In the late 1960s, the FIA created a new category of racers in a bid to draw more competitors to the World Sportscar Championship (WSC). To be eligible to compete in the new category, cars had to weigh at least 1,763 pounds and have an engine with a displacement of under 5.0 liters. Additionally, manufacturers needed to build just 25 examples of each car, significantly less than the 50 examples that were required in the above-5.0 liter class. The looser requirements made competing in the WSC cheaper and accessible to smaller teams.
With these guidelines in mind, Porsche began developing an evolution of the 908 called 917 in June of 1968. The project was controversial in Stuttgart because Porsche was still a rather small company at the time so it had considerably fewer resources at its disposal than rivals like Ford and Ferrari. However, a group of executives that included Ferdinand Piëch enthusiastically supported the project because they believed the 917 would pay for itself in the long run.
Porsche applied the lessons it had learned from the successful 908 to the 917. The new car’s body was crafted out of fiberglass, the windows were made out of Plexiglas and the chassis was built using aluminum. All told, the first 917 tipped the scale at 1,829 pounds.
Power for the 917 came from a 180-degree 4.5-liter flat-12 engine that made 520 horsepower at 8,000 rpm and 339 pound-feet of torque at 6,800 rpm in its initial state of tune. The engine was essentially two 911-sourced flat-six units fused together. It was air-cooled, a decision that is often attributed to Piëch who famously claimed it was possible for a car to develop a coolant leak but it was impossible to lose air. It took about three percent of the engine’s power, or about 17 horsepower, to spin the massive vertical fan.
The 917 was presented to the public and the press at the 1969 edition of the Geneva Motor Show. The 25 cars required for homologation were displayed outside of Porsche’s Zuffenhausen factory in April of that year, and the 917 was granted permission to race on May 1st.
In spite of the engineering might that went into its development, the 917 proved remarkably difficult to control at high speeds and many pilots simply refused to drive it. The handling issues were made painfully evident when a British privateer named John Woolfe died after his 917 turned over during the first lap of the 1969 24 Hours of Le Mans. The 917 nonetheless managed to grab its first win in August of 1969 at the 1000 kilometer race that was held on Austria’s Österreichring.
Porsche teamed up with John Wyer Automotive to make much-needed modifications to the 917’s body in order to increase its high-speed stability. For 1970, the 917 could be fitted with one of two rear ends, a short one that was ideal for twisty tracks and a longer one that was designed for circuits like Le Mans with long high-speed stretches. The short models were called K (for kurzheck, short tail in German) while the longer variants were known as L (langheck, long tail in German).
The updates turned the 917 into one of the most successful race cars ever built. A 917 K wearing number 23 won the 1970 edition of the 24 Hours of Le Mans, beating the 512 that had been designed by Ferrari specifically to defeat Porsche. One of the highlights of the race came when a 917 driven by Vic Elford hit a record-setting top speed of approximately 240 mph on the Mulsanne Straight. Footage from the 1970 race was used in Steve McQueen’s famous Le Mans film.
Other victories quickly followed. The 917 took first at the 24 Hours of Daytona, the 1000 kms of Brands Hatch and the 1000 kms of Monza, among others, allowing Porsche to win the 1970 International Championship for Makes.
The 917 won Le Mans again in 1971 and Porsche went on to take first place in the International Championship for Makes for the second year in a row. However, the success was bittersweet because the category that the 917 competed in was scheduled to be phased out at the end of the 1971 season and the FIA opted not to renew it. Porsche had a lot invested in the 917 program and it wasn’t going to simply call it quits. Modified 917s had been racing in the Canadian-American Challenge Cup (Can-Am) since 1969 so the Porsche shifted its focus to winning on the other side of the Atlantic.
The 917 hadn’t been very successful in the United States because it was outgunned by Chevrolet-powered McLarens and Lolas. Porsche briefly experimented with a 180-degree 16-cylinder engine whose displacement could vary between 6.0 and 7.2 liters, but the project was ultimately canceled because the long wheelbase required to fit the engine worsened handling. Determined to win at all costs, Porsche squeezed nearly 1,000 horsepower out of the flat-12 by bumping its displacement up to 5.0-liters and fitting it with two large turbochargers. The upgrades helped the 917 fend off the competition and take first place overall in the 1972 Can-Am series.
The following year, Porsche introduced an even more powerful evolution of the 917 called 917/30 that packed a 5.4-liter variant of the flat-12 tuned to make approximately 1,100 horsepower at 7,800 rpm and 809 lb-ft. of torque at 6,400 rpm in standard race tune. Thanks in part to a low weight of about 1,760 pounds, the 917/30 hit 60 mph from a stop in 2.1 seconds — in first gear, no less — and went on to a top speed of over 250 mph. The car was equipped with two fuel tanks that offered a combined capacity of 105 gallons.
The 917/30 was unbeatable. Penske Racing’s 917/30 easily took first overall in the 1973 Can-Am season, and the less powerful 917/10 took second, third and fourth place overall. Unfortunately for Porsche, the 917’s success was again cut short. In response to the global oil crisis, Can-Am implemented a number of gas mileage regulations in 1974 that the 917 could not comply with, and the series was canceled altogether after the Road America race that took place on August 24th, 1974. The 917 won Germany’s Interseries the following year but it retired after.
Porsche built a total of 65 917s. 44 were short- and long-tail coupes, two were PA Spyders and 19 were cars built for Can-Am and the Interseries. The 917 had no direct successor, but the forced-induction technology trickled down to the 911 Turbo.