GrahamF

Just serviced by MY98 (ITG+T75 downpipe + phase 1 ecu), cleaned out all the vacuum pipes and fitted a boost gauge. Initially max boost was 15/16 psi which I guess is standard, but then I switched to SUL. Now boost peaks and hold 20psi, and occasionally the overboost just kicks in if I boot it really hard. Feels great, but the question is, is this too much boost, and if so, how do I get it to a reasonable level? I know it should have a better exhaust system (currently standard from the downpipe back), but would that raise or lower the peak boost?

Graham

john banks

15/16 PSI would be high but understandable and quite sensible with a remapped ECU (PE Phase 1?), and 20PSI is rocket ship and possible bang bang time - STi engines run 17 IIRC!

My MY00 PPP was hitting 20PSI peak and 16.5PSI held - but boost was fluctuating all over the place! Now hits up to 18 peak (usually 17) holds 16.5PSI and this is about the best the PPP ECU will tolerate.

You could
1) go back to UL
2) get remapped to whatever fuel you are going to use
3) consider if you can change the size of the restrictor from the manifold to the wastegate actuator to slow the spool up/reduce peak/held boost (which does not go higher than the peak).

Best speak to whoever did the Phase 1 remap.

Whatever, 20PSI sounds too high to me to be running unless you know you are not detting and you trust Subaru's chocolate internals with that much. Better exhaust will only make the problem worse - but not horrendously so as you have already removed the factory DP which is the biggest restriction.

Would advise driving on light throttle and keeping the boost well below 16PSI until you know it is not knocking.