In October 1967, the FIA decided to raise the capacity limit for Constructors’ World Championship sports racing cars from 3 to 5 liters for the ‘68 season. Porsche had so far competed successfully with its 3 liter 908. But now things were to change drastically. Ferrari was immediately preparing 5 liter cars, and Porsche had to follow soon.

We show you here on my pen drawings the engine in its early 4,5 liter configuration…with both cylinder banks being tucked away in the chassis,  only the induction pipes and cooling turbine are clearly visible.  

The result was the 917. In July 1968, development started. Initially, the capacity was limited to 4,5 liter for a very good reason: one could use the same cylinders, pistons, conrods, valves, cylinder head and combustion chamber dimensions, ignition and injection systems as the well proven 8 cylinder 3 liter racing engine of the 908. A sound basis to start with. The chassis was also mainly based on the 908.02. And so on March 13, 1969, the 917 was unveiled at the Geneva Motor Show. The price of this racing car: a mere 140.000 Mark, and already at the end of April the necessary 25 units for homologation by the CSI commission were built. It is no secret that the whole cost for Porsche of building the 917 and its racing preparation boiled down to 350.000 Mark per car…

The biggest early success was the Le Mans win on 14 June 1970, with Hans Herrmann/Richard Attwood in the 917 short tail painted in the red and white Porsche Salzburg colors.

 

The engine is air cooled with two flat cylinder banks, four overhead cams and fuel injection. As said, bore and stroke of 85 x 66 mm were identical to the 908. Power was taken from the center of the crankshaft, through a straight cut 31 tooth gear. The engine block was made from magnesium alloy, and the engine was cooled through an axial turbine with 33 cm diameter, able to push through 2700 liters of air per second at max. power rpm of 8400 rpm. Of course, there was a newly developed 12 port injection pump. Maximum power was 460 HP, with a massive 50 mkg torque being available at 6800 rpm.

In April 1970, engine capacity was already enlarged from the initial 4494 cc to 4907 cc, with now 86 mm bore and a lengthened stroke from 66 to 70,4 mm. 600 HP were available at 8400 rpm, torque being also raised to 56 mkg.

Later on, turbo versions were to follow, and the most powerful version of this magnificent engine was the 5374 cc version which made its appearance in 1973 in the Can Am 917/30 Spyder, delivering 1100 HP at 7800 rpm, torque being 112 mkg at 6400 rpm.

 

Hans Knol ten Bensel