Michael Galimi
December 10, 2009

One of the tried and true bolt-on items these days is a supercharger, especially in the mod motor market. A supercharger adds more horsepower by stuffing the engine with more air, which when mixed with more fuel-and the proper spark-leads to a severe increase in horsepower.

The '05-newer Mustang market benefits from 10 different companies offering a wide assortment of supercharger systems that help provide a mild or wicked punch. Each system and style has its own merits, and they all share the simple notion of using a belt to drive the supercharger. Therein lies a potential problem-belt slippage. If the belt slips, then the blower speed will slow, thus leading to less boost, and ultimately, less horsepower.

Over the years, we have seen some crafty fixes and bandages to keep the blower belt from slipping away and decreasing precious boost. Increased belt tension helps, but the most effective technique we have seen has been through larger belt contact on the pulleys. A surefire way to get more contact area is to run a wider belt. The stock serpentine belt for any year modern Mustang has six ribs (excluding factory supercharged Stangs). Most blower companies today utilize the six-rib configuration, as it is usually very durable when the blower is installed out of the box. But just one taste of boost usually has the owner begging for more-and that's only a pulley change away.

That was our problem when we slapped a Ford Racing/Whipple H.O. kit onto a '07 Mustang GT (equipped with an automatic). Before the supercharger installation, our test Stang benefited from a modified tune and a Ford Racing cold-air kit. This was our baseline trim, and the Three-Valve produced 265 rwhp. Once the blower was installed, the gang at JPC Racing strapped it to the dyno for more tuning and final horsepower results. We expected the numbers to be fairly decent since the supercharger has Whipple's Gen II rotor internals. Our suspicion was correct-the car made 459 rwhp with the out-of-the-box kit and a custom tune in the computer (which was uploaded using the new DiabloSport Trinity programmer).

JPC's Justin Burcham logged the boost using an input on the dyno and saw it peak at 11.5 psi at 6,400 rpm-right where the power began to fall off. Instantly, we interrogated Burcham about getting a smaller blower pulley for a little more boost. After all, if a little is good, then more is better! Fuel supply wasn't an issue with this car, as we had previously installed a Lethal/Fore Precision Works billet fuel hat with twin Ford GT pumps, a Zone 5 FPDM, and a set of Ford Racing's Shelby GT500 47-lb/hr fuel injectors (PN M-9593-G302). Our hopes for more boost with the pulley swap, however, were dashed.

"For the most part, the kit works great out of the box. But I have seen the six-rib setup shear or break belts once the blower speed is increased. The life expectancy of the belt lessens," said Burcham. He isn't the only one who has experienced these problems firsthand, "Put simply, we were tired of breaking belts. We were breaking belts on the street, and on the strip-even with moderate shifting."

"After discussing it with our trusted partners, we found we were not alone, so we decided to do something about it," commented Aric Pogel, design engineer at Steeda Autosports. The Steeda solution was a dedicated drive system that was tested and flogged on several of Steeda's sponsored race cars and in-house Mustangs before it was approved for sale. Pogel did admit to being vague when answering some of our questions because of some tricks and special engineering that went into the design.

The Ford Racing blower pulley is mounted inline with the factory accessories-a longer belt is used to incorporate the blower pulley in the normal operating order. One would think an easy fix is just replacing all the six-rib pulleys with eight-rib pulleys, but according to Pogel, it isn't that simple. "Our first step was to do just that; we ran eight-rib truck pulleys. It helped a little but we still found ourselves limping back to the pits on Whipple's air bypass. With further testing, we discovered the root of the problem," he commented.

Pogel wouldn't give us the source of the belt problem, but it is obvious to us that it had something to do with running all of the accessories inline with the supercharger. The final solution was creating a dedicated 10-rib belt-drive system solely for the supercharger. "The next challenge was a matter of packaging it under the hood," he continued. "We determined an eight-rib pulley didn't offer any packaging benefits. Both belt sizes cleared our hood (Steeda S197 cowl hood) and both required modifications to the stock hood-the only difference between the belts is 7 mm."

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