^+1. At your power level you should NOT be breaking tensioners. Something else is not set properly or the belt is too short.

 

I thought the belt was too short because even with the tension arm all the way down, it barely clears the alternator pulley. i bought the next size up but it was too long and slipped off the pulley and shredded. But some very good reliable mechanics assured me that my belt wasn't too short and so did Scott who does the mosaleen idler pulleys. He said on a 99 that i should be running a 118.26 inch gatorback and thats what i have. I think the torque from my modified 4r70w is what snaps it. My shift pressure is higher than you can make a stock tranny perform. I can't control it though because the pressure comes from the vacuum line from the SC. It performs great at high speeds and outperforms a manual everytime. Its the transgo stage III shift kit and it puts a lot of torque on my belt when i shift (car jumps like it has 500 rwhp when i shift). Even with radials and a good burnout i always chirp my tires from 1-2 and i know its because of the tranny because it did that before SC'ing it.

 

Check to see where you are on length for the belt. With the belt on, note position of the tensioner. Then release the belt and note the position of the unloaded tensioner. You then note the travel of the tensioner fully loaded by applying tension with a wrench to max postion loaded. You should be close to the middle of total travel with the belt on. Check pulley alignment too.

 

its not in the middle like it should be but they don't make a belt thats a 1/4 - 1/2 inch longer. Though when i swap my SCer pulley for the smaller one, it should give me a 1/4 inch of slack.