12lbs of boost from a JRSC is putting it pretty close to its thermal efficiency limit. If you're going to do that, you'll need some very good tuning, and perhaps run some water injection, since your intake charge is going to be very hot. As for your engine, the internals should be able to handle 12lbs of boost with VERY good tuning, but as soon as you detonate, things can go awry very quickly. 12lbs of boost would probably be the maximum amount you would want to run under ideal conditions, but under real world conditions, you would probably want to run less if you want your engine to continue living. Also, if you have an automatic, the tranny isn't going to be able to cope with 12lbs of boost very well.