The roots blower's bulky shape...
The roots blower's bulky shape and long discharge slot makes intercooling difficult. Here, a small water-to-air intercooler is placed in the plenum below a roots blower.
There are two types of superchargers commonly found in the aftermarket: positive displacement superchargers like the Eaton roots supercharger and centrifugal superchargers like the Vortech, Procharger, Rotrex, Paxton, HKS and Powerdyne systems. Both have totally different power characteristics. It's important to understand those characteristics for you to choose which type best suits your needs. On a side note, there's also the enigmatic Lysholm supercharger, a system with a lot of potential but with few applications.
Positive Displacement Superchargers
Positive displacement superchargers begin by taking a fixed volume of air in a chamber and moving it into a second chamber at a rate higher than the second area can be emptied. This backup of air results in pressurization of the air inside the second chamber thus increasing its density. The amount the air moves depends on the volume of the first chamber and how quickly and how many times the chamber's filled and its contents transferred. The difference between the volume of air pumped by the supercharger and the volume of air consumed by the engine is how positive displacement superchargers achieve positive manifold pressure. Such superchargers are often called "blowers" in hot-rodder lingo.
The advantage of positive displacement type blowers are their immediate and proportional boost response in relation to the throttle; such blowers consistently pump a given, constant volume of air despite engine speeds. Of course, there are slight variations in boost pressure as a blower's and an engine's volumetric efficiency improves and declines alongside engine speed throughout the powerband but, for the most part, boost pressure remains fairly constant. This makes a positive displacement blown motor feel like you're packing a much bigger engine than you are.
Some centrifugal blower's...
Some centrifugal blower's step-up drives are belt driven to avoid whining sounds typically associated with gear drives.
Because of these characteristics, a positive displacement supercharger is the king of driveability and low-rpm power-the perfect characteristics for a daily driver or for those who value low-end grunt. Such grunt is welcomed in high-revving, small-displacement engines like Honda's B16A and B18C. The constant delivery of boost pressure makes for an engine with smooth, linear power delivery characteristics making the positive displacement blower ideal for the driver who values a 1:1 relationship between the gas pedal and the amount of power produced. Autocrossers who need smooth predictable power from very low speeds to help throttle steer through tight cones or a person who just wants a tractable, predictable street-driven car with plenty of right-now, no-waiting punch to quickly end stoplight encounters will appreciate it too.
Roots blowers are the most common positive displacement superchargers. They're found in industrial applications like school buses, stationary engines such as generators, industrial compressors and air pumps. A roots blower has rotating, intermeshing lobes that displace a greater amount of air than the engine does. This is due to both the blower's pumping volume and stepped-up rotor-drive ratio, which is usually around two to three times the crankshaft speed. The roots blower does have some disadvantages besides the obvious parasitic loses though. Its large internal volume means that the blower has to be big and bulky, making it difficult to package near a crank drive in a tight engine compartment. Its size, shape and long discharge plenum also means it's difficult to intercool.