Abstract: A device for securement to or incorporating into the exhaust assembly of an internal combustion engine to improve efficiency thereof is disclosed. The device comprises a generally tubular housing open at both ends to enable passage of exhaust gases and a flow of air therethrough, and an axle coaxially positioned within the housing on a laterally extending support member, and a hub rotatably mounted on the axle, and two identical and opposed radially extending blades secured to the hub, the blades being obliquely angled with respect to the longitudinal axis of the hub, at least the forward edge of each blade extending inwardly providing inwardly pointing projections. In preferred construction, the inwardly pointing projection is formed between the forward edge of the blade and a forward inner edge of the blade, the said edges defining therebetween an angle of about 66.degree. - 67.degree.. In a further embodiment, at least the leading portion of each blade lies in a plane at an angle of about 72.degree.