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Judson Supercharger Rebuild for the “Georgia Peach” Volvo 122s

Since the last report on the 1968 Volvo 122s a few weeks ago, there has not been any spare time to do much to it other than to make some brake adjustments and get it registered. With any mechanical rebuild or restoration parts need to be located and purchased and with the use of the internet, and some occasional late night searching and emailing the many of the needed parts have been found.

Two months ago I was able to contact George Folchi, a machinist, who rebuilds Judson Superchargers in his spare time, and also supplies new old stock Ampco engine top end lubricators. George provided a new set new micarta vanes for the aluminum rotor that are visible in the lead photo and below set in the rotor slots. He machines them from micarta stock, the same material used for the originals; it is a strong and long wearing thermosetting plastic and cloth composite that is the same material that was used for “fiber” camshaft gears for decades.

Judson Supercharger Rotor and Vanes

  • The slots visible above assist in collecting oil mist from the top end lubricator for the rotor slots and the sides and tips of the vanes.

If you return to the lead photo, the rotor and vanes are mocked up in about the same position in the housing bore that they rotate in with more a bit more clearance provided below the assembly. The assembly spins clockwise, and the vane on the far-right is shown at about five degrees before it begins to admit the fuel and air charge fed by the carburetor and the intake manifold at atmospheric pressure. It passes into the back side of the bottom half of the blower housing visible below and through to the inside via the diamond shaped openings at the bottom.

After the intake charge enters the blower housing, it is then compressed into the very small area under the rotor. If you follow the rotation sequence, the vane then begins emerge out of the rotor slot aided by centrifugal force and continues to rotate while the mixture is being compressed. The pressurized mix (5-7 psi) is then forced out of the blower housing through openings in its bore into the divided passage seen below at the top and into the intake manifold. Once into the plenum the compressed mixture enters a pair of intake runners and continues on to the ports in the cylinder head.


  • The passageways on the backside of the supercharger housing that admit and discharge the fuel, oil and air mix.

A new old stock Ampco “Vapor Lubricator” seen below supplied by George Folchi will be used instead of the “Marvel Mystery” Oiler that Judson originally used with these units. The Ampco is a better design and will supply “Marvel Mystery Oil” through a spray nozzle into the top of the carburetor throat in the amount of about one drop very two-four seconds. After lubricating the blower housing and vanes, it passes into the cylinder head and serves as a top end lubricant for the engine. A quart of the fluid is needed every five to one-thousand miles depending on how it is used and adjusted.

After the rest of the maintenance and repairs needed for the car are finished up, this rebuild will be covered here. If things go smoothly, and I can find the time, the supercharger might be finished up and installed this fall.

View the earlier parts of this series here.

  • The new old stock Ampco “Auxiliary Lubricator,” installation kit and the original instructions.



18 responses to “Judson Supercharger Rebuild for the “Georgia Peach” Volvo 122s

    • Yes, my favorite brand of milling machine vice and it’s in there bolted to a piece of left over aluminum plate because the mill will not be needed for a while.

      Do you do some machining?

  1. Good ‘ole Sears/Allstate aftermarket items. Dave, the wood drawers on your work bench looks very unique.

  2. Back in the last century I had a job at a Philadelphia quasi-experimental shop that was working on a ”flying geep”. Two large rotors, powered by a pair of Franklin 6 cyl aircraft engines. When ready for ”flight” the thing wouldn’t get off the ground. ”More horsepower” was the cry” –if you put enough horsepower on any thing, it will fly. Judson was in a Philadelphia subburb, and the Engineering guys went to see him. He offered a pair of blowers meant for fllathead Ford V8’s, on trial, probably after plenty of smoke was blown his way about how he would be the supplier of choice once the Government was convinced into ordering a fleet of these things. The engineers left with the blowers,and a stern warning as to not exceed a certain RPM.

    Pulleys were made up for the noses of the Franklin cranks, belts procured, and it was Showtime again. Results this time were more promising, as the craft hopped and teetered on two of it’s three wheels. ”More horsepower! Larger crank pulleys! Flight tests were conducted in the afternoon and they wanted to try again the next day, weather permitting. Drawings were made, stock cut and second shift started machining. Two of us were on third shift then and when I came to work at 11:30 PM I was told that come morning I better have 2 pulleys for the flight test crew to install–NO EXCUSES! I finished them up, and gave them to the FT foreman when he arrived.

    Much better results this time, the thing would scoot around on ground effects ( the result of the air from the props hitting the ground–requires less HP than actual flight)–but strange things were happening also–exhaust valves were starting to burn out. Read the previous paragraph again.

    When I presented the third set I asked the foreman if they had made any changes to the ignition timing and mixture, and I was told that there was no reason to do so. Hot Rod magazine was my bible at this time and I knew that these changes were very important, but don’t argue with the boss! Read that paragraph again–better results this time, but still probably within ground effects.

    Set number 4 ordered, and delivered–but this time all12 exhaust valves were shot after 20 minutes flight time, and funny little things were mysteriously gnawing at the piston heads.
    test 4 flight time only lasted about 5 min, as I recall, but success was just around the corner.

    Please read the paragraph again, The weekend was coming up fast, and I probably was afraid that they would want me to come in Saturday night–I had better things to do. There was a box of blown up aluminum parts this time–I guess that the red line for the blowers had been exceeded by a large margin. the pieces were handed back to Judson, and I heard that he was told that the blowers were totally unsatisfactory.

    Flight–such at it was —- was achieved with a French turbine of, I think, 600 HP But the thing was useless on the ground–and it was supposed to be an all-purpose machine.

  3. Quote “The assembly spins clockwise………..” From which viewpoint ?
    As seen in the lead photo, surely, spinning clockwise wouldn’t throw the Mica blades out of their slots, to rub against the outer wall, since they are at such an angle as to resist the centrifugal force.
    I take it that their purpose is twofold, to collect air, AND oil mist on the walls ?
    Or is there some other reason I’m missing ?

    • It spins clockwise as viewed in the lead photo.

      If you look at the top vane in the photo, it is at a 45 degree angle to the center shaft and centrifugal force indeed does force it out, but at only half the force it would if it was at a right angle to the shaft.

      This configuration was chosen to cut down on wear to the vane tips.

    • Probably because back in this period oilers like the Ampco and Marvel Mystery where used to do top end lubrication and on its way into the engine this case it oiled the supercharger.

  4. Wow,I didn’t think micarta would be able to stand up to that kind of wear.
    It must come available in different grades nowadays.

  5. Is it possible to use a Judson meant for a 1955 + VW on my Ford Flathead V8 60 HP 136 cu in motor? For street use and a little added fun and the fun of adapting it to the 60. Maybe for some WOW, too?

  6. Hi David, thanks for the article, great read.

    I was wondering if the vanes had oil channels on both sides, I can only see the trailing sides in the pictures.

    Have you ever tried to raise the boost over 5 psi?

    Asking because I like to dabble, I might try to make one, been interested in them ever since I saw my first anti-pollution pumps in the mid 70’s on many cars.

    • Oh, and also, about where does the air inlet start drawing, it looks like 10 or 11 o’clock in the lead picture, but clearly expansion is taking place by 8 o’clock, is there grooves around the bore to at least 9 o’clock?

      Thanks 🙂

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