At 16psi you should be around 320 minimum, i tune 93octane an see this regularly with very little work and stock cams. The stock cams usually bang out around 330-335 when boost is turned up to 17-17.5psi, running the 2871r, 555cc or larger and z32mafs. I know that with just an intake cam(256) you can hit 350. I know some new enthusiast choose for me to tune this setup, because the vacuum is still strong with the stock exhaust cam.
It's now my recommendation for 350-370 power range. After a year or so, you'll be wanting more anyway.
My bad you have the gt28r compressor housing, never really pushed that housing on a 2871r, so maybe it flows like the gt28r? if that's the case you are actually right were you should be.
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