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Porsche 917 Can-Am Turbos
The North American Can-Am series featured sprint races run to FIA Group 7 rules, which placed very few limits on the cars. There was no minimum weight and no limit on engine size. Porsche saw it as a development and promotional opportunity in their largest export market. The 917 engines could grow to 5.4 liter capacity, but that was nowhere near the 8-liter, Chevrolet- based monsters that dominated in Can-Am racing. Porsche turned to a new and important solution – exhaust-driven turbocharging. The concept had been around for decades, particularly in aircraft, and successfully applied in oval-track racing. However, to apply it in sports car racing, where engine speeds are highly variable, was a tremendous challenge.
Porsche employed one turbocharger for each cylinder bank of the 917’s flat-twelve, initially using the 4.5-liter version, but eventually moving to the 5-liter for the 917/10 used during the 1972 season. The engine was capable of delivering about 1,000 horsepower, depending on boost. However, fuel metering through the mechanical injection system proved to be a significant challenge when adapting the proven 917 engine to forced induction. In the pre-electronic era, ‘mapping’ of the fuel/air mixture had to be achieved by mechanical means, plus there had to be a reliable system for maintaining air flow in the induction system at low rpm while relieving excess pressure at high rpm. Turbo ‘lag’ (where the increase in power is delayed slightly while the turbochargers build up boost pressure) required the drivers to adapt their driving style, including the use of left-foot braking while keeping the throttle open to maintain boost level.
Porsche selected the Roger Penske organization to conduct the official factory race operations in the 1972 and 1973 Can-Am series. 917/10 spyders were sold to other teams (initially with 5.4-liter, non-turbo engines). Penske’s driver/engineer, Mark Donohue, proved invaluable in assisting with the development
of the 917/10. In addition to engine development, the aerodynamics of the body shape and the suspension geometry were substantially revised in collaboration between Porsche and Penske. After finishing second in the first race at Mosport
1970s
Family Business
By 1970, tensions and rivalries within the Porsche and Piëch families became a significant concern for the future of the company. With eight of Dr. Porsche’s grandchildren as shareholders, it was natural that there might be differences of opinion, ambition and talents for those taking an active role in managing the family business. Between the autumn of 1970 and the spring of 1972 a gradual series of changes largely resolved the issues.
The family members all agreed to withdraw from day-to- day roles in running the company. The new rule was that all had to agree to any one member returning to an active role (which was unlikely). Ernst Fuhrmann, father of the four-cam engine, returned to Porsche eventually becoming head of the management board (CEO). Heinz Branitzki succeeded Hans Kern as head of finance and commercial departments. Helmuth Bott became head of R&D. The families formed Porsche GmbH as a holding company for shares in Porsche KG (the limited partnership) which converted to Porsche AG (stock company) by the end of 1972. Ferry Porsche was chairman of the supervisory board from that point forward.
Author Karl Ludvigsen quotes Ferdinand Piëch regarding the improved family relations in Excellence Was Expected: “We’re happy to meet with each other at all the relevant birthdays and various festivities. We still have our ups and downs, but not so angrily.”
PORSCHE POINTS
tBefore committing to turbocharging for its 917 Can-Am cars, Porsche experimented with a 16-cylinder version of the Type 912, flat-12. Possible capacities ranged from 6 to 7.2 liters. A surviving 16-cylinder engine resides in 917 Chassis 027 at the Porsche Museum.
tPenske racing secretly provided a McLaren M8D (Denny Hulme’s 1970 car) to Porsche in November 1971, for evaluation at Weissach during the development of the 917/10.
tValentin Schäffer, Porsche’s ace mechanic-turned-engineer, was a key collaborator with Hans Mezger from the beginning of Porsche’s work on turbocharged engines, starting with the 917/10. Schäffer adapted the IndyCar, AiResearch pressure-relief valve to limit maximum boost in the first 917 turbos. As early as 1969, Schäffer had experimented with a turbo engine in a 911.
PORSCHE DECADES 1970s
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