Corky Bell's _Maximum Boost_ is an excellent primer on turbocharging. Required reading if you're thinking about modifying your existing system.

If I recall correctly, his advice is to raise the boost to compensate for the pressure drop caused by the intercooler. This would also require an accompanying increase in fuel delivery to take advantage of the added boost pressure. So, the intercooler will allow you to operate with more boost safely, but you will need to re-tune the engine to take advantage of it.

1988 Isuzu Trooper LS
2.8l Isuzu 4JB1-TC intercooled turbo diesel
www.dieseltrooper.blogspot.com