Surely its whatevers MOST restrictive?

Most the time its the turbo exhaust housing, but could be head, cams, manifolds, exhaust, anything.

But IMO once the most restrictive thing is made less restrictive then you got more airflow at the same boost level, so need more fueling.

Remember when Stu said about they needed to remove 10% or somthing of the fueling on Seans car when they went back to a mongoose from the 4" bore drainpipe he was running.

This is another "need Stu or Karl to confirm/explain properly" type post, as its hard to put into words.