Although there was undoubtedly a significant input from the bright aeronautical engineers at Bristol, the 400, which commenced production in 1947, was effectively a synthesis of three pre-war BMW designs, with a chassis derived from that of the 326, an engine from the 328 sports car and an aerodynamic bodyshell similar to that of the 327 coupé.

The 1,971cc six-cylinder engine of the BMW 328 featured an ingenious new cylinder head, designed by Rudolf Schleicher, incorporating hemispherical combustion chambers and inclined valves without recourse to overhead, or twin camshafts.

Instead, the Type 319 engine's single block-mounted camshaft and pushrod valve actuation were retained, thus avoiding an expensive redesign.

Two rocker shafts were employed, one situated above each bank of valves, giving the engine an external appearance almost indistinguishable from that of a twin-overhead-cam design.

Downdraught inlet ports contributed to the motor's deep breathing, and its tunability made i...