VS57 Operation

I apologize for the blatant use of the Kaiser Supercharger manual in constructing this description of the VS57 operation. The descriptions given in both the Kaiser manual and the VS57S manual produced by McCulloch are exactly the same, and both are very good and easy to follow, so I thought I might just as well use those descriptions, rather than create my own which probably would be difficult to understand.  I’ve noted the differences between the Kaiser, Studebaker and kit superchargers where applicable.


As with all centrifugal-type superchargers, it is necessary to drive the impeller at a very high RPM speed to obtain the required boost pressure output. This is accomplished in the McCulloch supercharger by incorporating two points of shaft speed-up in the design. The first is at the variable-ratio pulley, keyed to the input shaft, and the second point is at the planetary drive system between the input and output shafts.

When used with the standard 7-1/2 inch diameter crankshaft pulley, the variable-ratio pulley offers a 1.3 to 1 RPM increase when it is in the fully closed position. When the pulley is fully opened, the increase is 2.3 to 1. Thus, when the flanges are fully closed, the supercharger is operating at “low blower”. When the flanges are fully separated, the supercharger is being driven at “high blower”.

Movement of the rear, or sliding flange of the pulley is automatically controlled by the functioning of the control system. Operation and function of the control system is explained later.

The belt-tensioning arm, and idler pulley, apply pressure against the drive belt and cause the belt to pull down into the pulley and separate the flanges during the shifting cycle from “low” to “high” blower.

The planetary drive system, incorporated between the input and output shafts, is the second point of RPM step-up. The ratio of the system is a constant 1 to 4.44 and does not vary under any operating conditions. When the supercharger is in “low blower”, the impellor is turning approximately 5.7 times as fast as the crankshaft (1 x 1.3 x 4.44). In “high blower”, the impellor is being driven approximately 10 times faster than the crankshaft (1 x 2.3 x 4.44). However, when the supercharger is in “high blower” and the engine is turning at high RPM, the regulating action of the control system limits the boost output to a predetermined level.

The control system regulates the boost output of the supercharger by governing the movement of the sliding flange of the variable-ratio pulley. Simply, the control system is a solenoid operated valve that controls the passage of boost pressure, taken from the discharge throat of the supercharger, into an air chamber. Within the air chamber is an air piston which is coupled to the sliding flange of the variable-ratio pulley through a thrust type ball bearing. The full function of the system is detailed later.

Drive System

The drive system is composed of the following component assemblies:

a)     Variable-ratio Input Pulley

b)     Input Shaft

c)     Planetary Drive System

d)     Output Shaft

Figure 1

Figure 1 shows the power flow through the drive system of the supercharger. (A) is the variable-ratio input pulley. The fixed flange (A-1) of the pulley is keyed to the input shaft (B) through a splined hub. The sliding flange (A-2) of the pulley is fitted with a splined bushing to permit constant drive of the input shaft through the full limit of travel of the flange. Movement of the sliding flange is controlled by an air piston (J) working in an air chamber, or cylinder.  Minimum ratio, offered to the driving pulley, exists when the two flanges are closed. Maximum ratio is presented when the sliding flange has move away from the fixed flange the full limit of it’s travel.

A ball drive (C ) is a component part of the input shaft assembly. It serves only to rotate the five drive balls (D) of the planetary system around the inner faces of the ball races (E). The clutch discs (F) prevent the ball races from turning in their respective mounts.

As the drive balls (D) revolve around the cage formed by the two races (E), they also rotate around their individual axes. This latter motion is transmitted directly to the output shaft (G), causing it to rotate. As the output shaft serves as the inner race of the planetary system, the system ratio is calculated between the inner diameter of the ball races and the raceway of the output shaft.

The impellor wheel (H) is attached to the end of the output shaft by a retaining hex-head screw.

Variable-Ratio Input Pulley

Figure 2

The component parts of the variable-ratio pulley are shown in figure 2. A socket-head cap screw, lockwasher and retainer serve to hold the overall assembly to the input shaft.

The fixed flange is internally splined to fit the splined hub which is keyed to the input shaft. The flange does not move and serves only as the working face to the sliding flange.

The sliding flange has a splined bushing insert that permits the flange to slide along the surface of the hub and still continue driving the input shaft.

A sealed, thrust-type ball bearing, fitted to the rear of the sliding flange, is used to transfer movement of an air piston to the flange to accomplish ratio shifting of the pulley.

Shifting of the variable-ratio pulley is accomplished by the combined functions of the control system, an air piston, and the belt-tensioning arm and idler pulley. The shifting is automatic, as determined by engine load conditions.

Figure 3

When the supercharger shifts from “high blower” to “low blower”, it is a result of boost pressure (taken from the discharge throat) being passed into an air chamber, or cylinder, containing the air piston. The pressure behind the piston (see figure 3) drives it forward and the movement is transmitted to the sliding flange of the pulley assembly though a ball bearing. The pressure is sufficient to overcome the tension applied to the drive belt by the belt-tensioning arm and, as the pulley flanges close, the belt is forced to the top of the pulley and the speed of the input shaft is reduced. An equalizer spring behind the piston helps to overcome the effect of the tensioning arm against the drive belt.

NOTE: During idle-speed engine operation, the drive belt and variable-ratio pulley are in the “high blower” position as there is insufficient boost pressure being developed to drive the air piston forward. As the engine speed is increased, the boost pressure out-put reaches the level required to drive the piston forward and shift the supercharger into the “low blower” range. The spring behind the air piston serves to equalize the tension exerted by the belt-tensioning arm against the drive belt, thereby holding the level of pressure (PSI) required for this function to a minimum.

During the shift cycle from “low blower”, a valve in the control system closes to prevent boost pressure from entering the air chamber. The pressure within the chamber bleeds, or vents off, and the tension on the drive belt (exerted by the belt-tensioning arm) causes the belt to pull down into the pulley and separate the two flanges.

Computed against the standard 7-1/2” diameter crankshaft pulley, the minimum ratio of the variable-ratio pulley is 1.3 to 1. The maximum ratio, when the flanges are fully separated, is 2.3 to 1.

The belt-tensioning arm, or idler arm, is mounted to the same bracket used to mount the supercharger. The spring-loaded arm is geometrically located with relation to the center line of the supercharger input shaft to apply tension, measured in pounds, to the drive belt. The existing design should not be altered in any way as it will affect the shifting cycles of the variable-ratio pulley.

Input Shaft

Figure 4

The composite input shaft assembly as shown in figure 4, is the central shaft in the drive system and is supported in the bearing housing by two ball bearings.

The oil pump assembly fits on the shaft between the two bearings. The plunger of the oil pump is actuated by a camway ground into the input shaft. A ball driver fastened to the rear of the input shaft by five screws, rotates the drive balls of the planetary drive system. A bushing, inserted in the input shaft, serves to pilot the output shaft. This bushing also has a function in the lubrication system.

The input shaft is keyed directly to the variable-ratio pulley and always turns at the RPM speed being turned by the pulley.

Planetary Drive System

Figure 5

The component parts of the friction-type planetary drive system are shown in figure 5. The ratio of the system remains constant under all conditions and is 1 to 4.44, input to output shaft.

When assembled into the supercharger, the drive balls are enclosed between and revolve around the inside faces of the two ball races. As the drive balls are turned (by the ball driver) around the races, they also revolve around their own axes. It is this revolving motion that is transmitted to drive the output shaft, as the output shaft forms the inner raceway of the planetary system. This is shown in figure 6.

Figure 6         Figure 

One ball race is fitted into the scroll housing and the second race is fitted into the collar of the race load assembly. A clutch disc is inserted behind each race to prevent the race from turning.

The race load assembly, through compression of internal springs when the supercharger is assembled, applies pressure evenly around the front ball race (see figure 7). The contact point (A) is between the race load assembly and the bearing housing. Pressure is applied to the planetary system at (B), through the clutch disc (C). As the ball race (D) is forced against the drive balls (E), the balls are pressed backward against the rear ball race and down against the raceway of the output shaft.

The design of the overall system provides for maximum drive with minimum slippage, while also providing for the take-up of any wear that might develop in the ball races or drive balls.

Output Shaft

The output shaft, as part of the drive system, is the rotating inner raceway of the planetary system. The ratio step-up of 1 to 4.44 therefore is calculated between the inner contact surface of the ball races and the outer contact surface of the output shaft.

Figure 8

A slinger ring (figure 8) is pressed on the output shaft to aid in the prevention of loss of lubricant from the lubrication system. Two labyrinth rings, fitted into grooves of the labyrinth section of the shaft, also serve to prevent loss of the lubricant.

The impellor wheel fits onto a pilot hub on the end of the output shaft and is retained by a washer, a lockwasher and a hex-head cap screw. Two dowel pins pressed into the output shaft prevent the impellor wheel from slipping on the hub during acceleration or deceleration of the supercharger.

A shim, or shims, placed between the impellor wheel and the output shaft, provide for proper clearance between the back face of the impellor wheel and the face of the scroll housing. When the shims are correctly fitted the spacing between the vanes of the impellor wheel and the internal face of the scroll cover is automatically correct.

Lubrication System

Figure 9The supercharger is self lubricating by a piston-type oil pump which works off a camway ground into the input shaft. The oil sump holds eight ounces of lubricant. Use Automatic Transmission Fluid, Ford Type A only.

NOTE: Never use any but this specified lubricant, as this lubricant is designed for high heat range applications. The use of standard automobile engine oil will result in oil breakdown and cause serious damage to the supercharger. Component parts of the oil pump are shown in figure 9. A dip-stick oil gauge, marked to show “safe” operating level and “add oil” level of the lubricant, inserts in a sleeve located in the bearing housing.

The overall lubrication system is shown in figure 10. In operation, oil pump (C ) is fitted to the input shaft and extends down into oil sump (D). Plunger (B) follows a camway (P) ground into the input shaft. Spring (E) keeps the plunger in constant contact with the cam. As the plunger follows the low portion of the camway, oil is sucked through oil passageway (F) and enters the chamber just at the bottom of the plunger. As the plunger is pushed down, the oil passageway is sealed off and the oil trapped in the lower chamber is compressed and forced up the hollow stem of the plunger.

NOTE: the small ball (G) is not a check ball, but serves only to seal the drill passage where it enters the body casting of the oil pump.

As the oil enters chamber (A), pressure is built up by the escape limitation imposed by clearance (O) existing between the insert bushing and the pilot boss of the output shaft. Thus, oil is forced out of the chamber in the direction of arrows (M), and sprayed on the planetary system drive balls. Slinger (L) and labyrinth rings (K) prevent loss of lubricant into the diffuser section of the supercharger.

The spray of oil falls into the forward section of the oil sump (J). There, small holes (H) around the face of the race load assembly permit the oil to seek it’s own level within the sump. Ball bearings (N and Q) are lubricated by the existing oil spray and seepage of oil under the bushing of the oil pump. Shaft seal ® prevents large quantities of oil from entering the front section of the supercharger and also serves to keep dirt out of the lubricating system. However, a small quantity of oil passes under and around spacer (S) to provide lubrication for the air chamber and air piston.

NOTE: the thrust-type ball bearing which joins the air piston and sliding flange of the variable-ratio pulley is pre-lubricated and sealed and does not require additional lubrication.

Control System

The control system of the McCulloch supercharger regulates the output of the supercharger by controlling the movement of the sliding flange of the variable-ratio pulley. In effect, the system is an electrically operated valve which controls the passage of the boost pressure, taken from the discharge throat, into an air chamber. A piston within the chamber is coupled directly to the sliding flange of the pulley through a thrust-type ball bearing.

The main electrical component of the system is a solenoid regulator which is energized by the closing of an external switch. Located in the bearing housing, the regulator intersects an air passage leading between the discharge throat and the air chamber. The external switch, for the Kaiser and Studebaker, is a kick-down type switch mounted on the carburetor enclosure and operated by the throttle linkage, and for all other applications, is a vacuum switch bolted to the supercharger, and driven by manifold vacuum.

The solenoid regulator has three phases of operation, as shown in figure 12.

Figure 12 (Whatever happened to 11?)

Phase “A” – The solenoid regulator is not energized and the valve is open, permitting boost pressure to enter the air chamber. The air piston is driven forward, closing the variable-ratio pulley and the supercharger is operating in “low blower”. Minimum horsepower is required to drive the supercharger during this phase, as the supercharger is not producing high level output. This phase extends across the cruising range of the engine, where the engine does not demand, and cannot use, boost pressure. Under acceleration or full load demand of the engine, the supercharger shifts into Phase “B” operation.

NOTE: Phase “B” operation is initiated when the accelerator is depressed sufficiently to either cause the throttle linkage to close the contacts of the kick-down switch, for the Kaiser’s and Studebakers, or the engine RPM increase as a result of throttle demand, and subsequent manifold vacuum drop, causes the vacuum switch contacts to close for those systems equipped with the vacuum switch.

Phase “B” – As soon as the solenoid regulator is energized, the armature lifts and seals against the valve stem to block the passage of boost pressure to the air chamber. When the source of constant pressure is removed from behind the air piston, the pressure that exists in the chamber vents off. This permits the tension exerted against the drive belt by the belt-tensioning arm to pull the belt down into the variable-ratio pulley and move the sliding flange backward, driving the air piston back into the air chamber. The supercharger is now in the “high blower” range of operation and the boost pressure output, in PSI, is increased. As the engine speed increases under full throttle, the boost pressure output also continues to increase until it reaches a pre-determined level, as based upon that which the engine can safely use. At this time the solenoid regulator enters Phase “C” operation, to regulate the output of the supercharger.

Phase “C” – The design of the supercharger and drive system is such that maximum boost pressure output is produced at a crankshaft speed below maximum engine RPM. This permits production of usable boost pressure at lower engine speeds and also increases the range of engine speeds over which usable boost pressure is produced. However, if maximum output is produced at a mid-range speed of the engine, it is obvious that pressure output would continue to increase as the engine speed increases to maximum RPM. Therefore, it is necessary to regulate the pressure output, in PSI, to a level that is compatible with engine design and available fuel.

This is accomplished by a diaphragm located within the solenoid regulator case. A spring on the top side of the diaphragm is adjustable and the change of spring rate determines the pressure, in PSI, required to distend and lift the diaphragm. As the diaphragm is positioned against the head of the valve, any upward movement permits the valve to lift off the seat formed by the armature. It is this function that forms the Phase “C” operation of the solenoid regulator. The mechanical operation is as follows:

During “high blower” operation, the solenoid is energized and the armature has moved upward to seal the passage of pressure into the air chamber behind the air piston. As the engine speed continues to increase and the boost pressure output reaches the level for which the diaphragm spring has been pre-set, namely four PSI for the Kaiser and five PSI for other applications, any pressure gain over the pre-set value will cause the diaphragm to distend. This permits the valve to lift off the seat to the same degree and open the passageway to the air chamber to allow boost pressure to enter the chamber. As the equalizing spring behind the air piston is compressed, neutralizing the tension exerted by the belt-tensioning arm, the small amount of pressure passing the partially opened valve is sufficient to cause the air piston to move forward. This action, in turn, causes the sliding flange of the pulley to move forward and reduce the working diameter of the pulley. As the ratio changes, the input shaft speed is reduced, the impellor wheel slows down and the boost output pressure returns to the regulated level.

At this point, with the valve still partially opened and the pulley semi-closed, any increase in engine speed will also increase the boost pressure output. This will reflect in greater distension of the diaphragm and a larger opening in the passageway as the valve stem follows the diaphragm. A still greater volume of boost pressure is permitted to enter the air chamber to again drive the sliding flange forward to reduce the ratio of the driven pulley.

This regulating action continues through the high end of the engine speed curve until the full limitation of the diaphragm has been reached. However, the overall design of the supercharger and control system is such that the limit of regulation holds very close to the maximum usable engine RPM.