In my experience with a turbo'ed 250 which have logged 2000 miles or so, your best bet is to use a system like this.

http://www.jegs.com/i/JEGS-Performance-Products/555/52210/10002/-1?parentProductId=924093

I run a fresh air breather on the front of the valve cover and the evac system at the rear. It is plumbed into the exhaust just as it straightens out under the truck.

Basically, the engine is able to inhale fresh air and exhale. The result is no imbalance of pressure.