I have a 15% pulley. Is it a good idea to spray belt dressing once in a while to avoid slipping? Does anyone have a recommended brand or is it overkill?

 

I'm not sure what the consensus is on belt dressing but if you decide to use it, do so sparingly. I used a bit to try and stop some squealing from my 15% install (w/JCW belt) and found build-up on my idler pulley

 

No way, get the right size belt.

 

Yeah, do that. If I remember correctly, it should be a 60535 belt with a 15% pulley and stock crank. To get it on easier, use a small allen wrench in the tensioner hole to hold the tensioner back. Then route the whole belt save the idler in the middle, when the tension is pulled back more the belt will slide easily over the idler pulley. Surprisingly, it took replacing an old or contaminated belt 4 times for me to figure out this easier way.

 

Belt conditioner will actually shorten the life of your belts.

 

Yup, just like nabeshin said, NAPA 060535 is the correct part number for just a 15% supercharger pulley and stock size crank pulley. Ditch the belt dressing, it's a band aid for a wound that only your wallet can fix. Depending on how old your belt tensioner is, you might want to replace that too. They crap out every 40k miles or so, if not sooner.