The 3.6:1 step-up ratio offered by the internal gears is identical between the two superchargers. This ratio is important when trying to determine impeller speed. Here is the formula used to figure out the impeller speed at a given rpm: crank pulley blower pulley x 3.6 (step-up ratio) x rpm. Putting that formula into action looks like this: 8 inches 3.33 inches x 3.6 x 5,900 rpm = a maximum impeller speed of 51,027 rpm at the 5,900-rpm limit plugged into the formula. This formula will work with any centrifugal super-charger. Be sure to adjust the step-up ratio as different superchargers feature different ratios.
As we mentioned earlier, Paxton will continue to offer oil-fed and self-lubricating blowers, giving the customer another option when selecting a supercharger. The engineering of the SL was not as consuming as one might have thought.
"We began the project last year and had preproduction models by this past spring,"Best says. The major hurdle in the conversion was controlling the oil inside the blower. Engine-oil-fed units essentially spray a mist of engine oil into the case to keep the gears and moving parts lubricated. A small orifice controls the volume of oil required for adequate oiling, which isn't much when it's spraying. A self-lubricating unit requires a greater amount of oil-4 ounces, according to Paxton's technical manual. The extra oil presented some problems with circulation and foaming. Paxton engineers modified the internals through trial and error, ensuring longevity and high performance. They used plastic windows to observe the internal workings while the test units were running on the in-house blower and engine dynos. A final version was produced and subsequent testing commenced.
Real-world testing included hours upon hours on the engine and chassis dynos to ensure horsepower and torque were in line with the oil-fed units. Paxton representatives report the horsepower ratings are identical in both applica-tions. After the barrage of dyno testing was completed, the blower was sent out to the real world. Thousands of miles were logged in various engineering vehicles. The entire conversion process took nearly a year to complete, and Paxton debuted the SL blowers this past summer.
MM&FF was one of the first to get a production SL blower, and we turned to John Franco to test the unit. His '06 Mustang GT has been the subject of a few MM&FF tech stories in the past. Currently, Franco's Pony has a Paxton high-output supercharger system on top of the stock Three-Valve engine. We installed the kit in the March '07 issue ("Feeling The Pressure"), and it performed nicely with 475 rwhp using a conservative computer tune-up, according to Turbo People's Job Spetter. This time around, we bolted on the SL unit to replace his oil-fed piece and also upgraded the pulley system to an eight-rib configuration.
The hardest part of the installation was pulling off the stock pulleys and replacing them with the Paxton eight-rib upgrade kit. Included in the kit is an assortment of pulleys sourced from '03-'04 Cobras and Paxton's parts bin. The Cobra parts are brand-new pieces that Paxton gets from Ford. Spacers for the blower brackets are also in the box. "It's important to convert to the eight-rib pulleys if you plan on turning up the boost. They offer greater belt traction to prevent slippage," says Best.
On the dyno, the blower worked nicely as horsepower and torque readings registered 476 and 417, respectively. The cool thing about this car is that it still wears stock headers and features a Bassani x pipe system with cats, mufflers, as well as a set of rear gears. As long as Franco keeps his right foot under control, the car exhibits similar fuel mileage as it did when it was bone-stock.
A drain hose is attached to the bottom of SL blowers. It allows the user to drain the supercharger without having to unbolt it from the brackets. | 
Paxton requires 4 ounces of special oil to fill the supercharger. It's a special lubricant that has been spec'd out by Paxton. Oil changes are required every 12,000 miles or once a year. | 
We had to remove a slew of parts to perform the eight-rib pulley swap. The blower was removed and eventually replaced with the NOVI 2200 SL. Other parts that were set aside for the swap were blower piping, inlet pipes, the fan shroud, and eventually the electric fan. |
Here's what was left in the engine compartment once those pieces and parts were removed. | 
Perhaps the hardest part of the eight-rib pulley swap was removing the alternator pulley. It requires a special tool that is offered only through Ford dealers and Saleen. As you can see, there are splines on the inside of the pulley. It was 10 o'clock at night when we started working on Franco's car, and we were unable to get the tool. We rigged up something to get the job done-it was definitely not the right thing to do, but we were tired. Let's just say that we were lucky the pulley didn't have to be reused. | 
Adding the larger pulleys meant we'd have to space out the supercharger mounting brackets. Here, the stock tensioner was fastened to spacers and bracket. |