The Sprite Forum

The way the vanes sit in the "swastika cut" slots in the rotor of the Judson is such that they are sufficiently out of the way when the rotor is not turning and allow the car to run normally aspirated. It's not the most optimal air flow but it works.

I once drove from Philadelphia to Carlisle, PA in this configuration.

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Specialization is for insects.

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Specialization is for insects.

Dean,
Thanks.
Phil.

So a little update, I went for a little run yesterday and once warmed up it ran fine for about twenty minutes or so and then started to stumble and misfire until I gave it some hard throttle and back off a few times. It would run ok for a bit then do it all over again. When I got home I pulled the plugs and they were very black, dry and black. So I'm rich. I talked to George Folchi and he suggested the float level and that the carb should have a #62 jet. I'm about to pull the carb and I'll let you know what I find. David

I'm old enough to remember all the Judson ads from when they were new and sold at JC Whitney. I also remember tales of driveability problems with them and when I was looking to upgrade the performance of my 948 in the 80s I went the more conventional route of HS2s, 18G 295 head, 88G 229 cam, LCB header, etc to get to a whopping 55 bhp, which was about what the Judson advertisements touted. It runs great, with no driveability issues. Are the Judson owners happy with their decision, or would they choose a different route? They still look very cool under the bonnet and that has to be worth a lot.

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Rick

"Madman in a death machine"
Austin-Healey 3000 w/5.0L and T5Z: http://forum.britishv8.org/read.php?13,8264

I pulled the carb today and dismantled. The float level was way off so I fixed that. The jet was the correct #62. I will run into town tomorrow and then check the plugs again. This motor is 1380 and pulls like a race horse. There was a custom crank pulley turned for it so I'm guessing it is only boosting around 4 pounds.

I toast your efforts. Good luck.

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Rick

"Madman in a death machine"
Austin-Healey 3000 w/5.0L and T5Z: http://forum.britishv8.org/read.php?13,8264

Hi David

I don't have a Judson supercharger but I do Have an Eaton on my 1275 frogeye.
I have an SU carb on my system and after having the car tuned by a specialist on a rolling road I had exactly the same problem as you.
When cold the car wanted to stall unless the engine was constantly revved or the car run fast. When it was warmed up the car ran beautifully and pulled like a train.
The solution was in the setting of the mixture and choke. By trial and error I managed get the settings just right, from memory the mixture was just too lean and the choke was not completely open when the knob was all the way in.
It was a real trial and error job but was limited to the choke/slow running areas.
Dont know if this is of any help.
rgds
Roger

Well Roger anything helps. Dean Hedin in the US has some great info and also uses a SU carb. He pointed out some real flaws in the judson manifold that could be improved upon. It is pouring rain right now so my next run is on hold. I guess I will have to finish the brackets for my driving lights. Cheers David

just had another question. The plugs i have right now are NGK BPR7ES, are these plugs to cold? Any thoughts.

I think you would find that the 55hp from a Judson vs. 55hp via 12G295,LCB etc. is non comparable.
Horsepower is not a good way to compare motors.

It's really about the area under the torque curve. So with the Judson, when you stomp on it you instantly have 4.5-5psi - at any rpm.
In the case of your more conventional mods, the HP figure is peaky and at a narrow rpm range.

I ran the Judson on a 948 with a Tri header, and a lightened flywheel. Under optimal conditions it felt stronger than a 1275.

The main issue with the Judson is the heat problem that I mentioned previously. It's manageable, but irritating.

I thought about installing my Judson on my now current 1275 motor. But I was a little uncomfortable of spinning it 30% faster for the 1275.

If performance is the ultimate goal, then I think a better approach for the larger motors would be the AMR500 roots type superchargers that are available for very little money up on ebay, Of course you will have to fabricate manifolds in this case.

Judsons are expensive because they are period performance items. They are rare and unique, like the Shorrock. But there are reasons why we no longer see vane type superchargers in the modern automotive world.

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Specialization is for insects.

Thanks for the reply, Dean. Very interesting.

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Rick

"Madman in a death machine"
Austin-Healey 3000 w/5.0L and T5Z: http://forum.britishv8.org/read.php?13,8264

Here is a 1380 Mini with the AMR500. Looks like a "blow through" configuration. Not sure if the AMR500 can be used in a "suck through" configuration.

One thing I notice about the AMR500 is that since having only two lobes on it's impellers it has that "buzz saw" sound to it.

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Specialization is for insects.



Edited 1 time(s). Last edit at 2022-06-16 09:28 PM by 59undine.

That was very interesting, I may have to buy one of those, just in case. David

Finally stopped raining so I hit the highway and had the same issues of stumbling after running at steady speed for a while. Pulled the plugs and they are definitely over rich. I have the recommended jet installed. Should I try smaller jet if I can get one.