Although they run a tight 0.003 to 0.004-inch rotor-to-rotor and rotor-to-case clearance, the KB rotors never touch each other or the case. This is a tough trick; uneven heating along the length of the supercharger makes rotor alignment difficult, yet critical, to maintain. In fact, the higher cost of twin-screw superchargers is directly attributable to the difficult job of machining these complex rotors. It takes a $1 million cutting machine to do it, so the opportunities to explore the latest in rotor shapes is limited either to those with the machinery or to those who have connections to it. Kenne Bell falls into the latter category, as its rotors are all machined in Sweden.
Increased boost pressures mean higher temperatures and stresses on the supercharger. This leads to rotor flexing and a need for tougher rotor supports in superchargers designed for high output. This cutaway of the Kenne Bell rotor illustrates how the rotor is located by a stout bolt and twin rows of roller bearing. Because this assembly is at the cooler, less-stressed intake end of the supercharger, these parts are smaller than at the drive end, but the twin row bearing speaks volumes about the critical need to maintain rotor alignment.
Moving to the front of the supercharger, the mounting hardware, and especially the ball bearings, is much larger. This end of the supercharger also absorbs the drive loads from the helically cut pair of drive bearings.
Inside the blower-drive snout, there's nothing new in the latest Kenne Bell superchargers. That's because KB has been making its own drives for years without issues, so there was no need to change this section for the new supercharger. It's interesting to see how thrust loads are cushioned by a coil spring, and how the drive's axial forces are damped by surprisingly hard plastic pieces between the gear and driveshaft. This end of the case is stoutly built to absorb both drive gear and belt loads, in addition to the internal supercharger forces.
Closely inspecting the blower's drive pulley shows the small hole centered in the Allen-headed attachment bolt. That hole vents the blower drive; the two unthreaded holes flanking the Allen bolt are locators for the pulley replacement tool sold by KB. They are part of Kenne Bell's fast and easy pulley changing design. Almost all of KB's Ford blowers use six-rib drive pulleys to retain compatibility with the remainder of the front engine dress (alternator, water pump, and such). KB notes that a large-diameter six-rib pulley with its inherently generous belt wrap is effectively an eight-rib system when it comes to transmitting force.
Kenne Bell blowers are all self-contained oilers. A dipstick is provided to keep tabs on the blower's oil level and color; the oil goes black when overheated. Otherwise, it has a honey-color dye added to it to raise visibility on the dipstick. Maintenance is simple: change the oil every 10,000 miles with Redline 50W synthetic or 50W Mobil 1. There is no drain, so you'll have to swipe your wife's turkey baster to suck the oil out through the dipstick hole.
Kenne Bell's strategy to make a larger blower was to increase the rotor bore and keep the exterior size the same. Holding the new end plate (bare aluminum) over an older end plate (black) shows the increase in bore diameter. The plates are CNC-machined and doweled to the case for positive location.
The two cooling pods on the front cover of the new superchargers are the easiest way to spot the new Kenne Bell blowers. These pods give a little extra oil volume and cooling at this warmest part of the supercharger. The new blower in front has them (they look like blisters for gear clearance but aren't); the older unit in back does not have them.
The size and shape of the blower's entry and discharge apertures vary depending on the displacement, design rpm, and output of the supercharger. The important point is the inlet and exit are carefully sized to maintain an intake/discharge ratio. Jim Bell reports these new superchargers will take 15 hp less to drive and run 20 degrees cooler than his previous twin screws; the more efficient inlet and discharge ratios and improved rotor profiles are why.