US Patent 7146806 Internal combustion engine cylinder and muffler assembly with catalytic converter

A two cycle internal combustion engine cylinder having a piston chamber. The cylinder includes transfer ports; and an exhaust port divided into at least two sections. A first one of the sections has an aperture at the piston chamber with a top surface located closer to a top of the piston chamber than a top surface of an aperture of a second one of the sections at the piston chamber. The first section has a cross-sectional area which is smaller than a cross-sectional area of the second section. The aperture into the first section is located further away from the transfer ports than the aperture into the second section.