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Message: <blockquote data-quote="blown98gt" data-source="post: 596046" data-attributes="member: 11284">Through a lot of reading and writing and combining information i've put this together hope it'll help solve some of the questions that seem to pop up a lot. If you need to use the ctrl + F to find certain information. Links to most of the common s/c sites are the the bottom. The 2 main types of superchargers are covered below and both pro's and con's to both. There is a ton of information here and I understand there is a lot so just read and enjoy.Superchargers, how to choose one, what makes one better than the other, In general terms, a supercharger, which is also commonly known as a blower, is nothing more than a large air pump that is driven by a belt that runs off the crankshaft of an engine. Superchargers have been used on car engines for more than a century already and are nothing new.A more pertinent consideration should be what supercharger to use, especially with all the different types of superchargers available these days. Choosing the best supercharger for your particular engine can be a bit of a challenge as no single supercharger can be described as "the best". All superchargers work well, and they all have their strengths and weaknesses. What you need is an idea of what you want from the supercharger and an idea of what to expect from each type of supercharger. Especially as different vehicles and different engines may benefit from one type or another; so it's important that you know what you're looking for.There are two types of superchargers that are commonly used on an internal combustion car engine:  1* Centrifugal superchargers, which are very similar to turbochargers;  2* Positive-displacement superchargers, such as the Roots supercharger and the twin-screw supercharger.The Roots Supercharger<img src="http://www.capa.com.au/pics/eaton_diagram2.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" />The Roots supercharger, or the Eaton supercharger as its also called, is the oldest type of supercharger around, having been designed by the Roots brothers in 1859 as an air pump for use in the mining industry. The Roots or Eaton supercharger is a positive-displacement supercharger that consists of at least two lobed rotors housed in an aluminum casing. The rotors are meshed together and geared to rotate in the opposite directions. As the lobes turn, air trapped in the space around the lobes and is forced along the inside of the casing until it is discharged into the intake manifold. Being a positive-displacement supercharger, it moves air at a fixed rate in relation to engine RPM; hence a larger capacity Roots supercharger is required if you want to achieve higher boost levels.However, the Eaton supercharger and the Roots supercharger does not compress air but simply moves air at a fixed rate in relation to engine RPM. In this sense it is nothing more than an air blower with air compression taking place externally. In other words, the Roots supercharger produces boost pressure by stacking more and more air into the intake runners and into the intake manifold. Thus, with the Roots and Eaton supercharger, boost pressure is the result of more air being forced in to the intake runners and into the intake manifold and boost pressure only increases after the air is discharged from the supercharger. Hence the Roots supercharger is also called an external compression supercharger. This external compression is also a major contributor to the relatively poor thermal efficiency of the Roots supercharger.THE PROS & CONS OF ROOTS-TYPE SUPERCHARGERSIf you're looking for a cost effective, low boost supercharger with excellent boost at low RPM then the Roots-type supercharger may just be your best option. However, these types of superchargers do suffer from internal leakage, which reduces it efficiency at low RPM. Furthermore, the Roots supercharger draws the most engine power of all types of superchargers and also has the least thermal efficiency of all superchargers. However, its simple construction with few moving parts makes the Roots supercharger one of the most reliable types of superchargers you can find. The Roots supercharger also doesn't suffer from surge as it is a positive displacement supercharger, which means that it moves air at a fixed rate in relation to engine RPM. This also means that a large capacity Roots supercharger is required if you want to achieve higher boost pressures. However, if you're looking for boost pressure of over 12 psi, you'd have to look elsewhere as the poor thermal efficiency of the Roots supercharger becomes a major problem at higher boost pressures. Although, they work wonders on exotic fuel dragsters that are used for short bursts of around 15 to 20 seconds at a time and were boost from low RPM is more important than thermal efficiency, they are not ideal for constant high boost applications.THROTTLE PLACEMENTWhen implementing a Roots supercharger, you must install a bypass valve and relocate the throttle body ahead of the supercharger's inlet port. If you don't move the throttle body, the supercharger will build up pressure between the supercharger and the throttle whenever your foot is off the accelerator, such as when you're idling, decelerating, or changing gears. When the pressure between the supercharger and the closed throttle exceeds the boost pressure being supplied by the supercharger, the air will be forced back through the supercharger. However, air can only move in one direction through a Roots-type supercharger. If the air tries to flow back through the supercharger, the supercharger will cease and will destroy the drive belt. This can also cause the throttle plate to buckle and get jammed in the throttle bore as the pressure will not be released. Of course, moving the throttle body further away from the intake valves will make the engine less responsive to throttle input, but that's just the cost of running a positive-displacement supercharger.</blockquote>