The kit I bought was 2-1/2" all the way with smooth mandrel bends. It's aluminized not stainless but neither is the factory cat-back and at least the Dynomax kit has a nice S/S tip with logo laser etched into it which finishes it off nicely. . . oh, and did I mention it was only about $175 delivered to my door from Summit. (Granted, I was looking at the Gibson and Magnaflow systems which are great systems and all S/S. They probably sound better but not 3 times the price better). You get what you pay for. If I had $500-$600 to burn I'd have gotten the Gibson or Magnaflow but that is out of my family's (kids with braces) budget.