M124

In 1939 Daimler-Benz built experimental straight-eights derived from the M24 of the 540 K, opening the bore by 7 mm and shortening the stroke by 5 mm for just under 5.7 liters. Cast-iron block and head, gear-driven twin overhead camshafts, dry-sump lubrication, a Roots blower and a carburetor: around 130 PS unblown and 200 PS with the supercharger engaged, both at 3,400 rpm. A few short-chassis prototypes were bodied as sports coupés and roadsters and given the internal series number W129.

Ever since, the literature has called that car the 580 K and the intended successor to the 540 K, stopped only by the war. Mercedes-Benz’s own historians reject the story. They point out that the experimental engines were barely developed at all, and that Untertürkheim was by then well advanced on two new V12s, the M148 and M157 — which suggests the big straight-eight was being wound down rather than renewed. Stuttgart calls the 580 K a phantom model, and the M124 is what is left of it.