The Voisin C6 was a racecar built in 1923.
Due to the imaginative interpretation of the race regulations, that had helped Gabriel Voisin secure such a convincing victory in the touring car class of the 1922 French Grand Prix, a rule imposing a minimum frontal area was introduced for the following year.
Six months was taken to design, construct and test the competitive car. Despite the fact that sleeve valve engines were less than ideal for track racing, a 2-litre straight six was used.
Voisin asked André Lefebvre to design an ultra-light and aerodynamically efficient body to compensate for the new engine's modest power output. The result was truly extraordinary.
It had the first true monocoque chassis, constructed from aluminium panels over an ash frame. The underside was completely flat, with the profile of an aerofoil section.
The 2-litre engine produced about 75bhp. It underwent trials during which high speed cooling problems were resolved by adding an external airscrew to drive the water pump without sapping engine power. Propelled by the air, it started to work at speeds over 50kph.
The C6 failed to shine, its many technological innovations were unable to compensate for the sheer lack of power it's engine.
Only one of the four-car team survived the race, André Lefebvre bringing car No.10 into 5th place at an average speed of 63.2 mph.