I have been having problems with my belt slipping ever since I installed underdrive pulleys. It would always slip when I would start the engine (cold or hot) and during hard shifts. I tried various belt lengths, new tensioner, belt dressing, different brands of belts, even went to a less powerful alternator (300 --> 200 amp = lighter)... nothing worked.
I figured that the problem was with the alternator pulley contact area, since I swapped alternators temporarily with a slightly bigger pulley and the problem went away. However I needed the small pulley to charge at idle.
So I relocated the idler pulley using one of the alternator mounting bolt locations. The belt needed with march underdirve pulleys is 94" (940k6). As you can see, it now has close to 180* wrap on the undersized alternator pulley. So far, all is good
The wrap on the A/C is a little less than it once was, but that has not slipped yet. There is a spot under the compressor where an additional smooth idler pulley could be mounted if necessary.
I hope this info helps someone. It took me way too long to figure it out.
