Max PSI as in max boost pressure or max PSI as in max cylinder pressure????
If you're talking about max PSI as in boost level, then it depends completely on what type of power adder, intercooler, and cam profile and whatnot. Just an M90 on a basically stock L36, you'd probably only want to run like 5-6psi. Do some valvetrain mods and exhaust mods and unintercooled you could probably pull off like 9-10psi on pump gas. Throw an intercooler on and 13-14psi shouldn't be that hard to do. My setup is making around 13psi right now with an intercooled M90 setup.
However, for your turbo setup, it all depends on what the turbo is, what you are doing for an intercooler, and your cam profile and the rest of your exhaust and whatnot. The bottom end will not give you any problems until you are making A LOT of power. So that shouldn't be the issue as long as you get everything else done right. Head gaskets will start to give you issues somewhere around 18-22psi. If you go with like MLS gaskets and head studs though, you shouldn't have any problems unless you get VERY serious.
Is this some type of a turbo kit you are getting or are you doing it yourself or what?
1990 Maroon Grand Prix STE McLaren 3.1 Intercooled Turbo, 14.695 @ 94.49 on 12psi before cam/heads/etc.
1990 Bright Red Grand Prix McLaren 3.1 Intercooled Turbo, 14.819 @ 92.72, 189whp
1999 Grand Prix GT 9.75:1|K&N|160 tstat|No Ubend/Cat/Res|UD Pulleys|Ported M90/TB/Heads|XPZ|2.55"|Pacesetters|Stage 2 I/C. 12.442 @ 112.78
2000 Blue Bonneville SSEi Supercharged Gutted Airbox|K&N|3.4"|1.9'*|WP Pulley|Custom DHP|180*stat|41932'*|No Cat. 14.681 @ 94.80
2002 Dark Cherry Grand Prix GTP Supercharged & Intercooled
12.084 @ 114.38 w/1.743 60', 315.6whp, Fastest Stock Cam M90 GTP!
NOW XP CAMMED, 340.6whp with XP, stock heads, Gen 3 M90, 11.984 @ 115.84 w/1.750 60'!
Most HP Stock Heads Gen 3 M90 GTP!
2004 Red Monte SS Supercharged K&N|3.4 Pulley|1.9'*|180*stat|41919 plugs|3" dp|No cat/ubend|DHP|Shift Kit. 14.2 @ 98
GOT BOOST??? Friends dont let friends drive stock!