An exhaust system for an internal combustion engine having two banks of cylinders by which pulses of exhaust gas are alternately directed to a diverter subassembly. The diverter subassembly, which is located in the muffler, includes a perforated gas decelerator chamber which divides each pulse of exhaust gas between two exhaust outlets and causes a low pressure wave to occur in the exhaust system to enhance scavenging of a subsequent pulse of exhaust gas and thereby improve engine performance and mileage. The muffler further includes one or more cores and may or may not include a dead air space chamber to provide attenuation and tonal balance to the exiting exhaust gas.