how does a belt sleep?
what mods are on it that could cause the belt to go nighty night?
LOL^. OP, you mean "belt slip" correct?
What are the mods on the car?
was the belt size changed to account for mods?
you need to give some details if you want help
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Most likely he will need an aux idler and a shorter belt to fit the smaller pulley. Hard to say without detail of the setup (pulley size/belt length).