Straight-through flow path. Exclusive expansion chamber dissipates annoying mid-range drone. Flows up to 201% better than stock. Authoritative, but never overpowering, exhaust sound. Polished-stainless steel. 4 inch diameter in/out.Monster Exhaust Benefits. Replacing the restrictive stock muffler with Banks free-flowing Monster muffler makes a huge difference in airflow, sound, and performance. The Banks muffler has a large inlet and outlet where the exhaust flows straight through, compared to the torturous stock design with hairpin chambers that build up back-pressure. Only Banks Monster Muffler has an expansion chamber to alleviate the nasty drone that other straight-through mufflers are known for. Banks utilizes durable ceramic packing with a high temp rating so it won't degrade like fiberglass. Add it all together and you get a muffler that flows over three times better than stock and delivers a pleasing, throaty rumble!