i think i got it all figured out. Thats some great info also found some other stuff here is a great link from DSM guys.
https://www.youtube.com/watch?v=nhYlXr-tHpY
My goal 400whp but ill take more
fully built bottom end 8.37 compression rebuilt head with hks 256 cams.
turbo gen 2 gtx2867 flows 30-40 lb/min
@400whp i need pipe capable to flow 570.80 cfm which comes up to a 2.25" pipe if my math is correct.
But i will sacrifice some lag and go with 2.5" hot side and 2.75 cold side just to give my self some room for larger turbo down the road.