I had bought some 3" exhaust pipe to replace the exhaust on my truck. I started thinking...and pondering...then I removed the 2 1/2" exhaust on my Liberty and replaced it with a 3" straight pipe. You can really hear the turbo and it seems to spool up better, but it sounds bad. It's too loud and kind of sounds like an old junk car. I'll be putting in a 3" Magnaflow muffler.
Update - I installed the Magnaflow muffler (P/N 12867) I had bought. It got rid of the growl and excessive noise and just left the normal Magnaflow rumble. Unfortunately, it also got rid of the turbo whine I liked, but you can't have everything. This is the final exhaust project. The Magnaflow muffler was small (5" O.D. case, 18" long) and I'm surprised it does as good a job as it does.
Update - The combination of the 3" exhaust, air filter mod, and MAF disconnection has increased my 'everyday' mileage from 19-20 to 23-24. I'd love to see what my pure highway mileage would be. I'd hope 30+.