Voisin Laboratoire

The Voisin Laboratoire, known first as the Voisin C6 Course and later as the Laboratoire, was a racing car that Avions Voisin built for the 1923 French Grand Prix at Tours. When the Automobile Club de France published fixed body dimensions for the 1923 touring car race, Gabriel Voisin objected in an open letter and entered four cars in the Grand Prix de Vitesse instead, which left the firm about five months to build them from scratch. Rival engines with overhead camshafts could turn faster and make more power, so the team tried to make up the difference with low weight and low drag, using its aircraft experience. The car had no conventional chassis: its structure was a box of light ash framing covered with aluminium panels and a flat aluminium undershield, which makes it one of the earliest racing cars of monocoque construction. The body was long and tapered with the rear wheels inboard, the rear track was 75 cm against 145 cm at the front, and the differential gears were left out to save weight. Power came from a six-cylinder sleeve-valve engine of about two litres, cooled by a thermosyphon system with a small water pump driven by a tiny air propeller above the radiator. Drivers were told not to exceed 4000 rpm, which limited output to about 75 bhp and top speed to just under 175 km/h, so the cars were outclassed by the power of their rivals. André Lefebvre was project manager and responsible for building the cars.