By Titus Bloom:
Superchargers are magical devices. They increase the oxygen supply to the engine by compressing the air, thus increasing its density. Accordingly, the engine burns more air-fuel mixture and produces more power.
In a centrifugal supercharger, the air is propelled through the compressor wheel and compressed in the diffuser—the thin passage formed between the compressor cover and the bearing housing—and in the volute or scroll where its kinetic energy is converted to pressure. All of the dimensions, including the diameter of the diffuser, diffuser gap distance, size and diameter of the volute, contribute to the degree of compression.
In a turbocharger—exhaust-driven forced induction—the compressor wheel is powered by exhaust flow, but in the supercharger the compressor wheel is driven via a gearbox that takes its power from a crankshaft pulley by way of a drive belt. The gearbox accelerates the compressor wheel from engine speed to a point where the compressor operates efficiently.
Here below is the assembly process:
Compressor wheels comprise eight main blades with a shorter splitter blade between each. The complex profile of the compressor wheel fits the inlet port of the compressor cover precisely. The axial and radial clearances between blades and the cover in which the wheel rotates are 0.021in to 0.023in.
To increase durability, this supercharger has a dedicated, self-contained oiling system and runs ceramic ball bearings. Four in number and made of silicon nitride, ceramic bearings are smoother, harder and lighter than their steel counterparts.
During manufacture, each compressor wheel, shaft and retaining nut is balanced as an assembly to 0.3g-mm and marked by a vertical blue line. Later in the build the alignment is repeated—if not, the balance will be lost.
By gripping the compressor wheel shaft gear underneath and tensioning the left-hand thread retaining nut on top the assembly is secured.
Upon close inspection, two small squares of translucent wax sheet positioned 180 degrees apart are visible. These are used to gauge the clearance between the compressor wheel and cover.
Clearance between wheel and cover is specified at 0.021 to 0.023in. This is significant because warming aluminum compressor wheels grow and, hence, critical they don’t touch the cover while operating at around 70,000rpm.
For strength this manufacturer uses tool steel straight-cut pulley gear assemblies, which are hobbed, precision-ground and balanced. Made in two parts the shafts are frozen in liquid nitrogen then inserted into the gear wheel.
For easier bearing fitting, the gear wheel is stored in frozen conditions, enabling the shaft to enter the bearing bore without being forced. The other bearing journals on view accommodate the pulley and key, seal and bearing respectively.
This unassuming billet of 7075 aluminum is the compressor-wheel blank, which plays a pivotal role. Each component is blueprinted, hence the number 89 identifies its entity and its subsequent many dimensional details are recorded.
With simultaneous 5-axis machining centers, TorqStorm not only produces their own complex supercharger compressor wheels but also production quantities for other turbocharger manufacturers.
The tolerance in distance between these two shaft centers is held to 0.0002in. Note inner perimeter O-ring which seals gearbox housing to cover.
Viton seal nesting in the lower section of the bearing housing and Smalley wave springs in the upper. Understandably, maintaining axial and radial position of the compressor wheel and pinion gear is crucial.
Emphasis is focused on engaging the cover on the two dowels cleanly—one positioned at each end—lubricating the seal and ensuring the cover is located with care. A 3.250in eight-rib pulley will eventually be installed on the protruding pulley shaft.
Dissimilar metals are separated by an anti-seize compound. Fourteen stainless steel socket head bolts, which measure 0.025in diameter x 20tpi x 1in long, clamp together the 6061 billet aluminum gearbox case and cover.
To prevent binding in the bearings, the gearbox cover bolts are tightened to the housing in correct sequence. Also, clamping pressure and thus correct bearing settings is achieved by final torque wrench setting: 8lb ft.
Remove drain plug. Gearbox receives 6fl oz of specially formulated synthetic oil developed by Royal Purple for the supercharger’s self-contained lubrication system. Oil is changed every 10,000ml during normal use and annually under severe duty.
When connecting the supercharger cover to the main body, the chief advantage of employing a V-band is convenience. Whether the outlet port is directing its pressurized charge to a carburetor, throttle body or intercooler, the V-band provides infinite radial adjustment.
It’s the details that impress: every supercharger is blueprinted, hand-built, dyno-tested prior to shipment and provided with a limited life-time warranty.
Early cast aluminum versions of this design deflected and necessary tolerances could not be maintained. TorqStorm switched to tempered 6061-T6 billet aluminum alloy, which contains magnesium and silicon. The diameter of this outlet port measures 3in; the inlet 3.5in
Rick Lewis (616) 706-5580