OM “Superba 665 SSMM” – 1931
The 665 Superba was introduced in 1923 and produced in several series and models until 1932. It was the best known and appreciated OM production model because of its racing wins, culminated in the first three positions at the first edition of the Mille Miglia in 1927. After the victory of the Alfa Romeo in the 1928 Mille Miglia, OM realised the importance of the supercharger and in 1929 introduced a new sports model with a Roots supercharger. From then on, OM models were available with or without supercharger, with over-head or side valves. The car on show in the museum is a 665 SSMM model; fitted with a Roots supercharger, is one of the cars the English OM importer modified, fitting cylinder heads with over-head instead of sides valves.
The English heads were cast iron and the combustion side was “flat”. Domed pistons, because the low position of the sparkplugs did not leave room for trunk pistons. The cyclinder block was very special, made in cast iron with twelve 18mm sparkplugs, six on each side fixed in well-hidden holes. In the road version ignition was supplied with magneto, coil ignition and 6 cylinder spark coil. The racing models probably used two magnetos for double ignition. Thanks to the light and well shaped body built by Carrozzeria Castagna, the car could reach a speed of 150 kph.