Abstract: The invention comprises an exhaust system for a motorcycle engine which has an outer imperforate casing having a substantially elliptical cross-section and an inner, coaxial, perforate sleeve also of elliptical cross-section which is of lesser dimensions to provide an annulus within the casing which is packed with a gas permeable material, high temperature resistant material such as fiberglass. The muffler has a single piece inlet end cap and a single piece outlet end cap. Each end cap has an elliptical flange over which is received an end of the outer casing of the muffler. The end caps also have integral mounting flanges to receive and support the inner perforate sleeve. Preferably the muffler is provided with a replaceable sound choke which is a small diameter sleeve that can be removably secured in the discharge end of the muffler, thereby permitting the muffler to be switched between restricted off-road use and unrestricted off-road use.