Pressure ratio on the compressor maps refers to the ratio of boost+atmosphere over atmosphere. so 1.0 on the map is ambient air pressure 14.7 + 0/14.7 or 1.0
so in terms of boost pressure:
1.0 = 0psi
1.5 = 7.3psi
2.0 = 14.7psi
2.5 = 22.0psi
3.0 = 29.3psi
etc
So if the 88mm pulley produces 11-12 PSI, you are at 1.5 to 2.0 Pressure Ratio, so for the c38-81 you are in the middle of the Compressor map just below the 70k line.
On the c38-91/92 compressor map you are at a similar spot but by the looks of it, the c38-91/92 compressor actually has a lower top spinning rate where the 81 can go a bit farther.
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