Judson Supercharger Installation Instructions MkI-MKII Sprite & MK I Midget


The following is reproduced from page 228-238 of Floyd Clymer's Sprite-MG Midget Owners Handbook of Maintenance and Repair published 1962. The copyright is held by Judson Co., and is used with permission. The information contained below may be helpful if you plan on installing a Judson Supercharger. They do come up on ebay occasionally. At the vary least it will help you get an idea of what parts are needed and what is involved in the final installation. Never attempt this installation without first rebuilding the Judson supercharger (and collecting all the needed parts). Remember that the advice given in the article is based upon brand new parts and a brand new car (and the fuel available back in 1962). Since you may be working with 50 year old parts on a 50 year old car, and running it with You may need to rebuild your engine with a supercharger in mind before attempting this.


To realize a decent increase in power without going into a disassembly process, but by spending a moderate amount of money ($169.50) the application of a low-pressure supercharger seems to be the answer. The Judson, a rotary vane type delivering about 6 Ibs. of boost at maximum, has an excellent record for reliability and service. It raises horsepower to approximately 65 hp on the 46 hp engine. Blown engines, on the whole, are no less dependable than unblown and require no more maintenance other than checking the oil level in the lubricator. Since consumption of lubricant is approximately 1 quart every 800 to 1,000 miles, this imposes no hardship on the owner who gives nominal attention to his engine.

To give a rather complete idea of the normal supercharger installation, or for the benefit of the Sprite owner who may purchase a used blower unit, we are including a step-by-step description of the fitting sequence,

  1. Disconnect gas line, vacuum advance line, choke control and throttle control from carburetors. Remove carburetors, heat shield and intake manifold from engine. Replace original heat shield bolt that clamps breather tube to crankcase. Remove gas line completely by disconnecting from fuel pump. (See Fuel System Section.)
  2. Remove radiator.
  3. Unscrew bolt from end of crankshaft located in center of crankshaft pulley. To remove this bolt it is necessary to straighten the locking washer under the head of the bolt so that the bolt can turn. If bolt is too tight to remove by wrench, it can be broken loose by using a chisel on the side of the hex. Original crankshaft pulley is not removed from the engine.
  1. Place aluminum crankshaft pulley furnished with supercharger kit on front of original pulley making sure that shoulder is inserted in bore of original pulley and rivets line up with holes in aluminum pulley. Replace original flat lockwasher and bolt on crankshaft. Rebend one side of flat locking washer against bolt head and punch other side of washer into hole of aluminum pulley. This locks bolt on crankshaft.
  2. Replace radiator.
  3. The flexible fuel line is installed by removing the fuel pump end of the original fuel line as shown in the sketch below. This short section of the original fuel line is then inserted approximately 1" into the flexible gas line furnished and clamped with one of the hose clamps removed from the original carburetor hose.
  1. Place lubricator in position as shown in photo. Container should rest against throttle tube support and brake cylinder angle. Use mounting plate on bottom of lubricator as template and drill two 1/8" holes. Fasten lubricator with two self tapping screws furnished with kit.
  1. Remove original throttle cable clamp from the SU carburetor throttle bar and insert in the throttle arm of the carburetor furnished with kit. Insert throttle cable clamp through in side hole as shown in photo. One washer goes between hex and throttle arm and two washers between throttle arm and cotter pin.
  1. Fasten supercharger to engine using original nuts and washers that held manifold to engine . Make sure that center support bolt is backed off free of exhaust manifold plate before tightening nuts securely. Screw down center support bolt until resting on exhaust manifold with just enough ten sion to support supercharger but not enough to pry on manifold. Lock center support bolt in position with nut.
  2. Fasten heater tube with one original clamp as shown in photo. Use original bolt and washer.
  3. To install front support brace, remove nut and washer from upper stud on rubber engine mount. Place end of brace with hole on stud. Replace washer and nut firmly on engine support but do not tighten.
  4. Remove loose bolt with washer from front of supercharger and place through slotted end of support brace.
  5. Fasten front support securely by tightening nut on engine support stud and bolt on supercharger.
  6. Re-position water hose by using wire clip around support brace and hose as shown in photo. This prevents belt from rubbing on hose.
  1. Remove 5" from carburetor end of original vacuum advance line. This should be done by scoring tube with file and breaking (culling with cutters will close hole). Insert original vacuum advance line into hose on end of extension furnished with kit. Original line should be inserted in hose as far as possible. Remove small tube fitting from vacuum connection on carburetor, insert on copper line and connect to carburetor pushing tube into carburetor connection as far as possible.
  2. Bend fuel line as shown in photo and connect to carburetor. Tighten fitting on carburetor and fuel pump.
  3. Connect choke wire to carburetor making sure that the choke button is pushed in completely on the dash panel and that the choke butterfly on the carburetor is fully open. Choke sheath is clamped on carburetor as shown. Choke wire goes through brass fitting on carburetor and is clamped by screw. Friction tape should be wrapped around the choke sheath where it passes over the wind shield wiper motor. This will insulate the choke control from the wind shield wiper motor wire terminal.
  4. Push throttle cable through extension bolt on rear of supercharger. Feed cable through origin al clamp that has been inserted on carburetor arm. Pull cable down making sure sheath is securely bottomed in fitting below lubricator and in extension bolt on back of supercharger. Before tightening clamp for throttle cable, bend cable assembly down flat against fender. Tighten clamp on carburetor. If cable is not bent down against fender before tightening clamp, the engine will speed up when hood is closed.
  5. Connect oil line to lubricator and to the fitting on the intake manifold directly under the carburetor.
  1. Drop idler bracket down by loosening clamping bolt until idler pulley rests on shock absorber.
  2. Place belt over crankshaft pulley and pulley on supercharger. Pull idler pulley tightly against belt and tighten clamping bolt on idler bracket making sure that idler pulley is in line with the other two pulleys and that the idler bracket is not in contact with pulley on supercharger.
  3. Bend fan blades forward slightly until there is 5/16" to 3/8" clearance between blades and supercharger belt.
  4. Place air cleaner on carburetor and fasten original hose from valve cover to connect ion on air cleaner using original clamp. Secure air cleaner to carburetor by tightening clamp on bottom of air cleaner with screwdriver.
  5. Refill radiator.
  6. Fill the automatic lubricator with No. 10 HD (detergent) motor oil. The engine must not be started unless the lubricator is connected and filled with oil. The lubricator tank has a capacity of 1 1/2 qts.
  7. Fill float chamber of carburetor by pumping lever on side of fuel pump and start the engine. As soon as the engine is running, adjust the lubricator as per instructions under lubrication. After engine is warm, set idle mixture on carburetor. Adjust back and forth until a smooth idle is obtained. The idle speed adjustment screw is spring loaded and located on the throttle arm of the carburetor. With pliers set idle speed at approximately 800 RPM.


Valve Clearance

The stock valve is recommended. Check to make sure that both intake and exhaust valves have a clearance of .012.

Head Bolts

Tightness of head bolts should be checked to 40 ft. Ibs. starting from center bolts and working out.

Spark Plugs

Remove the spark plugs and examine for wear and corrosion. If spark plugs are not in good condition t hey should be replaced. Use Champion N·5 spark plug, ga pped at .020 to .022. Tighten to 30 ft.Ibs.

Ignition Point Setting

Stock gap of .014 to .016 is recommended (54 to 57 degrees If set with cam dwell indicator) .

Ignition Timing

The stock ignition timing setting of 5 degrees before top dead center is recommended. If additional retard is required because of available fuel or carbon deposits, it can be obtained with the knurled screw on the side of the distributor.


The carburetor furnished with the supercharger has fixed jets and has been specifically set up for the supercharged Sprite. It provides the correct fuel -air ratio throughout the entire speed range of the engine. The only adjustment provided for on this carburetor is for the idle mixture and idle speed.

A flat spot will be encountered at slow speeds or on acceleration if the idle mixture is too lean. The idle adjusting needle valve (brass screw) should be unscrewed until engine slows down appreciably, then the throttle adjusting screw screwed in to provide correct idle speed.


Lubricator Adjustment

(Lubrication is very important). To adjust the lubricator proceed as follows: Start the engine. The small knurled knob on the very top (under protecting cap) should be unscrewed a half-turn to get the oil flowing and then adjusted with your fingers until the lubricator is putting out approximately one drop of oil every four to five seconds at idle. This can be timed through the small win dow on the lubricator. Screw clockwise to decrease the amount of oil consumption. Oil consumption should run one quart of oil every 800 to 1,000 miles and the oil level should be checked occasionally so that you do not run out of lubricant. Engine and lubricator should be warm while adjustments are being made. The adjustment should be checked after the first one hundred miles.

The oil from the automatic lubricator is to oil the bore of the supercharger housing and also acts as an upper cylinder lubricant. The two main rotor bearings of the supercharger are greased and sealed at the factory. Use any good grade of SAE No. 10 detergent motor oil. Do not use an upper cylinder lubricant as most top oils are primarily a cleaner and not a lubricant. Do not use a multiple viscosity oil. In making a long descent from high altitudes it is advisable to open the throttle occasionally to insure adequate lubrication because of the high vacuum. The lubricator should be adjusted and left alone as any variance that will occur at idle will be slight under actual operation and is averaged out over the vacuum range of the engine.


Premium grade or high octane gasoline is recommended on the supercharged engine. Super premium fuels are not necessary.


No breaking-in-period is required for the Judson Supercharger. We do, however, recommend that the engine be run slowly or at idle for at least fifteen minutes before placing the engine or supercharger under load.


The supercharger may sound noisy when it is first started or with in the first half hour of operation . This noise is nothing to be concerned about and will disappear completely with in the first 20 to 40 miles of hard driving. A slight clicking noise sometimes at idle or after backing off of the throttle after a hard run is characteristic of a vane type supercharger.

Belt Replacement

In case of drive belt breakage the supercharger will cease functioning but the engine will continue to operate. The drive belt is a standard size and can be purchased from any automotive jobber under Gates number 8209 or from your Chevrolet dealer and is the same belt as used on the Chevrolet 6 cylinder (1955-1956. w/H.D.


Because the supercharger is scavenging the hot gasses from the cylinders, the Sprite engine has a tendency to operate colder when supercharged. In cold climates we recommend replacing the 164 degree water thermostat with a 180 degree water thermostat. This replacement water thermostat can be purchased at your local Chevrolet dealer as Water Thermostat No. 3133698, Type 108, 180 degrees.

As on the unsupercharged Sprite, a section of the radiator should be blocked off in freezing temperatures in order to raise the temperature of the engine compartment and the temperature of the charge entering the carburetor. A flat spot will be encountered on acceleration if the water temperature or the temperature of the air in the engine.compartment is too low.

Supercharger Pressure

A supercharger gauge is available as an accessory for the Judson Supercharger. Gauge matches other instruments on Sprite dash panel and reads both manifold vacuum and pressure. The Judson Supercharger replaces the vacuum in the manifold with a pressure in proportion to the load placed on the engine. There is always a vacuum in the manifold when the engine is at idle or when the engine is not under load. The vacuum in the manifold is replaced with a pressure as the throttle is opened and the engine is placed under load. Highest boost pressures are obtained under full throttle operation when accelerating or going up an incline. Pressure will vary according to condition of engine, altitude, speed, humidity and engine load. Maximum manifold pressure, because of these conditions, will vary between 5 to 7 pounds. Even when the engine is not operating with a manifold pressure at idle or when there is no load on the engine, the efficiency of the engine has been increased due to the improvement in volumetric efficiency. There is a direct relationship between fuel consumption and manifold boost pressure as the horsepower available increases with the boost pressure. When you do not use the additional power afforded by the supercharger by pushing the engine, you do not pay for it through increased fuel consumption.


Installation of Supercharger

It is very important that the instructions be followed exactly in installing the supercharger on the engine. Mistakes usually made: throttle cable improperly adjusted not allowing throttle on carburetor to open or close completely. Sheath for throttle cable must be seated in extension bolt on back of supercharger and also seated in chassis fitting below lubricator. The throttle on the carburetor must be completely open when the accelerator pedal is fully depressed. Choke butterfly in throat of carburetor should be fully open when choke button on dash panel is pushed in completely. If center support bolt located on supercharger manifold is screwed in too far it will pry the manifold away from the side of the engine causing a leak resulting in a rough idle and poor performance. Support bolt should be tight enough to support the weight of the supercharger.


Maximum performance after supercharging is a function of engine condition and tuning. Engine deficiencies often unnoticed before supercharging sometimes prevent the increased performance that can be expected from the supercharged engine. Because of this the supercharger will often be blamed for poor performance when such is not the case. If the installation has been made in accordance with the instructions and the performance is poor it is usually due to a leak in the induction system, improper valve clearance or a faulty ignition system.

The ignition system on the supercharged engine should be in good condition and properly adjusted, incorrect timing and point setting as well as faulty plugs or ignition wiring affects performance considerably and contributes to poor performance. See installation data for timing, point and plug setting. If poor performance cannot be attributed to any of the above after a thorough checking it can be assumed that the trouble is of an internal mechanical nature and the engine itself should be checked by a competent mechanic. Best performance for dependability is obtained from the stock engine. We do not recommend increasing the compression ratio, the use of a special cam or making any other basic modifications on the supercharged engine.