Paxton's New Eight-Rib Belt-Drive System - The Driving Force

Belt-driven boost-makers, better known as superchargers, go with Mustang performance like hot dogs and baseball. The popularity of supercharging is evident by the sheer numbers of systems and configurations, especially those for the '11-present Mustang GT and Boss 302. Last we counted, there was no less than eight manufacturers offering varying levels of superchargers for that genre of Mustang. And there are even more kits for the Three-Valve.

The Coyote 5.0L responds well to boost, as we've documented on these pages and in the virtual world on the magazine's website. We've watched the Paxton kit help a Coyote produce over 600 rwhp with minimal aftermarket upgrades. Turning up the boost has also become a time-honored tradition when out-of-the-box boost just doesn't quite cut it. And a simple swap in blower pulley is usually all that's required to accomplish such a task.

A supercharger is driven by the crankshaft and for most applications a serpentine belt connects the crank to the supercharger. There are exceptions like race-only, cog-belt-drive systems and gear-drive setups, but those are rare for street machines. For those who purchased a Paxton supercharger system for the Coyote, the supercharger is driven with a six-rib belt system that is run inline with the factory serpentine-belt-drive setup.

A series of idlers and tensioners keep tension on the belt, thus providing traction on the pulley. The six-rib configuration works well for the average installation, and also in cases where a slightly smaller (than stock) supercharger pulley has been added. The smaller supercharger pulley increases supercharger impeller speed, which creates more manifold boost, but it also provides less area for the belt to grip and drive the blower. The byproduct of more boost is increased output--provided your fuel system and drivetrain are up to snuff. Moving past the higher boost concerns of tuning and durability, there is one issue that can rear its ugly head: belt-slippage.

As the impeller speeds up, there is more load placed on the drive system, and that can lead to slip. Paxton recently released an upgrade kit to convert the six-rib pulley system on the front of the Coyote engine to an eight-rib combination, which offers more area for the belt to grip. The kit retails for around $650 and has all the necessary pulleys, idlers, spacers, bolts, and washers. The installation is rather easy, and the two biggest steps are removing the supercharger head unit and brackets, along with installing a new crank pulley. It sounds complicated, but the swap is relatively simple--especially if you installed the system yourself.

The extra two ribs of surface area might sound like a small increase, but it's a significant one as the width goes from 0.82 inches to 1.10 inches, making the eight-rib belt 34-percent wider than the six-rib. We had one car in mind to properly test the eight-rib belt upgrade and it was the in-house mule at JPC Racing, which belongs to the shop's owner Justin Burcham.

We figured if we were going to torture test a belt-drive system then this car--and owner--was our candidate. It represents the highest rwhp rating of any Paxton-equipped Coyote 5.0L and is one of the more prolific Coyote performers, with a best of 9.34 at 150 mph on the drag strip.

The 2011 Mustang features a stronger RGR bottom-end with mildly ported heads (stock valves and valvesprings), valvespring shims for more seat pressure, OEM camshafts, and a stock intake manifold. A JPC Racing return-style fuel system ensures the engine is fed plenty of Shell URT fuel while the final touch for fuel involves a set of Injector Dynamics ID1000 fuel injectors. The exhaust system is all JPC Racing from the headers to the mufflers. A Paxton NOVI 2200 head unit is included in the company's High Output tuner kit. JPC Racing converted the kit to a blow-through MAF sensor setup.

The car made 843 rwhp with the six-rib serpentine belt, and boost peaked at 15 psi. It's an impressive number, but the boost data-logger on the chassis dyno showed the manifold pressure fluttering in the upper rpm range and power starting to fall off. The Paxton NOVI 2200 supercharger hits 15 psi by 6,200 rpm, and more or less remains around 15 psi through 6,600 rpm. After that point, the boost steadily decreases to just 13.5 psi by the 7,200-rpm redline. The power fell off as the boost dropped, as evidenced by the 6,600-rpm peak-rwhp rating. As mentioned before, we chose this car due to its extreme nature as Burcham has a 3.10-inch upper pulley on the supercharger. Its small size means less surface area and less belt traction.

We installed a 2.85-inch blower pulley after adding the eight-rib pulley kit. Astute readers will note that it isn't the same as the baseline six-rib supercharger pulley size. Our goal is to push the limits of the eight-rib drive system so spinning the blower harder would help reveal its effectiveness. The crank pulley remains the same as the out-of-the-box Paxton six-rib crank pulley--at 6.65 inches.

Once on the dyno, a few easy warm-up pulls were made and all systems were inspected. Once Burcham had the all-clear from his guys, he fired up the car, shifted his way into Fourth gear, and went wide open. The 7,200-rpm redline came quickly and all of us scrambled to get in front of the computer. Boost shot up to 19 psi and output increased to a staggering 996 rwhp! The boost curve was smooth from start to finish, showing the eight-rib drive certainly helped belt traction.

Naturally, we couldn't leave the car alone since the magical 1,000 rwhp was just a pulley change away. The lure of peer pressure is too great when you're in a room full of gearheads and only 4 rwhp shy of a significant accomplishment.

Paxton, however, cautioned Burcham that his supercharger is at its 60,000-rpm efficiency range with the 2.85-inch pulley. But if there is one thing we know, it's that the limit can be pushed a little more than advertised. Burcham grabbed a 2.75-inch, eight-rib pulley that was treated with Carbonite, which is a rough coating used to promote belt traction. If the belt held, then we knew the smaller-diameter pulley would be worth at least 1 psi of boost.

Burcham warmed the car up as he went through the gears in the Tremec Five-speed transmission. He got into Fourth and then went right to the floor. The car strained, screamed, and hummed its way to 7,200 rpm. We crowded around the computer monitor and to our enjoyment it read 1,032 rwhp and boost peaked at 20.5 psi.

At the time of the writing, the JPC Racing testbed recorded the highest rwhp of any Coyote 5.0L--street or strip--and it did so with stock camshafts, mildly ported heads, and a better rotating assembly. Most importantly, the eight-rib drive system performed nicely as the boost curve had a smooth ramp right up to its peak boost of 20.5 psi. A few backup pulls showed the 20.5-psi max was dead on. We spun the NOVI 2200 to 62,679 rpm and the boost held rock solid through 7,200 engine rpm. Putting an eight-rib pulley system through this extreme case is certainly proves its effectiveness for milder combinations.