I recently purchased a 4" exhaust from Rip Rook. It uses aluminized steel is mandrell bent and has an Allied H/D truck performance muffler. Plus the price was reasonable. I havent installed it yet but I have heard it on other trucks and it sounds great. He is in the Portland,Or area. NW Bombers it would be worth checking out. Makes it nice to have a local installer as well. Oo. Oo.