sounds like something geo could answer lol
but if it were me i'd wait to get the turbo first then build a custom exhaust at the same time, because if i decide to throw on a 3" exhaust now w/o turbo, i'd probably lose a hella hp on the low end but maybe gain very little on the top, i remember in my old sentra i had a 2.5 in crush bent exhaust (yeah, i know) but it help a lot when i was spraying lol but just cuising around town kinda sucked cause i had no kick off the line, their was probably zero back pressure, so i'd just wait and see if you really end up turboing, which i don't have a doubt, and then decide from their, so anyways good luck :alien: