At the end of the 1971 season, the coupe bodied Porsche 917 was no longer eligible to race in the world championship, which saw the German manufacturer's focus shift to the Group 7 class. In open form the 917 had been campaigned in this virtually no limits class since 1969, but with little factory support. Two championships were open for the Group 7 cars; the European Interserie and more importantly the North American CanAm Challenge. Big engines, low weight and a host of different looking vehicles had made CanAm one of America's premier classes, attracting many spectators.
Porsche was represented in CanAm for a number of years by privateers who race 908s or decapitated 917s, until a purpose built Group 7 version of the 917 made its debut in 1971. Dubbed the 917/10, it was technically similar to the coupe 917, but featured a number of lighter components constructed from the latest exotic materials. A larger fuel tank was also fitted to enable the car to complete the 200 mile races without having to refuel. Completely new was the spyder bodywork, which was an adaptation of the contemporary CanAm design.
A few races into the 1971 season, the Porsche 917/10 made its debut in the McLaren dominated series. It was immediately obvious that the 5 litre flat 12 was not powerful to take on the might of the all-alloy Chevrolet V8s, but nonetheless valuable points were scored in the car's first season. Back in Germany two options to close the gap with the 800 bhp V8s were considered; a 16 cylinder version of the 917 or fitting turbochargers to the existing engine. The second option was by far not as easy as it sounds today, but it was expected to offer the best performance so it was fully explored.
In the preceding fifty years racing cars were either naturally aspirated or equipped with a supercharger driven by the crank; exhaust driven turbochargers was uncharted territory. Throttle lag was the biggest problem to overcome with turbos. In order to operate ideally the turbines in the turbo had to run at a specific speed, but that requires a minimum amount of engine revolutions. When the engine was running under that number, there was considerably less power, and when the turbos did kick in it was not a gentle affair. Drivers of the turbocharged 917s needed to have a very delicate right foot and stellar reflexes to cope with the sudden power increases.
In five litre form, the turbocharged flat 12 was good for around 950 bhp; not for the faint of heart. In Mark Donohue and George Follmer Porsche found two drivers brave enough to take on the competition in their 917/10K. Donohue proved to be the faster of the two, but an accident early in the season left him out for most of the remaining races. This paved the way for George Follmer to finally challenge and beat the McLarens and secure the championship. In Europe the 917/10Ks were campaigned in 4.5 litre form, but it was still enough to clinch a one-two in the championship.
Although the McLarens were convincingly beaten in 1972, Porsche continued the development and constructed the most powerful racing car ever. Available only for Team Penske's driver Mark Donohue, the 917/30 was bigger in every aspect compared to the 1972 racer. The engine's displacement was increased to 5.4 litre, which saw the performance rise to at least 1100 bhp in race trim. A new longer and aerodynamically efficient body was fitted, which increased the top speed considerably. In the 1973 season there was no stopping the 'Turbo Panzer', and Mark Donohue won the championship.
As a side effect of the Porsche dominance, CanAm was quickly losing teams and spectators and halfway through the 1974 season the challenge was cancelled. Porsche had also withdrawn at the end of the 1973, but the 917/30 was given one final outing in 1975. Specifically prepared for a high speed run, Donohue lapped the Talladega race track at an average of 221 mph in the 917/30, setting a new world record. A fitting finale for the Porsche 917's magnificent career. Unfortunately it was also the finale of Donohue's career, who fatally crashed ten days later during Formula 1 qualifying in Austria.
-Article by Wouter Melissen
General specifications
Country of origin: Germany
Produced in: 1973
Numbers built: 4
Weight: 849 kilo / 1871.7 lbs
Drivetrain
Engine: 912.52 180º V 12
Engine Location: Mid , longitudinally mounted
Displacement: 5.374 liter / 327.9 cu in
Valvetrain: 2 valves / cylinder, DOHC
Fuel feed: Bosch Fuel injection
Aspiration: Twin Eberspacher turbos
Gearbox: Type 920 4 speed Manual
Drive: Rear wheel drive
Performance figures
Power: 1100 bhp / 821 KW @ 7800 rpm
Torque: 1112 Nm / 820 ft lbs @ 6400 rpm
BHP/Liter: 205 bhp / liter
Power to weight ratio: 1.3 bhp / kg
Top Speed: 386 km/h / 240 mph
0-60 mph Acceleration: 2.1 s
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Originally Posted by amat
