Relative to this discussion on M-B engines, some points need to be clarified:
1) The M 187 engine was not only equipped with three side draft Solex carburetors but more importantly had a Roots supercharger. Power transmission problems through the existing rear axle arrangement limited use of this application in the racing arena.
2) The M 186 engine was the precursor of the engine installed in the production 300 SL. This engine was notable for having the parting line between the block and the head set at 20 degrees to the horizontal thereby allowing the valve faces to be parallel to the head surface with the combustion chamber existing in the wedge shaped area in the block created by the angular difference between the top of the piston and the parting line.
3) The intake valves were indeed larger than the exhaust valves to maximize flow by capitalizing on the different pressures obtaining during the intake and exhaust strokes. Interestingly enough the valve stems were larger on the smaller diameter exhaust valves to allow room for their hollow sodium salt filled cores intended to improve valve cooling.
4) The 17" runners on the intake manifold were not there for pulse dampening, but rather were created to allow maximum flow at 5500 rpm, a speed that nested comfortably between the maximum torque and horsepower revolutions.
5) The light metal M 198 block first appeared in Chassis Nr. 109.042-10-003049.
6) All M 198 engines in the 300 SL, whether iron block or light metal block, had the injector nozzles installed in the block and the spark plugs installed in the head. The main reason for this configuration was the difficulty encountered in changing spark plugs mounted in the block when the engine itself was inclined 50 degrees to the horizontal in the 300 SL as opposed to the previous upright mounting in passenger cars.