95RedEX

I did that on my first IC setup. I had 2" from turbo to DSM SideMount and then a 2" to 2-1/2" reducer right after the IC to go to the throttle body, which is 2-1/2". Worked good.

I added a CCA FMIC over the winter and changed all my pipes to 2-1/2", since my TB is 2-1/2" & my IC inlet & outlet are also 2-1/2"... So I have a 2" to 2-1/2" reducer right off the turbo and 2-1/2" piping throughout... I'm still undecided as to whether or not that was the right decision.

FooK

smaller 2" piping is great for spoolin it up, but i prefer a little lag and better top end.

dyno proven 2" to 2.5" conversion on Alec's ZC was something like 14whp. I think the before dyno was 185whp and the after dyno was 198whp.

Threads

I just did the same size as my cooler. 2.5". But my compressor outlet is 2.25". I get a bit of lag, but I rather a bit more top-end.