The SM Roadster – a progression of the Nine Roadster – came along in 1951 to fight against MG’s TD model, a car it bore rather a striking resemblance to. With an SM1500 overhead-cam engine reduced in size to 1497cc (to allow it to enter under-1500cc motorsport events), it had less power than the MG but similar performance thanks to its light weight. However, the battle lines were more evenly drawn from 1952 when twin carburettors became an option. With the extra carb, 58bhp was the more satisfying output. Some cars had bodies by Bertone, but these are very rare.
info from Octane