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That depends on what you drive. Go to your profile and fill out your signature with the year, model, options, and whatever mods you have so far.....makes it easier to answer your questions.
Pulley alone is ok, but works much better with a custom intake. You have to ALLOW the air your blower is demanding. For Series 1, 92-95 with the pulley and intake alone, I think 12 pounds total boost is reasonable. Other mods may take you higher, exhaust will lower your effective boost if done incorrectly.
For Series2 from 1996 to present, I believe 13 is possible with just the pulley and intake, but 14 to 15 wouldn't be out of the question with other mods. Just off the top of my head. There are some differences between the 2 series. Go to the Techinfo link up above. In the Specifications section you'll find the M62 and M90 Eaton specs, and in Tech Know-how, you'll find some other pulley/sc/intake articles. Keep in mind there are several pulley diamter options available for all these years. Some are more practical than others, but for the most part, with no other mods, one step down in diameter is best.