i want to go FMIC. in the future (year or so) i want to upgrade turbo and shoot for 400-450 rwhp. how much of a difference will i notice with 3" verses 2.5" piping on stock turbo? if its a huge difference ill just go 2.5 now and upgrade everything to 3 when i go to a big turbo. if its not THAT big of a difference ill just go 3 " now and bear with it for a year. what are the downfalls of the 3" compared to 2.5" with stock turbo? ive been reading and searching for an hour, and havent found my complete answer.

increase in lag...how many RPM higher? (medium streetport, FULL straight exhaust)
anything else?

 

The biggest thing you need to worry about is boost creep. I've got an s5 turbo with 3 inch downpipe and some kind of ported wastegate (I didn't do it and I haven't looked at how extensively it was ported) and I will still spike 14psi in higher gears and that's runnning with no boost controller.

If you run the bigger downpipe, make sure you've got a solid wastegate port.

 

i was talking about 3" intercooler piping. i have a haltech so no worries about creeping, as i will be running 12 psi most of the time and it will be tuned for about 15 to whatever it bleeds off to.

 

short answer.

2.5". you wont be needing 3". period.

the stock piping is just under 2" IIRC. The volumetrics of the 3" piping is not a good idea unless your talking something in the T88 range. And even then there is some fluid flow characteristics to consider.

 

^^i agree i have 2.5" and that seems to be fine.

 

on a stock turbo, you will be running whatever boost your wastegate will let you run. There's a reason why people do monster ports on the wastegates, remember that.

 

thanks guys! i was probably going to go with aspec gt35r (t4) kit