With new Grand Prix regulations for the years 1938 to 1940, the motorsport authorities in Paris again attempted some damage limitation. The displacement for the elite sport was cut back to 3 litres, or 4.5 litres in the case of vehicles without a compressor – a reduction of around 50 per cent for Mercedes-Benz.
The racing department in Untertürkheim, which was still competing on many fronts, definitively became a think-tank. Concepts with front- and rear-mounted engines with eight, twelve and even 24 cylinders were repeatedly drafted and discarded. Even two suggestions from Ferdinand Porsche and an injection engine were discussed. Finally, the team decided upon a V12 initially charged using two Roots-type blowers, before these were superseded in 1939 by a two-stage compressor. Employee Albert Heeß was the man behind it. He created a technological masterpiece with a cylinder bank angle of 60 degrees, two overhead camshafts each, four-valve cylinder heads and an auxiliary carburettor that cut in at high engine speeds.