Trying to finalize my turbo charge pipe situation, its currently 16.4ft 2" and 4ft 3" pipe, if that dosent sound efficient its because its not. I need to figure out what sizes to use and I’m not sure how velocity figures in. Ideas are appreciated.

Two 2" pipes totaling 16.4ft Y’ing into 4ft of 3" pipe that connects to the throttle body.(rough measurements) The total volume is 957in cubed. I want to replace the hokey flexible ducting with steel and while I’m at it make it spool faster (without choking the motor).

On the dyno in 5th gear the car made at least 1psi from 2000 and that climbed until about 3600 where the turbo began to really spool, Peaking 7psi at 4400.

I want to connect the two turbos earlier and run a single charge pipe through the car, so it would be about 3-4ft 2" pipe then 8-10ft of 2.25, 2.5, 2.75, or 3" pipe. I don’t know what size to pick.


Due to the turbos sitting so far back the exhaust gasses cool and the turbos are less efficient, so the motor runs at atmospheric pressure until about 3500rpm.(depending on gear) I’m afraid if I choke the motor by using a charge pipe that’s too small it will take even longer to spool. I just can’t imagine a 4.0 v8 being happy pulling air through a 2.5” straw, but on the other hand it seems unlikely that you’d pressurized 10ft of 3" and still have good pressure.

What calculations should I be doing? How does velocity and Cfm play into all this? Any ideas