The Porsche 917 is without question one of the most famous racing cars in history. The background to the development of the car, which was initially labelled "undriveable" even by seasoned racing drivers, and with which Porsche achieved its first overall victory at Le Mans in 1970, is legendary. The 917 in Gulf livery was made legendary by Steve McQueen in the 1971 film "Le Mans".

The last use of a 917 at Le Mans ten years later is rather unknown. According to Wikipedia:"The last known use of a Porsche 917 outside of historic racing was in 1981, when the Cologne-based Kremer racing team had collected enough vehicle components over the years to build a complete Porsche 917.

It was a short-tail coupé with vertical stabilising fins at the rear and a one-piece wing in between - similar to the design last used on the CanAm Spyders. The car was equipped with a 4.5-litre naturally aspirated engine and bore the official designation Kremer-Porsche 917 K81."

Gallery: 1981 Porsche 917 K-81

K81 is now available for purchase: RM Sotheby's is pleased to announce the consignment of the Porsche 917K Chassis 917-K81 for the upcoming auction in Monaco, which will take place from 10-11 May at the Grimaldi Forum. This historic Porsche 917 K-81 from 1981 is the last chassis built with the factory's blessing. It is estimated at £3,000,000 - £4,300,000.

The 917-K81 chassis played a pivotal role in one of motorsport's greatest underdog stories when it heralded the return of the 917 to the premier class of endurance racing in 1981 after a 12-year absence, capitalising on a brief window of opportunity before the introduction of Group C regulations in 1982.

The car was built by Kremer Racing with the support of the Porsche factory, which provided the Cologne-based team with the chassis schematics together with flat-bodied V12 Type 912 engines.

1981 Porsche 917 K-81
1981 Porsche 917 K-81

During the development of the 917 in the late 1960s, the new twelve-cylinder engine broke with the tradition of the boxer engine at Porsche for the first time, as it was a V-engine with a bank angle of 180 degrees. The shorter overall length compared to a comparable boxer engine and the reduced frictional power due to the smaller number of crankshaft main bearings are arguments in favour of the V12 design. Hans Mezger developed the twelve-cylinder engine with a displacement of 4,494 cubic centimetres using the performance parts from the 3-litre engine of the 908 - pistons, cylinders and valves.

Special design features of the new racing engine, equipped with dry sump lubrication, are the lightweight magnesium housing and the centre output for driving the two overhead camshafts per cylinder bank via gear wheels. Like all previous Porsche engines, it is air-cooled and has a horizontal blower. The mixture is prepared by mechanical intake manifold injection with a 12-piston double-row injection pump from Bosch.

1981 Porsche 917 K-81

The engine designation Type 912 is derived from the more recent nomenclature of various Porsche racing cars, in which the vehicle designation also included the respective number of cylinders of the engine - 904, 906 and 908. The overall vehicle and also the five-speed gearbox, on the other hand, were given the type designation 917.

But back to the K81. Thanks to advances in tyre technology and aerodynamics, the car became the most modern 917 ever built. In 1981, it took part in the 24 Hours of Le Mans with Bob Wollek, Xavier Lapeyre and Guy Chasseuil. Despite a 9th place finish, the car was unable to realise its full potential due to a lack of development and was eventually withdrawn from the race due to a damaged oil supply.

The car took part in the 1,000 kilometres of Brands Hatch in 1981, where it qualified in 3rd place with Bob Wollek at the wheel and finally showed its true pace. Wollek took the lead in the middle of the race before retiring nine laps later. The race marked the end of the 917-K81 chassis' short racing career and ended the illustrious history of one of the most dominant and famous models ever used in endurance racing.

This car is being offered again for the first time in over a decade and offers an extremely rare opportunity to acquire one of the most fascinating and historically significant Porsche 917s.