The story of the Alfa Romeo GP Tipo 158 is a testament to the tenacity and ingenuity of the men at Alfa Romeo’s Portello Plant, who cleverly concealed the winning single-seaters during the Second World War, before picking up where they left off and continuing to dominate the premier class of motorsport. But above all, at the heart of the story is a mythical racing car that proved to be a champion from the outset, winning the first Formula 1 World Championship at a canter.
After parting ways with Enzo Ferrari, whose Scuderia Ferrari division had been the acting racing team for Alfa Romeo, the firm's original plant in Portello founded its own in-house racing department, Alfa Corse, which was based in Milan. It focused on designing a new car with a supercharged engine in the 1.5-litre Voiturette class, which was to become the leading class from 1940. The team, led by Gioachino Colombo, sketched out the lines of the GP Tipo 158, soon to be nicknamed the Alfetta (Little Alfa).
The engine was an innovative straight-eight design with dual blocks in light alloy, screw-in steel bores, double overhead camshafts driven by a cascade of gears and a fuel system featuring a Roots supercharger. The gearbox was integrated with the differential and mounted on the rear axle, for perfect weight distribution. The power output of the first version was 195 hp, but in 1939 this was increased to 225 hp with a top speed of 232 km/h.
The Alfetta dazzled the public with a 1-2 finish on its debut in the 1938 Coppa Ciano, but its career already seemed to be over following the Tripoli GP in 1940, when all competitions were halted by the outbreak of war. With farsightedness, however, Alfa Romeo managed to hide the cars under a fake wood-pile on a pig farm near Milan, to avoid discovery by German army search parties.