Background
The acquisition of the Dixi works at Eisenach in 1928 provided BMW, hitherto a manufacturer of aero engines and motorcycles, with a foothold in motor manufacturing. Dixi's built-under-license version of the Austin Seven was gradually developed and improved, ending up with swing-axle suspension and overhead valves, and then in 1933 came the first true BMW: the six-cylinder 303.
The latter adopted a twin-tube frame and abandoned the rear swing axles in favour of a conventional live axle, while up front there was a superior transverse-leaf independent suspension and rack-and-pinion steering. These features, along with the four-bearing, overhead-valve engine, would provide the basis for the more powerful sporting models to follow.
Introduced in 1938, the 327 sports-tourer used the shortened, boxed, ladder-type chassis of the 326 saloon, shared by the 320, but with semi-elliptic rear springing in place of torsion bars. The gearbox was a Hurth four-speed manual unit with freewheel between 1st and 2nd gears, enabling clutch-less gear changes at low speeds, while hydraulic brakes were fitted all round.
BMW's pushrod six had by now been enlarged to 1,971cc and developed around 55bhp in the 327, which could also be ordered with the 328 sports car's engine at extra cost. The 328's engine featured an ingenious new cylinder head, designed by Rudolf Schleicher, which incorporated hemispherical combustion chambers and inclined valves without recourse to overhead, or twin, camshafts.
Instead, the 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.
Downdraft inlet ports contributed to the motor's deep breathing, and its tune-ability made it a popular choice for British racing car constructors, most notably Cooper, during the 1950s. The 328 engine produced 80bhp, an exemplary output for a normally aspirated 2.0-litre unit at that time, with more available in race trim.
Deploying the 328's state-of-the-art engine in a more civilised and comfortable package, the 327/28 is relatively rare, with only 428 completed up to 1940 when production ceased.
