My glass pack style 4" muffler got old quick. A little too loud cruising and way too loud towing. My ideal muffler would be low restriction, throaty under acceleration, yet quiet when I hit the cruise button. Installed one yesterday that fit the bill. Donaldson #M085171. 8.5" OD with a 35" body. +/- $65. A tight fit, but my muff shop did a good job of jamming it in there. It's a straight through design with a perforated inner core. It has a four section perforated cone in the middle to divert some flow through the outer perforations. Looks to me like it's designed to let you open up the center a little or a lot easily. Custom tune it to whatever noise level you're willing to put up with. I'm happy....kids are peeved. They used to hear me coming a mile away. Now I can sneak up on 'em.