Automotive superchargers fall into two categories: positive displacement and centrifugal. Centrifugal superchargers are basically like the compressor side of a turbocharger, driven by a belt from the crankshaft through some sort of overdrive device, either a second belt drive or gears. Air flows continually and is compressed inside the housing, giving centrifugal superchargers high efficiency, especially important at high boost pressures. Centrifugal compressors, because of their high-speed operation, can move a lot of air relative to their physical size, typically making them easier to package in an engine compartment. For this reason, and because lag is not an issue as it is with turbochargers, the compressor can be comparatively large, further enhancing efficiency at high flow rates. A small number of moving parts reduces manufacturing costs and enhances durability. Unfortunately, while lag is not an issue, dynamic characteristics remain a problem, to the extent that some pundits say a centrifugal supercharger combines the weaknesses of a turbocharger and a supercharger. The potential pressure ratio developed by a centrifugal supercharger is roughly proportional to the square of the compressor's rotational speed. This means that boost rises nonlinearly with rpm and power is biased strongly toward the top end. This can be seen clearly in the dyno tests we have done on supercharged cars. The most extreme case was a 1.6L engine which gained roughly 50 bhp over each of the last 1000 rpm, the result being 272 hp at the wheels at 7900 rpm, the last data point, before fuel cut.
An impressive number, to be sure, but completely unusable. The "Bosch Automotive Handbook," 4th Edition, states on page 380 that centrifugal compressors "are not suitable" for vehicle engines. This is qualified on page 424, where it is stated that "a transmission unit must be included to vary the rotational speeds if the pressure is to be maintained at a reasonably constant level over a wide range of flow volumes (i.e., engine speed)." The accompanying diagram suggests a continuously variable belt-drive transmission.
Centrifugal superchargers have proven especially popular with owners of musclecars, whose vehicles typically have healthy low-speed torque but need a boost at high rpm. Nevertheless, a wide variety of European applications have found their way to market, most based on the superchargers of just three manufacturers: Z Engineering, Powerdyne and Vortech, the latter claiming the lion's share of volume at present. Paxton and Turmat are two more manufacturers of centrifugal superchargers, but we are not aware of any currently viable European applications of these units.
Positive displacement superchargers fill a chamber of a fixed volume with air at atmospheric pressure and move that air to the high-pressure side. The mass flow rate of the air thus moved depends primarily on the volume of the initial chamber and the speed of operation--i.e., how many times that chamber is filled and its contents squeezed out the other side--and is relatively independent of pressure ratio. Positive displacement compressors generally give a flat torque curve throughout the engine's operating range and good throttle response.
The main drawback of positive displacement compressors is that the fill/discharge cycle is discrete or, more simply, lumpy: Air comes in bursts, rather than smoothly and continuously as with a centrifugal compressor. Adding to the problem is the fact that most positive displacement schemes compress the air simply by shoving it into the intake manifold. As a chamber of not-yet-pressurized air is opened to a manifold full of the already pressurized air, air first rushes from the manifold into the chamber, before being shoved back out into the manifold. Thus, much of the air is pumped twice, and it goes past the edges of the supercharger exit three times. The resulting turbulence heats the air, reducing compressor efficiency. As one might suspect, streamlining of compressor inlets and outlets becomes very important.
Perhaps the oldest positive displacement compressor is the Roots type, invented in the 19th century to ventilate coal mine shafts. These were room-sized, with wooden rotors. Later, between the wars, GMC used Roots blowers on two-stroke diesel truck engines, which were not self-aspirating. It was only a few years before the first hot-rodder put one on top of a V8 engine to go faster on the dry lakes. The big superchargers sold by B&M and Weiand, and used on Top Fuel drag cars, have their "roots" in these GMC units. Unfortunately, in addition to being sized for 500 c.i. engines, they are inefficient. Adding twist to the rotors can create some internal compression, as well as smoothing the flow, making it more continuous, and efficiency rises. The Eaton supercharger used as the basis of Neuspeed's new kit is a good example of this.
The Lysholm supercharger takes the concept of twisted rotors to its limit, so that it is often called a "screw-type" compressor. It complicates things even further with differential rotor speeds and is complicated enough that I can't get a clear picture of how it works in my head. (I expect to change this soon, when I hold the parts in my hands and play with them. Of course, you'll read about it.) The Lysholm compressor's advantage is that it achieves internal compression and thus high efficiency. There are currently three companies building Lysholm-type compressors, all in Sweden. One is not imported to the U.S., another is sold here as the Whipplecharger, with no European applications, and the third, Autorotor, is integrated for automotive use by several tuners.
The G-lader is a very old French invention, but required the precision and efficiency of CNC manufacturing techniques to be commercially viable. Volkswagen is the only company I am aware of to have used it extensively.
Sliding-vane compressors use an eccentrically mounted cylinder to drive centrally mounted vanes inside a housing of decreasing radius, providing internal compression. The Judson supercharger, popular in the '50s and '60s, was of the sliding-vane type. It was applied to many diverse vehicles, from Corvairs to MGBs. Obsolete, it has nevertheless achieved a small, all but invisible cult following among vintage car enthusiasts, and a surprising level of service is available.
The Wankel rotary engine was originally conceived as a supercharger, a purpose for which it is better suited than may appear on first glance. The rotor moves at only one-third crankshaft speed, meaning it can operate at high speeds, while it fills a chamber once each crankshaft revolution, meaning it breathes like a four-stroke engine of twice the displacement. The Wankel was used successfully, if not widely, as a supercharger before the focus changed to using it as an engine, and any surviving examples are most likely to be found either in a museum or slowly fading away in some German barn.
Advanced Motorsport Solutions
850 W. 18th St., Unit A
Costa Mesa, CA 92627
(949) 515-1672
Fax:: (949) 515-1676
www.advancedmotorsport.com
Vortech; Volkswagen
Bahn Brenner Motorsport
3402 C St. N.E., Unit 109
Auburn, WA 98002
(253) 833-2299
Fax: (561) 658-0423
www.bahnbrenner.com
G60 and Autorotor; Volkswagen
Bell Experimental Group Inc.
203 Kestrel Dr.
Spring Branch, TX 78070
(830) 438-2890
Fax: (830) 438-8361
www.bellengineering.net
Autorotor; BMW
Breyton Design
Giessereistraße 14
D-78333 Stockach
Germany
49-(0)77/715-270
Vortech; BMW
Climax Racing Products/CMF
10038 Canoga Ave.
Chatsworth, CA 91311
(818) 882-6691
Fax: (818) 882-8452
www.climaxracing.com
Vortech; Range Rover, Lamborghini
Dinan Engineering
150 S. Whisman
Mountain View, CA 94041
(650) 962-9401
www.dinanbmw.com
Vortech; BMW
Downing Atlanta, Inc.
5096 Peachtree Rd.
Atlanta, GA 30341
(770) 457-6300
Fax: (770) 458-6118
www.downingatlanta.comEaton; BMW
D&V Autotechnik GmbH
Einsteiner Straße 6
D-85716 Unterschleißheim
Germany
49-(0)89/310-3031
Fax: 49-(0)89/310-5920
Mercedes-Benz
Eurotech Inc.
(702) 368-7978
www.eurotechinc.com
Vortech; Mercedes-Benz
European Racing Technologies
12 Hadco Rd.
Wilmington, DE 19804
(800) 633-6007
(302) 633-1157
Fax: (302) 633-1063
Vortech; BMW E30 M3
Lorinser/Claus Ettensberger Corp.
16200 S. Figueroa St.
Gardena, CA 90248
(800) 766-0064
(310) 767-1111
Fax: (310) 329-3159
www.cecwheels.com
Vortech (modified); Mercedes-Benz
Mosselman Turbo Systems BV
Achterdijk 2
NL-4241 TG Arkel, The Netherlands
31-(0)183/561-839
Fax: 31-(0)183/561-840
Vortech; Mercedes-Benz
Neuspeed
3300 Corte Malpaso
Camarillo, CA 93012
(800) 423-3623
(805) 388-7171
www.neuspeed.com
Eaton; Volkswagen
New Dimensions Ltd.
2240 De La Cruz Blvd.
Santa Clara, CA 95050
(800) 637-2781
(408) 980-1691
Fax: (408) 980-1697
www.newdimensions.com/tec/
G60; Volkswagen
Race Marque Systems
14418 Oxnard St.
Van Nuys, CA 91404
(818) 778-6106
Fax: (818) 778-6109
www.racemarque.com
Vortech; BMW
Reigning Performance
(512) 454-4600
Vortech; Porsche
TURBO Performance Center
8040 Washington Blvd.
Jessup, MD 20794
(410) 799-7223
Fax: (410) 799-8523
www.turboperformance.com
Eaton; Porsche 996
Supercharger Manufacturers
(Centrifugal)
POWERDYNE(TM) Automotive Products
104-C East Ave., K-4
Lancaster, CA 93535 USA
(661) 723-2800
Fax: (661) 723-2802
www.powerdyne.com
Vortech Engineering Inc.
1650 Pacific Ave.
Channel Islands, CA 93033-9901
(805) 247-0226
Fax: (805) 247-0669
www.vortechsuperchargers.com
Z-Engineering USA
Pacific Trade Center
1660 Monrovia Ave. Suite E
Costa Mesa, CA 92627
(949) 515-7727
Fax: (949) 515-7737
www.z-engineering.com
(Positive Displacement)
Magnuson Products
3172 Bunsen Ave., Unit K
Ventura, CA 93003
(805) 642-8833
Fax: (805) 642-1936
www.magnusonproducts.com
For Eaton products