In all honesty i do not know . I was running about 12psi on the std turbo, then we bolted up the hi-flow turbo and would not go past 10psi, but made about 180rwkw (same as std turbo @12psi) As stated b4, we went through ALL other possibilities b4 we decided to try the plugs.
This may not be the case for yourself, just stating what i experienced, hence why i said; "If all tests fail, try replacing your spark plugs."