The large spring inside the clutch boss "acts" as a tensioner. you can check it by grabing the pulley in both hands, it should take considerable force to move it out. The stock belt can tear the filaments that bind it together, causing a stretch, you should be able to spot this by torquing the belt sideways, all along the length. you will find a soft spot that will flex more than the rest. If you have to replace the belt I would stay w/ the stock #'s, as long as you have the rest of the tranny parts stock. The reason is, most of the kevlar replacements are made to match their own components, meaning slightly different fit.