Originally Posted by TBatt

The main serp belt is a 7 rib. Stillen supplies a seven rib in their kit that works for the stock setup. On the SC mounting bracket, Stillen includes a threaded hole for an additional pulley to help with the belt wrap around the jackshaft drive pulley. The only belt, that I could find, that was the proper length is an eight rib belt. That is the belt I went with and simply cut off one of the ribs.

On the SC side we have an eight rib belt. If you use a 2.9 inch SC drive pulley you will not have enough adjustment of the idler pulley to prevent belt slip. What we have done is to replace the SC side idler pulley with a larger diameter idler which takes up more of the slack and allows you to get proper belt tension. As an added bonus the larger idler allows for more belt wrap around both the jackshaft and SC pulleys.

For more info check this out: New FI club member