Hi im tring size the piping for my twin s475's for my 10:1 comp 489" with promax 320 heads. Im looking to make in the 1500hp range with a max rpm of 7500. I have a set of forward turn 2-1/8" primary tube headers to 3" v-band collectors. Heres where some of the questions come in would it be better to use 3"od 16ga exhaust tube or 2.5" schedule 10 stainless pipe from the collectors to the t6 flanges. Next questions is the intercooler charge piping, would 3" od be better or would 3.5 or 4" work better from my 6" thick ata intercooler?

 

KISS. I'd run 3" to the turbos and as big a downpipe as possible. 5" minimum.

You'll be needing to move close to 2000cfm so figure that into your inlet pipe. I'd think you'd want a 4" pipe from IC to carb/TB. 3" from turbos to IC.