People who know me always think it's odd that my favorite air-cooled Porsche of all time is one which most Porsche enthusiasts have never heard of. In any case I have admired this thing more than the 356, 718, 911, 917-30, or other notable air-cooled models. The Porsche 909 "Bergspyder" was designed for hill climb racing. Porsche had to make this car as light as possible and give it an outrageous power-to-weight ratio. The car was designed to run for only a few minutes and make its way up a hill so many compromises could be made.
The brake discs were made from chrome-plated beryllium and were 75% lighter than standard brakes. The 909 chassis was an ultra lightweight aluminum space frame. The suspension used custom made titanium springs. The car's electrical system uses much lighter silver instead of standard copper for wire. In a further extreme weight-saving measure all the hardware was titanium or aluminum: no steel fasteners anywhere are used in this car's chassis.
In the quest for weight savings the Porsche 909 has no fuel pump. Instead of a pump Porsche used a pressurized 4-gallon tank which was built like an aircraft hydraulic accumulator. One side is pressurized with nitrogen and the other side is filled with fuel. When pressurized the nitrogen pushes against a rubber interface which then pushes against the fuel.
The Porsche 909 engine was built using Porsche's experience in Formula 1 racing. This little 2.0 DOHC flat eight cylinder engine puts out 275 horsepower at 9,200 RPM. The engine sucked air in through four Weber carbs. It was similar to the engine used in the 718, 904, 906, 908, and 910. These engines were hand built artwork and Porsche used their finest engine builders to construct them.
Here's a little video which shows you the wonderful music the little 2.0 litre flat-8 motor makes:
Covering all of this is an ultra lightweight fiberglass shell so thin that it was translucent before getting painted. What is the final result of all of this extreme weight saving measure? The 909 only weighed 850 lbs empty. Adding fuel and driver made the final weight right about 1,000 lbs. Remember that it had 275 horsepower to propel it. This ultra lightweight car unfortunately had few safety features and driver Ludovico Scarfiotti was killed when his 909 flew off the road and crashed. His death marked an end for the program.
Porsche learned a lot from the 909 program and used many of the techniques in their later racing cars. The chassis set the design standard which Porsche would use for the immensely successful 956 and 962 years later. Simply put the 909 was far ahead of its time and a stellar example of Porsche's perfectionist approach to engineering. This car always has been and always will be my favorite air-cooled Porsche.