Abstract: A passive secondary air muffler for a small internal combustion engine. The secondary air muffler may include a venturi device and a catalytic converter. The venturi device may be in the form of a stamped sheet metal insert which, along with the outer muffler housing or shell, forms a secondary or auxiliary air intake device. The venturi device may also be formed from baffles separating an inlet chamber from an outlet chamber of the muffler. The secondary air intake device provides auxiliary or secondary air to the exhaust gas stream exiting the engine upstream of the catalytic converter to improve the efficiency of the catalytic converter. In an exemplary embodiment, the venturi device has a hemispherical cross-sectional shape or a circular cross-sectional shape taken along a plane substantially perpendicular to the direction of flow of the exhaust gas stream.

Abstract: A passive secondary air muffler for a small internal combustion engine. The secondary air muffler may include a venturi device and a catalytic converter. The venturi device may be in the form of a stamped sheet metal insert which, along with the outer muffler housing or shell, forms a secondary or auxiliary air intake device. The venturi device may also be formed from baffles separating an inlet chamber from an outlet chamber of the muffler. The secondary air intake device provides auxiliary or secondary air to the exhaust gas stream exiting the engine upstream of the catalytic converter to improve the efficiency of the catalytic converter. In an exemplary embodiment, the venturi device has a hemispherical cross-sectional shape or a circular cross-sectional shape taken along a plane substantially perpendicular to the direction of flow of the exhaust gas stream.

Abstract: The present invention provides a tuned muffler for small, single cylinder internal combustion engines, particularly 4-cycle engines. The muffler includes a first shell having an exhaust inlet, a central plate, and a second shell having an exhaust outlet. The central plate is disposed between the first and second shells, and the foregoing components define an exhaust path therethrough which includes a first expansion volume, a first passage, a second expansion volume, and a second passage. The first and second expansion volumes and the first and second passages are dimensioned to provide an exhaust tuning effect to enhance engine performance, and also to provide an exhaust flow path which conducts the exhaust gas smoothly through the muffler to substantially reduce back pressure within the muffler.