BMW M10 “Apfelbeck” - Radial Valve Engine for Formula 2
In 1966, a new Formula 2 racing engine derived from the BMW M10 was finished with a new four-valve cylinder head invented by Ludwig Apfelbeck. Derived from the production engine of the BMW 2000, the DOHC 16V 2 liter engine had Kugelfischer mechanical fuel injection and a flat-slide throttle system.
The engine capacity was 1990 cm3 (bore x stroke : 89 mm x 80 mm ), its maximum torque of 236 Nm achieved at 8000 RPM. Maximum power (260 hp) specified at 8500 RPM.
The theoretical benefits of the Apfelbeck cylinder head design consisted of a very good charge cycle through higher valve lift and thermal resistance due to the non-adjacent exhaust valves. The drawbacks of this motor were due to an unfavorable ratio of hub bore and channel diameters as well as the extremely complex valve train. Also, because of the large volume of the hemispherical combustion chamber, the elevation of the piston crown had to be increased to acheive a good compression ratio, and this in turn increased piston weight. In addition, while this engine had fantastic cylinder filling ability at high RPMs, power was sacrificed in the low and mid RPMs due to low air velocity because the intake runners and valves were so gigantic. Therefore, this motor did not have very much success in racing, apart from some fantastic acceleration runs.