3 Different Ways To Supercharge Your Mopar - There's No Bad Way To Be Blown
Roots-Style, Screw-Type, And Centrifugal Superchargers Offer Three Ways To Supercharge Your Mopar
From the January, 2010 issue of Mopar Muscle
By Dave Young
Photography by Courtesy of the Manufacturers, Dave Young, Kevin DiOssi, Randy Bolig
There are some decisions we make in life that have no bad outcome. Like visiting the ice cream store, no matter what flavor you choose, you're still having ice cream. Similarly, there are choices we make when building our Mopars, but whether Hemi, big-block, or small-block, A-, B-, C-, E-, or F-body, the end result is still a Mopar so there's really no bad choice. The same goes for supercharging the engine in your Mopar. Regardless of which style you choose, Roots, Screw-Type, or Centrifugal supercharger, you'll still be force-feeding air and fuel into your engine for incredible power gains.
When it comes to power, the secret of supercharging has been out for a long time. In fact, most supercharger designs predate the invention of automobiles altogether. As an example, the Roots supercharger design can be traced to the American brothers Francis and Philander Roots, who came up with the design in 1854 as they attempted to improve the design of the waterwheel powering their textile mill. Though their bi-rotor gear pump didn't work very well at the water mill, the brothers later found it to be great at pumping large volumes of air. Before being adapted to automotive applications, Roots and other styles of superchargers were used in a variety of industrial applications, including blowing fresh air down mine shafts.
This front engine dragster...
This front engine dragster with dual blown Hemis was for sale at the Mopar Nationals last year. We're not sure if it was a replica or the real deal, but it demonstrates the common use of blowers on Hemis, in this case two of each, during the early days of drag racing.
The first application of a blower being fitted to an internal combustion engine is arguably when Sir Dugald Clerk used one on his two-stroke engine design in 1901, forcing air into the engine in an attempt to lower the inlet air temperature. While compressing air actually raises the inlet temperature, he did discover that he increased power by some six percent using forced induction. Since then, superchargers of many types have been designed and used to force air into internal combustion engines with varying levels of success, and through that process modern superchargers have evolved into one of three basic designs. Today, nearly all automotive supercharger systems are Centrifugal, Roots, or Screw-type, and fortunately there are some extremely well-engineered and reliable systems available for our Mopars new or old. With modern intercoolers to lower inlet air temperatures, there's just about no limit to the power you can make with any of these supercharger systems.
Centrifugal Superchargers Named for their inertial compressor, Centrifugal superchargers offer manageable boost, in a small package for easy underhood mounting.
While the Centrifugal supercharger may look more like what we think of as a turbo rather than a blower, it is engine driven by pulleys or gears and thereby is considered a supercharger. Though not driven by exhaust gases like a turbocharger, the Centrifugal supercharger does share the same type of inertial compressor. This style compressor requires high rpm, sometimes 50,000, so the compressor rpm is multiplied by a precision gear-case with bearings which can be oiled either by engine oil, or by a self-contained oiling system.
Centrifugal superchargers systems are easy to install, and a reliable way to get more power from your Mopar. Most street, or even stock factory engines with cast internal parts can easily handle moderate amounts of boost without sacrificing reliability.
Unlike Roots and Screw type compressors, the centrifugal compressor, sometimes called the impeller, is not a positive displacement pump, so boost increases gradually as a function of rpm. This makes the centrifugal supercharger a great choice for street cars, especially those that are traction limited. By virtue of its design and smaller size, centrifugal superchargers can be mounted further from the intake, making them somewhat easier to intercool and keeping the compressor away from the engine, reducing air inlet temperatures.
"Big Daddy" Don Garlits had...
"Big Daddy" Don Garlits had an extremely successful career in Top Fuel, using Roots style blowers with nitro methane fuel almost exclusively. Big Daddy is still at it, making exhibition passes in one of his early "Swamp Rat" diggers as recently as the Mopar Nationals.
Most centrifugal superchargers use a belt from the crankshaft to drive the gear-case, but in extreme, high-boost applications a cogged belt or even gear-drive is sometimes necessary. Manufacturers make centrifugal superchargers in all sizes, and most come as complete kits with all the necessary components. For older muscle cars, systems are available that blow through the carburetor, and for modern Mopars the kits come with new fuel injectors and computer programmed tuning. Centrifugal supercharger systems offer great power, good reliability, and are relatively easy to install for the average mechanic.
Vortech, Paxton, and ProCharger...
Vortech, Paxton, and ProCharger all manufacture quality centrifugal supercharger systems. For the new Hemi, a centrifugal supercharger sits hidden under the hood in most cases.
This diagram shows the various...
This diagram shows the various types of superchargers, or blowers, designed over the years. Today nearly all popular automotive superchargers are Centrifugal, Roots, or Lysholm Screw designs.
For carbureted applications,...
For carbureted applications, the supercharger can be ducted into the carb, commonly called a blow-through system.
The classic hotrod supercharger is the Roots, or Eaton style blower. Aside from its intimidating looks, the Roots blower offers increased power at the crack of the throttle.
Roots, or Eaton-style, superchargers are probably the most recognized blowers in the world. As a Mopar lover, you might not like the fact that modern Roots blowers evolved from the GMC 6-71 blower developed in the 1930s, but you have to love the fact that blown Hemis using this type of supercharger have continuously dominated the top classes in drag racing for many years. There are no GM parts in modern Roots blowers, however, because manufacturers such as Littlefield, Eaton, MagnaCharger, BDS, and Holley/Weiand build completely new Roots blowers and blower kits for almost any application.
Roots superchargers have powered...
Roots superchargers have powered some of the quickest and fastest drag racing cars in history, providing instant power at the crack of the throttle. Modern Roots systems are compatible with new and old Mopars, even fitting under the hood in certain applications.
The classic drag racing combination...
The classic drag racing combination is a bug-catcher air intake atop an injected, blown race Hemi. By design, the Roots blower is difficult to intercool, but there are some manufacturers making air/water intercoolers that are sandwiched between the blower and intake.
Roots blowers might be considered...
Roots blowers might be considered old-school to some, but they're still widely produced, available in kit form, and can be a great way to get impressive power numbers from the engine in your classic or modern Mopar.
To properly meter fuel, Roots...
To properly meter fuel, Roots blowers that are mechanically injected engines use a barrel valve. This is what you see the crew chief adjusting prior to each Top Fuel quarter-mile pass. Most street cars use either electronic fuel injection or carburetors with their blowers.
Most Roots superchargers on...
Most Roots superchargers on classic Mopars are topped with one or more carburetors. These systems are actually fairly simple to install, and can be very reliable if set up and tuned properly. So if over the top looks and power are your style, a Roots supercharger may be just what you need.
With the rear air-inlet plate...
With the rear air-inlet plate removed, you can see the male and female intermeshing rotors inside the screw-type supercharger.
Centrifugal blowers can also...
Centrifugal blowers can also be ducted into an airtight box abound the carburetor. Under boost conditions, the entire box is pressurized, forcing air through the carb.
The compressor of the Roots blower is a positive displacement pump, containing two rotors spinning inside the blower housing to pump air. Early Roots blowers had either two or three-lobe rotors that were straight cut, but modern designs utilize helical rotors with Teflon seals to form a tight clearance between the rotors and the housing. Either way, the air or air and fuel enter the top of the blower, and the mixture is then pumped outward and down the inside of the rotor case, exiting at the bottom. This style of blower typically sits right on top of the engine which creates higher inlet temperatures than centrifugal superchargers. Roots-style blowers are also more difficult to intercool, though there are air/water intercoolers that sit between the blower and the intake.
Thanks to modern computer...
Thanks to modern computer and manufacturing technology, high-quality materials, and high-tech engineering, centrifugal superchargers are reliable and easy to install, offering great power for their cost.
The latest Roots blowers with "high-helix" rotors are even more efficient than the original design, and reliable Roots supercharger systems are now available for modern and older Mopars, both carbureted and fuel injected. By design, the roots blower provides instant boost for incredible torque and throttle response, even from an idle. Race units are generally set up for mechanical fuel injection to handle the large volumes of fuel required, and injectors can be mounted on top of the blower in the injector "hat" (helping keep the mixture cooler), in the intake below the blower, or in extreme cases, injectors can be installed in both locations. Roots superchargers are also compatible with electronic fuel injection, and small roots blowers can provide big power increases on otherwise stock late model Mopars. Another common setup for older cars is dual carburetors on top of the blower, though this method generally requires cutting a hole in the hood, allowing the world to see your massive display of power.
Screw-type superchargers look...
Screw-type superchargers look similar to Roots units, but actually perform much differently. The Mr. Norm's race team uses a Kenne Bell supercharger on their modern Hemi to run some impressive mid-nine second elapsed times in the quarter.
Screw-Type superchargers, also known as twin-screw, or Lysholm compressors, are very similar externally to Roots style superchargers. They are both positive displacement pumps, and each house a pair of multi-lobe, helical, meshing rotors. But while the two rotors of the screw-type are contained in a case that usually sits atop the intake, just like the Roots, internally, the units are engineered very differently. First, the rotors in a screw-type compressor spin toward the center, or down where they meet, instead of toward the case, or up where they meet, like a Roots supercharger. Next, the rotors of a screw-type blower having a male and female rotor instead of symmetric rotors like the Roots.
Based on an evolved version of a simple screw-type water pump developed by the Greek inventor Archimedes around 200 B.C., the intermeshing spiral rotors of a modern screw-type supercharger are precisely engineered for maximum efficiency. By design, the screw-type blower both moves air forward along the rotors as a positive displacement pump, and also acts as a vane supercharger, further compressing the air as it moves it. This combination of air compression gives screw-type superchargers higher efficiency ratings, and lower inlet air temps, especially at high boost levels, when compared to Roots blowers.
Years ago, the complicated machining required to fabricate the rotors of a twin-screw compressor restricted the design to industrial applications, but thanks to CNC machining the cost to manufacture these parts have dropped significantly. Kenne Bell, Whipple, and Vortech-Lysholm are all producing screw-type superchargers and supercharger kits for modern and classic cars, including Mopars. Twin-screw systems generally give more hood clearance than Roots superchargers, as air can enter at the rear instead of the top. The screw-type supercharger also needs less maintenance than the Roots, since no Teflon seals are required on the rotors, making it a great choice for your Mopar.
Whatever style blower you...
Whatever style blower you choose, it will be driven by the crankshaft by either a belt or gear drive. Street systems normally utilize a serpentine belt, often shared with the rest of the accessories, while high-boost units need a cogged belt to prevent slippage.
The technology behind supercharging...
The technology behind supercharging can't all be covered in one magazine article, so if you want to learn more check out The Complete Guide to Street Supercharging by CarTech.
Screw-type superchargers have...
Screw-type superchargers have very high efficiency ratings, but are somewhat more complex to manufacture than Roots or centrifugal blowers.
Kenne-Bell already has screw-type...
Kenne-Bell already has screw-type supercharger kits available for the 5.7 and 6.1 modern Hemi engines, enhancing an already potent platform.