Abstract: In a two-stroke internal combustion engine with at least one cylinder opeg into an exhaust passage with a diffuser-type flare whose shape is determined mainly by that of the lower contour, an optimum flow pattern in the exhaust passage is obtained by providing the exhaust passage with a nozzle-like throat in the immediate vicinity of the cylinder, which is formed by the lower contour and is followed by the diffuser-type flare, either immediately or at a distance.

Abstract: In an exhaust system for two-stroke cycle engines, comprising an exhaust pipe whose front end, which is characterised by a constant cross-section, is followed by two or more conical sections, these conical sections are configured as diffusers, which are connected to the front end of the exhaust pipe with its constant cross-section by means of branch pipes of different length, and which open into a common exhaust header at the other end, which header in turn is connected to the exhaust tail pipe comprising a catalytic converter and/or a silencer. This arrangement has the effect that a pressure wave coming from the cylinder is twice reflected as a suction wave arriving at the still open exhaust port at different times due to the difference in pipe length. In this manner the effective duration of the suction wave is prolonged over that of comparable exhaust systems of a known kind.