You should have stainless steel, mandrel bent 2" pipe if your exhaust is OEM still. All we did on our GV was have a 2" stainless steel Magnaflow muffler put on in place of the stock muffler. Straight through muffler, not terribly loud, nice sound, nice little seat of the pants performance feel. A 4-cyl might not see much difference in power but hey, with the stock restrictive mufflers it can't hurt.
This is all I'm going to do on our XL7 as well. I've spent hundreds of dollars on exhausts and gotten the same seat of the pants feel as I got with just doing what we did to the GV for $130 total.
If your pipe is crusty/rusty/falling apart you might just start looking for a place that can build you what you want.
