I'm thinking that my blower is not boosting as I only get about 2lbs of boost on my gauge. I checked the tension on the belt but don't know if the pulley is attached to a tensioner, the belt goes around the cranckshaft, a pulley and then the blower. I only found 1 bolt on the pulley but if I turn it left it loosens the bolt, if I rotate it to the right it tightens the bolt and does not take the tension off the belt. I guess this post is confusing with out pics, but i'm hoping some one may know what I'm talking about.

the car is a 94 z28, with a vortech blower.

 

The tensioner has a black pulley for the back of the belt and a silver spring housing which is the pivot point. The belt bends around it on the right to give you more pulley wrap as you look at it from the front of the car. It is usually very tight - obviously the tensioner can't be at the end of it's travel with the belt in place or there would be no tension.

Also check to see if your bypass valve is working - maybe pull it off and test it with a mityvac or something or you could try pulling off the hose while it is running and see if it closes - it should sound differently if it does.