I just recently started buying stuff for my turbo project and wanted to know something. If i get a 2.5inch downpipe with a 3 inch exhaust would it effect performance or would if be alright.

 

2.5 is more than enough for under 10lb of boost for sub 2 liter 4banger

i was running 2.5 all the way with test pipe and no resonator

 

Agreed, 2.5 / 3.0 diameter pipes are more than sufficient for what you need. It MIGHT run a little "flat" until the turbo spins up (lack of exhaust scavenging from over-sized pipes) at which point you won't care

P