Abstract: An exhaust back pressure reducer for use with an air deflector on top of the cab of a tractor for deflecting air over the tractor as the tractor pulls the trailer over the road. The back pressure reducer generally comprises a device at the top of the air deflector on the cab for aspirating exhaust gas from the engine exhaust system to reduce the exhaust back pressure on the engine. The aspirating device is positioned for flow therepast of air relative to the air deflector as the tractor travels forward and ported for suctioning gas therefrom by the air flowing therepast. The exhaust back pressure reducer further includes a connection between the engine exhaust system and the aspirating device for aspiration of exhaust gas from the exhaust system as the tractor travels forward over the road with attendant relative flow of air up and back over the air deflector and the aspirating device on top of the cab.