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Supercharger Design Choices

    Rather than make a list of all possible choices, these are some of the most common supercharger types, manufacturers, and models suitable for use on motorcycle and other small-displacement engines. Many are no longer produced but can be found on eBay etc. Click the link button for specific comments, then click the thumbnail for a larger view. Click for information on types not listed: .

Positive Displacement Type, Twin Rotor

Link

Mfg.

Rotation

Size, L

Ratio

Max RPM

Oil

Comment

Camden

1:1-1.25:1?

Chinn

1:1-1.25:1?

Eaton (Magnuson, Endyn, JRC &c.)

CW

.40-1.80

2:1-4:1

10-15,000

Oil bath

Italmechanica (S.Co.T., &c.)

1:1-1.25:1?

M.A.G. (Motosacoche, MAG)

1:1-1.25:1?

Magnuson (Magnacharger)

1:1-1.25:1?

Oil bath

Marshall

1:1-1.25:1?

Moss

1:1-1.25:1?

Nordec (Marshall-Nordec, Godfrey-Nordec)

1:1-1.25:1?

Pepco (PEPCO, Fageol)

1:1-1.25:1?

Roots (GMC, Dyer, Weiand, Holley Pro-Charger, &c.)

.75:1-1.5:1

Oil bath

Wade

1:1-1.25:1?

Volumex

1:1-1.25:1?

Positive Displacement Type, Twin Screw

Link

Mfg.

Rotation

Size, L

Ratio

Max RPM

Oil

Comment

Opcon Autorotor (SRM AB)

CW

.32-*

2:1-4:1

Oil bath

Positive Displacement Type, Eccentric Vane

Link

Mfg.

Rotation

Size, L

Ratio

Max RPM

Oil

Comment

Arnott

CW

.525-.825

1:1

External oiler

Centric

4,500

Cozette

G-Lader

Judson (Wray is similar)

External oiler

Shorrock

Zoller

Centrifugal Type

Link

Mfg.

Rotation

Size, L

Ratio

Max RPM

Oil

Comment

Drouin

2:1-4:1

Rotrex

CW

2:1-3:1

200,000

Internal pump, external tank

Positive Displacement Types

    This group, including twin rotor, twin screw, and eccentric vane types, mechanically captures a small volume of intake charge between two components and forces it into another state. Absent leakage, the transfer and compression are very efficient except for an increase in temperature proportionate to the boost. Some types are true superchargers where there is internal charge compression, and some are better described as blowers where the compression only takes place in the manifold. Higher boost rates increase the discharge temperature, which produces less effective power for the amount of boost.
    In general, positive displacement superchargers produce boost in direct proportion to their displacement per revolution (how much intake charge is captured by each rotation), and their rotational speed (except for leakage). E.g., a positive displacement supercharger turning at 10,000 RPM will produce twice as much boost pressure as the same unit turning at 5,000 RPM. This is most effective at producing power beginning at low engine speeds.
    The drive ratio between the engine and this supercharger type varies between slightly under-driven (1:.75) and highly over-driven (1:4), depending on the exact model and application, and always limited by the manufacturer’s maximum RPM limit.

Positive Displacement, Twin Rotor

    Generically known as “roots type”, these superchargers have two parallel intermeshed rotors turning in opposite directions. The rotors are radially and laterally symmetrical, and identical (except for the drive ends). The rotor-to-
rotor clearance is just sufficient to prevent contact. The rotor’s two or more lobes which may be straight or partially rotated (helix), and are generally driven by counter-rotating gears inside the front housing.
    The charge is not compressed except by the resistance (if any) in the intake manifold, therefore in the strictest sense these are not true superchargers but

blowers. The drive ratio between the engine and this supercharger type varies between slightly under-driven (1:.75) and somewhat over-driven (1:1.5), depending on the exact model and application (except as noted), and always limited by the manufacturer’s maximum RPM limit.
    The intake charge enters the housing on one side of the rotors (the top, as shown here), splits into two streams each of which is captured between a rotor lobe and the housing’s inner surface, passes around the outside of the rotors and is forced into the discharge side of the housing 180° away (the bottom, as shown here). The charge does not flow between the lobes. No charge passes between the rotors.

Camden

    This was a high quality unit made by . AFor more Camden information: .

Chinn

    Derek Chinn currently manufactures superchargers with capacity between 900cc to 3500cc per revolution. For more Chinn information: .

Eaton

    Eaton is the most common current original equipment supercharger, used by Ford, Mercedes, Jaguar, General Motors, VW, &c. They do not sell to the public, but the units are available from Magnuson and various other sources. The rotors twisted 60° along their length, which is an improvement over the straight rotored roots type.

    The charge flows from the intake port at the end of the rotors (axially), splits into two streams each of which is captured between a rotor lobe and the housing’s inner surface, and forced into the discharge port, as shown. This may be the top, bottom, or side depending on the orientation of the housing but the discharge is at 90° to the intake port. No charge passes between the rotors.
    The overdrive ratio between the engine and this supercharger varies between 1:2 and 1:4, depending on the exact model and application, and again always limited by the manufacturer’s maximum RPM limit. For more Eaton information: .

Eaton Superchargers

Model Number

M24

M45

M62

M90

M112

Displacement per revolution, Liters

.393

.737

1.016

1.475

1.835

Displacement per revolution, Cubic Inches

24

45

62

90

112

Sustained RPM

15,000

16,000

12,000

11,000

10,000

Maximum RPM

15,000

16,000

12,000

11,000

10,000

Italmechanica

    Also known as SCOT, S.C.O.T., S.Co.T., Supercharger Company of Turin, and I. T. Supercharger.
    This is similar to the Wade product and produced under a Wade license. For more Italmechanica information: .

M.A.G.

    This was a high quality unit by Motosacoche S.A. in Switzerland. Also known as “MAG”. For more M.A.G. information: .

Magnuson

    Also known as “Magnacharger. For more Magnuson information: .

Marshall

    The Marshall “cabin blower” was originally installed on light aircraft to compensate cabin air for high altitude. The most commonly used model (C75B) has a displacement of about 36” (600cc) per revolution. For more Marshall information: .

Moss

    This is a modern replica of the Marshall for smaller sports car engines. Moss also currently supplies what appears to be an Eaton for larger engines. For more Moss information: .

Nordec (a.k.a. Marshall-Nordec, Godfrey-Nordec)

    This was an automotive installation using the Marshall cabin blower as the core component, and was made by North Downs Engineering Company Ltd. For more Nordec information: .

Pepco

    Progressive Engine Products Company, Inc. made superchargers for VW from around 1950. Fageol sold them. Crofton took over from them about 1959. There were two case sizes, 4” and 6” lengths with remaining dimensions in common. For more Pepco information: .

Roots

    This manufacturer provided blowers for industrial air supply and purging diesel engines, some of which have been adapted and modified for automotive use. The name has become generic, including the common automotive and industrial BDS, B&M Automotive, Dyer, GMC, Hampton, Holley, Littlefield, Weiand, &c. almost all of which are too large and heavy for consideration for any but the

largest displacement engines. Even the smallest of these (3-53) is very bulky and inefficient compared to more modern designs such as the Eaton. For more Roots information: .

Wade

    This was available in twoi sizes. The RO20 is 2000cc displacement per revolution for engines from 2000 to 3000cc for between 5-8.0 psi boost. Two drive ratios were used 0.8:1 and 1:1 depending on the power required. An RO20 supercharger fitted to a 1300cc engine with a drive ratio of 1:1.0 will supply a maximum boost of up to 18 psi. The RO20 weighs 40 lbs. The maximum rotor speed is

6,500 rpm; for continuous use 6,000 rpm. The RO34 is a longer RO20, with displacement per revolution of 3400cc for engines from 3000 to 5000cc at 6,000 and 5,500 rpm. For more Wade information: .

Volumex

     For more Volumex information: .

Positive Displacement, Twin Screw

    These superchargers (like the twin rotor types) have two rotors turning in opposite directions. The rotors are multi-lobed helix, and are generally driven by counter-rotating gears inside the front housing. Each rotor is radially symmetrical, but laterally asymmetrical.
    These are true superchargers. The male rotor has three lobes, the female five lobes (females in earlier designs had four). The intake charge is drawn in at the end of the rotors in the large clearance between the male and female lobes. At the intake end the male lobe is much smaller than its female counterpart, but the relative sizes reverse proportions along the lengths of both rotors (the male becomes larger and the female smaller) until (tangential to the discharge port) the clearance space between each pair of lobes is much smaller. This reduction in volume causes compression of the charge before being discharged into the intake manifold.
    The overdrive ratio between the engine and this supercharger type varies between 1:2 and 1:4, depending on the exact model and application, and always limited by the manufacturer’s maximum RPM limit.

Opcon Autorotor

    This is the oldest true compressor, also known as an “axial flow” compressor, which was developed by Svenska Rotor Maskiner (SRM) in 1936. Alf Lysholm was the design engineer. It reduces the volume of the intake charge internally. Manufactured under license by IHI for Mazda, and for Sprintex, PSI, Whipple, &c. For more Opcon Autorotor supercharger information: .