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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Once the team decided to go all-out and utilize the 10-rib setup, the next step was moving the blower belt-drive in front of the engine accessories. A longer blower snout is used and Steeda designed a bracket support system for it. The support bracket also serves as the mount for the belt tensioner. On the bottom side of the engine, a new balancer is included in the kit. It's a Steeda SFI-certified unit that allows a blower pulley to be bolted on.

Steeda lists the 10-rib drive system as a three-hour installation, but we think it will take a little longer than that, even with an experienced technician on the job. We performed the swap at JPC with the car still strapped down to the chassis dyno; we wanted to do a true A-B comparison. Putting it on the lift would have made our lives easier, but we got the job completed, despite being a little longer than what Steeda estimates. The blower had to be unbolted in order for the snout to be replaced. The Steeda balancer was also a chore to bolt-on since we had to have someone crawl under the car to hold the torque converter in place as the balancer bolt was torqued down. Stock hoods need to have material cutaway in order for the 10-rib pulley to fit under it, which undoubtedly adds time to the installation. Our '07 is equipped with a Steeda cowl hood, so we didn't have to modify it.

"We currently offer three boost levels with a fourth on the way. The lineup will include 11-13, 13-15, 15-17, and 18-21. The final boost pressures are dependant on the engine combination and which generation of Whipple blower is being used," commented Pogel. Whipple has used two generations of rotors inside its blowers; our test vehicle has the Gen II rotors, which generally add 1 or so psi of boost over the Gen I version.

"The advertised boost range would be for a 4.6L displacement with stock internals and exhaust manifolds," said Pogel. "Larger displacements, cams, ported heads, and high flow exhaust all contribute to incrementally reduce boost. The 11-13 kit makes a pretty consistent 12.5 psi on a stock Mustang with a Gen II supercharger. We don't recommend the 15-17 psi kit or the 18-21 kit unless the bottom-end is built with forged components. The 13-15 psi kit is about the limit when using a stock bottom-end. It's mainly for the guys with additional mods looking for 12 psi." We decided to get the 11-13 psi kit due to the stock nature of our engine.

The stock balancer pulley checks in at 6.5-inches while the Whipple blower pulley is 3.5-inches. The Steeda pulleys feature a 2.5-inch upper and a 5-inch lower, which bolts on to the Steeda balancer. Using a calculator, the pulley ratios are different with the Steeda pulleys spinning the supercharger faster (Whipple's 1.85:1 versus Steeda's 2:1). That meant the more aggressive Steeda pulleys would turn the blower faster at a given rpm, resulting in more boost down low and upstairs.

We like the looks of the 10-rib setup and while it is pricey ($1,249 non-polished), the cost isn't bad when you start to break down the kit. We saw a few eight-rib conversions for centrifugal-style superchargers in the $800-$850 range. The Steeda 10-rib setup comes with an SFI-approved balancer, as well as a new snout for the Whipple blower, which other kits didn't include.

On the dyno, Pogel was dead-on with his prediction of 12.5 psi of boost being the consistent output in 100-percent stock applications. The extra 1 psi of boost (over our baseline) pushed power output from 458 to 479 rwhp, a gain of 21 rwhp. On track, the Mustang knocked off a best of 11.49 at 117 mph, while running on a pair of Mickey Thompson 275/40-17 ET Street Radials.

The power output at 479 rwhp is about as far as you'll want to go with the stock automatic transmission and stock Three-Valve modular engine. That level of horsepower has proven to be reliable in many other '05-newer Stangs so we aren't worried about breaking anything. While Steeda offers higher boost levels, we will just enjoy our mid-11-second ride for now.

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