Abstract: An exhaust system for an internal combustion engine. A plenum chamber has two ports, one which is connected to a header tube for conducting a stream of exhaust gas and another which is connected to a ram tube adapted to collect outside air provided by movement of a vehicle in which the internal combustion engine is installed. The plenum chamber is constructed so that the outside air is caused to travel thereinside at least a substantially non-zero set-back distance before being permitted to join the stream of exhaust gas. Preferably, the exhaust system also includes one or more reverse flow controllers associated with respective cylinders of the internal combustion engine, downstream from the exhaust ports thereof.