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.

This is given as the reason for Vittorio Jano's resignation from Alfa Romeo at the end of 1937.

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.