Best advise i can give is use a dyno but need gauges drive pressure and two boost. You will want to see what the turbos are putting out at full throttle and go from there say the stocker is making 30 and s475 or whatever is making 25 adjust smaller turbo to open sooner. If it was me i would set the stocker to 30psi and let the s400 eat you probably dont have enough fuel to really make a differance.