The 12C-36 made its debut in Tripoli Grand Prix 1936, and the 12C-37 in Coppa Acerbo 1937.

The 12C-37 was a new car, with a lower chassis and an engine bored and stroked to 4475 cc, now with roller- instead of plain bearings and two smaller superchargers instead of a single large one.

The car suffered poor handling, which could not be cured in time for the 1937 Italian GP, and thus was not successful.

Four examples of the 12C-37 were built, although only two were actually assembled for the 1937 Coppa Acerbo and Italian GP.

The four 12C-37 chassis were instead assembled into 312 (V12 downsized to 3-litre) and 316 (V16 obtained from two 158 engines fitted to a common crankcase) formula race cars.