Cant boost past 18psi?

[Rob88]

Its a GVR4 88k miles 20g turbo 880cc injectors comp cams (10200 i think) arp head studs fel pro MLS head gasket ecmlink v3 (SD setup) ETS FMIC FP race manifold ported evo III o2 housing to a 3" DP and an electric cut out. INO MTX WB.

So my problem is i can only make around 18 PSI before the car starts to what sounds like backfire out the exhaust at higher RPMs happens sooner with more boost and is worse if the cutout is open rather then running stock exhaust. if i run it with the cutout closed through the stock exhaust and around 15-16 psi the car runs great.


attached 2 logs. one where it runs fine the other where it breaks up. you'll see im not even running much for timing because im battling knock as well.

 

[bryanwheat]

Check for boost leaks and install a new set of ngk bpr7es plugs gapped to .028

 

[Rob88]

im gonna try taking the gap down and changing the plugs after work. i think i had them gapped at 26 im going to try 20.

ya gapped at 20 it pulls very strong. problem solved!