Abstract: An apparatus which is adapted to be retrofit onto a tailpipe of an internal combustion engine co-operates with the primary emissions control system of the engine to improve the overall performance of such control system. The apparatus includes a housing having an inlet connected to the tailpipe of the engine, and an exhaust gas treatment device in fluid communication with such inlet. Overall fluid pressure drop in the system is controlled by a fan which is powered by a motor mounted on the housing. The motor is powered by the engine, and is controlled according to pressure in the exhaust manifold of the engine. The exhaust treatment apparatus can include various elements, such as baffles, charcoal or particulate material.