the turbo is too small.. I have owned 3 turbo subarus all 2002 or newer. I have done all my own motor work for over 10 years on high hp 4 bangers.
the turbo is working too hard and there is no intercooler. look into turbonetics, or blouch. and maby look into how the mr2 dose there intercooler. and i would swap out to a stand alone ems. I use aem in all my tuned turbos
I understand you are using water injection witch I have used and love, but never with out a intercooler.