belt slip

Reducing belt slip can gain additional boost with a given blower pulley setup. As well stated by Magnum Powers:

"Supercharger belt slippage can reduce power so a few issues need to be looked at. First you should only use good quality belts that are in good condition, we recommend Gates Green Strip belts. If you see boost levels falling off you might consider an aftermarket idler pulley that creates addition belt wrap around the blower pulley. Several are on the market including one manufactured by Magnum Powers that is adjustable so you can run various size blower pulleys and still have maximum wrap angle around the pulley. Also run the shortest belt possible so the belt tensioner is exerting maximum force on the belt."

Don't mess with the upper pulley: The best way to prevent belt slip is to never reduce the upper pulley size. There is just no sense in it. Reducing the pulley size reduces belt grip surface area. The stock upper pulley is too small as it is. All boost increases should be made with crank pulleys. If you run out of lower pulley options (i.e., want more than 8 pounds), you should upgrade the blower. An 8 pound pulley is stupid big for the stock Eaton without dramatically reducing the rev limiter and shift points.

Don't use Gatorback belts: Many have reported that the Gatorback belts increase belt slip and have gained back boost when switching back to a plain ribbed belt.

Idlers: Extra idler pulleys can be used to provide more wrap around the upper pulley. Metco makes the original extra idler kit. It also sells larger idlers for the stock two locations. Pulley alone $50, complete assembly (less required extra idler) $200.

Magnum Powers makes a neat idler kit ($260) that replaces the entire lower brace and has the extra pulley on the other side of the belt, which Magnum asserts is where it should be. Magnum claims 7-30 rwHP, depending on how much belt slip exists before installation.

The below image shows how well the Magnum brace wraps the upper pulley. I like the fact that the Magnum kit uses the stock Ford idlers -- several have reported bearing failures with aftermarket idlers.

Reichard Racing upper pulleys: The Reichard Racing upper pulley ($130) has slots cut in the pulley to grab the belt. It is reported to shred Gatorback belts quickly, so a plain ribbed belt is required. It is offered in stock and smaller sizes. As stated above, though, there is no sense in reducing the upper pulley size.

Reichard claims large power gains at higher boost levels.

The bottom line: The most cost-effective and hassle-free combination to reduce belt slip seems to be the Magnum Powers or LFP extra idler kit with the right length Gates belt. Spend the money for bling bling billet idlers or $25 for an OEM one. You make the call.