There may be two things going on here.

1. Proper tightening
2. Proper pulley

1. To correctly tighten the pulley it is necessary to adjust the tensioner bolt correctly with the adjusting screw and then climb under the car and tighten the pulley nut to lock it. Failure to do this will cause extreme wear on the mounting plate and parts. This result in unusable or broken parts and belts shredding and comming off.

2. The Vortech factory pulley and the ones by some other manufacturers have no lip. Engine torque causes the belt to skip and possibly jump off the pulley. Running over one notch is enough to destroy the belt. This is why I recommend the ASP pulley. Kane sells them but I can't find his information. http://www.aspracing.com/frame.htm

It has a nice lip and the belt can not jump over when properly tensioned.



The black pulley is a factory Vortech and the one on the right is ASP. Notice the lip on the ASP. No jumping problems there.

Another picture of the ASP pulley.


Also as others have stated make sure the pulley is on the supercharger in the correct orientation.

Good luck.