There’s a whole lot that makes these mufflers different, starting with the overall design. The bodies start as round 4-inch tubes, then bell out to 4.5-inches, for an aggressive and classic design at the rear. The muffler tip is then rolled to give them a clean, finished look. Internally, these NH mufflers have an 8-inch spun and louvered baffle. This limited louvering produces an aggressive bark.