ok I know to go steel on the downpipe and aluminum on the intake pipes

but what size?

Throttle body is 70mm
Turbo intake is 2 inch
turbo output is 1.5 inch
ic in/out is 2 inch
Maf is 75mm

My problem is that I dont want to have to redo the piping, and I'm upgrading to a gt2871r later on (probally before summer to be honest)

I was thinking of going :
filter to turbo 3 inch (bottleneck it with a coupling)
turbo to IC to TB 2.5 , and bottle neck it was well with couplings


I'll boost 5lbs with the turbo I have now, and with the new turbo I'll boost 15-20 (after engine is built of coarse)

opinions please.

How much HP are you planning on running with the turbo. In my humble but accurate opinion, 3 inch exhaust's are only helpful at 300hp and above. Anything less is simply over kill.

225 to start, working my way up to 300+ hp , 300 with turbo, and then a shot of nitrous.

I have 3 inch for the downpipe

Then deffinately stick with the 3. You won't need it at first but do it for the future. Intercooler piping is a good size. Don't change that either.