A turbo charging assembly particularly suited to motorcycles and requiring litle modification of a normally aspired engine for fitment. The assembly includes a turbine/compressor unit (1 and 2) and a narrow plenum chamber (4) leading to the inlet of a carburettor (5) in the standard carburettor position. The carburettor is not particularly adapted for super charged aspiration but is of conventional design. The plenum chamber (4) includes an air dump valve (8) opened by high intake vacuum such as occurs during engine overrun. The air filter (11) is attached directly to the compressor (1) inlet.