in my case, when i had the factory turbo and factory exhaust i got overboost with the tvsv blocked/capped/plugged/etc...
Mike W1996 Toyota Celica ST205 GT-FOURGT2860RS turbine, TiAL mvr44, JE 86.5φ piston, Clutchmasters FX400, APEX P-FC269awhp / 273ft-lbs