help with belts coming off

hey I have a mustang with a 306 head,cam,intake,novi 1000 with a 8 inch renegade crank pulley,(only pushing about 7 lbs of boost) stock supercharger pulley on it.. two belt system..my problem is ,when ever i launch it real hard both of my belts come off. i have replaced the harmonic balancer with a stock replacement..and it stopped for awhile.how do you check to see if every thing is straight for alignment? i really dont have any problems with street tires but when i use sticky tires or slicks it seems it always throws the belts..like we just made two passes tonite left foot braking it about 2600 with no problems then left off transbrake at 3000 to 3200 and about just before the 660 the belts came off..any suggestions? anybody else had these problems with the two belt setup? real frustrating because i was gonna try to hit a 11 flat or even crack into the tens tonite...oh well

I had to shim my tensioner and the water pump pulley. Even a little bit will throw when you lanch hard

was this for a single belt setup? i am not sure which belt is thrown off first,all i know is both belts are off but the supercharger belt is usually destroyed. this time i only had had half of the belt left..turned into a 4 rib belt..