was wondering what size tubing i should run from the IC to the TB. i have a 90mm tb already. my IC has 3" outlet. combo is 408 with a PT88. should it be 3" to the TB then step up right before the TB, should it be 4" from the IC to the TB with stepping it up at the IC

 

It would seem crazy to run a 90mm TB, then feed it with plumbing that is much much smaller.

You could solve that 2 ways.

 

i am using 3" from the turbo to the IC, then the outlet of the IC is 4" were i take a 4" pipe to the throttle body with no maf.