanche and was killed — the first privateer to race a 917. Both works cars retired with mechanical failures. At the final race of the championship season, the 1000 km Zeltweg, Jo Siffert and Kurt Ahrens won in a privately entered 917, giving the car its first victory.
Porsche concluded an agreement with John Wyer and his JWA Gulf Team, which became the official Porsche team and development partner. After the Österreichring aerodynamics breakthrough the 917K became the standard configuration for all races except Le Mans, the Nürburgring 1000 km, and the Targa Florio — where the lighter Porsche 908/03 was used.
At the 1970 24 Hours of Le Mans, Porsche Salzburg, Martini Racing, and JW Automotive all entered. The Porsche Salzburg 917L qualified on pole but retired after 18 hours with engine failure. The winning car was the red-and-white No. 23 917K of Porsche Salzburg, driven by Hans Herrmann and Richard Attwood, which carefully picked its way through pouring rain to score Porsche's first overall Le Mans victory, with only seven classified finishers. Martini's 917LH came in second. A Porsche 908 was third, a Porsche 914-6 sixth (and GT class winner), and a Porsche 911S seventh.
The season began with JW Automotive scoring a 1-2 finish at the Buenos Aires 1000 km, Jo Siffert and Derek Bell leading Pedro Rodríguez and Jackie Oliver home. At the 24 Hours of Daytona, the Roger Penske Ferrari 512M qualified on pole but finished third with mechanical problems behind winners Rodríguez and Oliver. At the 1971 24 Hours of Le Mans, the winning car was the Martini Racing 917K of Helmut Marko and Gijs van Lennep, equipped with a magnesium frame, which set an overall distance record that stood until 2010. Four separate Le Mans track records were broken that year by 917s: fastest qualifying lap, fastest in-race lap, highest top speed, and longest distance covered.
After dominant European results, Porsche focused on the North American Can-Am Challenge. The turbocharged 917/10K entered by Penske Racing won the 1972 series with George Follmer after a testing accident sidelined primary driver Mark Donohue. The 917/30 then dominated the 1973 Can-Am series, winning all races except the Mosport event won by Charlie Kemp and the Road Atlanta event won by George Follmer; Mark Donohue won the rest. McLaren, unable to compete, had already left the series to concentrate on Formula One and the Indianapolis 500. The 917 was the only championship-winning car in Can-Am not powered by Chevrolet.
The SCCA introduced a 3 mpg‑US maximum fuel consumption rule for 1974, effectively ending the 917's competitive career. The Penske 917/30 competed in only one race that year.
In 1981 the Kremer Racing team entered a home-built updated 917, the 917 K-81, at Le Mans, qualifying in the top ten before retiring after seven hours following a collision. The car also ran at Brands Hatch at the end of that season, where it led for a spell before a suspension failure ended its race.
On August 9, 1975, Porsche and Penske took the 917/30 to Talladega to break the FIA closed-circuit speed record. With Mark Donohue driving, the car averaged 221.160 mph (355.923 km/h). It was Donohue's last major accomplishment before his fatal accident in practice for the Austrian Grand Prix a week later. The record stood until 1980.
Many 917 components — chassis, suspension, and brake parts — were used to build the Porsche 936 in 1976. The total production run comprised 43 naturally aspirated cars (36 K, 5 LH, and 2 Spyders) and 16 turbocharged cars (13 917/10 and 3 917/30), for 59 chassis in total. Demand exceeded the original production run of 25, with over 50 chassis ultimately built. At least three 917s were road-registered, including one obtained by Count Gregorio Rossi di Montelera of the Martini company with an Alabama plate to circumvent European certification requirements. The Gulf Oil-liveried 917 Kurzheck coupés were prominently featured in the Steve McQueen film Le Mans, competing against the Ferrari 512.
This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.
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