18 PSI where in the powerband? With an 18g on a 2.5L, adding boost only typically yields more torque through the powerband, as your tune is typically limited by the turbo up top (which is where you make peak HP). If you want to add HP, you will likely have to add some e85, meth, racegas, or some better breathing parts. To be perfectly honest, your numbers sound very low for that type of set up. I would expect ~280 WHP on a mustang dyno and ~300-310 WHP on a dynojet. What size 18g are you running?