can't keep belt on my 454, engine throws them under full throtle runs. gave up on original put on gilmer pulleys and new power steering pulley, one run rolled power steering belt and chewed up edge of gilmer. is it possible that the thrust bearings allows crank to move enough to cause that much mis alingment of belts. seems to be a good 1/8"+. car runs good no noises just the belt problem. only thing i can come up with is thrust bearing.

How about pulley alignment. Both pulleys need to be in the same plane and the belt should enter/leave the pulley straight. Look from the side; sight down the belt; if you see any mis-alignment or kink, the belt may stay on fine thru normal throttle, but it will jump at WOT.

The best way is to put a straight edge on the face of one pulley and extend it across the face of the other one. Since you can't get an actual metal yardstick to fit there, try a Laser. Either a Laser pointer, or one of those construction lasers, used to level pictures etc. You should be able to see any mis-alignment.

I started throwing belts last season, and traced it down to my power steering pump, which had two bolts loosen up on the back/side bracket
and this cocked the pully quite a bit.

Good Luck

Just make sure you use a good belt too. I've had a cheap Autozone belt fly off when I was under the hood revving the motor. It looked like a rubber band expanding and then flying off. HEEE!!!