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.
6 In addition to the Paxton...
6 In addition to the Paxton idlers and pulleys, there are a few OEM pulleys that are replaced, like the one on the alternator.
7 The water pump pulley is...
7 The water pump pulley is also converted to an eight-rib-style.
8 Paxton supplied the lower...
8 Paxton supplied the lower crank pulley and it was the identical 6.65-inches as the six-rib one we removed. The outer pulley (top) is for the power steering pump, while the inside section (bottom) is used for the serpentine system. It is the inside section that measures 6.65 inches and effects supercharged impeller speed. A larger-diameter pulley will spin the blower harder, while a smaller-diameter pulley will slow it down.
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.
9 Here is a comparison of...
9 Here is a comparison of the six-rib supercharger pulley (left) and the eight-rib pulley (right). The six-rib is 0.82-inches wide; the other features a width of 1.10 inches.
10 We went with the 2.85-inch...
10 We went with the 2.85-inch pulley because that was the smallest one Paxton offers. The reason behind the small pulley was an attempt to slip the belt. It didn't work.
11 The supercharger pulley...
11 The supercharger pulley slides on to the shaft and uses a keyway like a crankshaft/balancer setup.
12 The bolt is hit with the...
12 The bolt is hit with the impact gun. We're sure there is a toque spec somewhere but we didn't bother to look it up. This is how most of us have changed centrifugal blower pulleys over the past 20 or so years.
13 Paxton includes spacers...
13 Paxton includes spacers of varying sizes from this short one to taller ones. These are used to space out the Paxton supercharger-mounting bracket to fit the thicker pulleys and belt.
14 The mounting bracket is...
14 The mounting bracket is reinstalled once the spacers have bween added.
15 Once the blower is bolted...
15 Once the blower is bolted into place, the tubes are reinstalled.
16 Everything is buttoned...
16 Everything is buttoned up and we decided to leave off the stock intake manifold cover.
17 Kevin MacDonald, lead...
17 Kevin MacDonald, lead calibrator at JPC Racing, checks over the tune to ensure all is good to go before making any runs.
18 Burcham succumbed to peer...
18 Burcham succumbed to peer pressure and grabbed a 2.75-inch Carbonite pulley. The smaller-diameter pulley bumped the boost to 20.5 psi and brought impeller speed slightly past its maximum efficiency rating of 60,000 rpm. At 7,200 rpm, the impeller was spinning a little more than 62,000 rpm (crank pulley/blower pulley x step-up ratio x engine rpm).
We wanted to show the difference...
We wanted to show the difference between the two pulley drive combinations. The eight-rib pulleys with a smaller supercharger pulley increased boost from 15 psi to 20.5 psi. The real story is that this engine makes peak power at 7,200 (stock cams and stock intake) and peak came at just 6,600 with the six-rib pulleys because the belt slipped after that point, bringing boost down to 13.5 psi and hurting power. The boost was at 15 psi for the peak power output with the six-rib configuration. The eight-rib pulleys did spin the supercharger harder, but the belt didn't slip and boost shot up to 20.5 at 7,200 rpm for a peak power rating of 1,032 rwhp.
Here is a graph comparing...
Here is a graph comparing the two best dyno runs with either pulley configuration. The blue represents the eight-rib combination and the red is the six-rib setup. The power difference is rather drastic and exaggerated due to a 2.75-inch pulley for the big power runs and just a 3.10-inch pulley for the 843-rwhp performance.