Positive-Displacement Supercharger

[DRAG Boosted Si]

There are two basic styles of superchargers: positive displacement and centrifugal. Each type has its own advantages and limitations. Also referred to as Roots-type units, positive-displacement superchargers are classified as such since every revolution of the blower pumps out a fixed volume of air, regardless of the blower's RPM.
The result of this is that boost comes on in an instant. With this family of superchargers, the amount of boost is dependant on the blowers size, the engine size, percent of over-/underdrive, rotor clearances and the volumetric efficiency of the engine. As blower size is increased, boost pressure also increases. This results because the blower is pumping a greater volume of air than the engine can ingest, so the air not making its way into the engine is put under more pressure.
The Size of the engine also affects boost level. As an engine's size increases, boost pressure drops because a greater percentage of the air displaced by the blower can make its way into the larger engine. On Positive- Displacement Blowers, boost can also be adjusted by varying the pulley sizes on the engine and blower
In addition to the already mentioned factors, the breathing ability (volumetric effiency)of the engine also affects the boost level. Engines with ported cylinder heads, healthy camshafts, and aftermarket intakes with register a lower boost level than a stock engine. This is because the modified engine breathes as if it were a larger stock engine--from what we already know, a larger engine lowers the boost level. In general, positive-displacement superchargers are unmatched in the area of boost response
As for the limitations, positive-displacement superchargers do not match the adiabatic effiency of a centrifugal supercharger or turbocharger. As a result, charge air temperatures for a particular boost level on an engine are typically higher than the same engine with a centrifugal supercharger. additionally, positive displacement superchargers are usually incompatible fits that these systems can provide.
For Honda's most popular engine platforms, Jackson Racing offers a supercharger system. This bolt-on system uses an Eaton positive-displacement supercharger. This Roots-type blower is the preferred choice of many OEM vehicle manufacturers due to its durable design. Its durability is the result of close-tolerance, CNC-Machined Rotors. These rotors are epoxy-coated for extended service life. The oiling system for the supercharger is self-contained, making installation straightforward. A unique by-pass valve reduces the load on the supercharger under part-throttle. Making the authorities happy, the systems feature 50-state legal certification