The Sprite Forum

Hoping any judson drivers out there can enlighten me a bit. I have few miles on it yet but it is really hard to keep running until it is right up to temp. I have to jockey the choke and the throttle together to keep it going. Once warm it pulls strongly and idles around a 1000rpm. On the road it also seems to load up once in a while and I need to give it a strong blast of throttle to clear it up. Motor is brand new and was built specifically for this supercharger. Any advice welcome. I ask because the people on this forum know everything. David

If ya can track down Mike Owen, he will set thing straight for ya.

Who is Mike Owen?

https://g.co/kgs/uzKung

Mike Owen Auto Ltd, Sydney BC

Mike has worked on British cars for many years and his some shares the passion of buying and selling them.

If he cannot figure things out for ya not sure who could!

I suspected you might be close by. I bought a Bugeye off of him many many years ago. Sorry just realized you are not close to Sydney! I use to live on the island and there was a area called the same as your address!!!

He would take a call no doubt!

Hope it works out for ya!



Edited 2 time(s). Last edit at 2022-04-30 02:46 PM by masonr1959.

Thanks, David

Still like to hear from any judson drivers out there...

While not a Judson, my eaton supercharged 1275 has similar characteristics. My understanding is that when the blower case is cold the fuel tends to condense on the case sides taking fuel out of suspension, when the case warms up that no longer occurs and the air/fuel ratio gets back to correct. Seems that this is typical of draw through supercharger set ups.

Thank you Doug, that is the kind or real world info I was hoping for. It does make to me as the supercharger body is quite a large lump of metal. I bought this car a year ago as a driver unfortunately last year we were surrounded by smoke and wildfires and I did no driving. The motor is freshly rebuilt at a dollar more shop, all the best stuff and supposedly built as a supercharged motor.

I have quite a bit of Judson experience. By "loading up" I believe you are referring to the problem of fuel puddling in the manifold at low rpm. You then have to "open it up" to clear that fuel out. Correct?

This issue is a design flaw with the stock manifold of the Judson. The manifold starts at a small opening where the carburetor mounts and then the cross sectional area expands as it proceeds towards the Supercharger. This rapid expansion causes cooling which then causes the fuel to condensate/separate in the manifold and then collects under the supercharger. The interface at the supercharger is also not "smooth"

You can confirm this by starting it up and letting it sit and idle for a while and feel the coldness of the manifold.

The best fix is to make a new manifold (with constant cross sectional area) and mount an HS4 SU. Which is what I did.

I'll see if I can post a picture of my SU manifold here.

If you want to stick with the stock manifold then I thought it might be possible to weld a "ramp plate" on the inside of the manifold where it enters into the supercharger.

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Specialization is for insects.

OK, so here is the SU manifold that I made for the Judson. As you can see it just "sweeps right up" into the bottom of the Supercharger.
There was never any puddling/load up of fuel with this setup.

The manifold was made out of a exhaust bend. Under the supercharger the pipe was split at the top and then unbent flared outward and welded to a 1/4" steel mounting plate. and end cap and gaps were filled with addition steel sheet. It was a combination of welding and brazing. It was a bit of work.

If I were to do it again today I would probably TIG weld it using stainless exhaust pipe.

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Specialization is for insects.



Edited 2 time(s). Last edit at 2022-05-21 09:53 AM by 59undine.

Now, here is is the original Judson manifold and my proposed modification.

As you can see in the first photo there are cavities between the mounting bosses where the bolts go through.
It is a totally non-smooth interface going into the supercharger. So the airflow is turbulent.

In the second photo I mocked up with cardboard showing how I would modify the manifold to smooth the flow and eliminate the fuel puddling.
I would fill the area on the sides by welding two 1/8th or 3/16th pieces of aluminum. After these are in place I would then weld in a ramp plate on the far side.
The goal being to smooth the air flow and leave no place for the fuel to linger.

I never did this because the SU setup worked so well. But I always wanted the stock look of the single barrel Holley. The Holley actually worked pretty good were it not for this fuel separation issue in the manifold.

Anyhow this is my two cents on the issue. I can't guarantee what I propose will resolve the issue because I haven't actually performed the experiment.
I am going by my experience and success with the SU setup as guidance in this approach.

Good luck and let us know how you make out.

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Specialization is for insects.



Edited 2 time(s). Last edit at 2022-05-21 09:44 AM by 59undine.

Thank you Dean. What great info and the pictures are wonderful. Really gives me a lot of fuel for thought here. Once the bug is warmed up it runs quite well so I'm driving it this summer and may look for an SU. (I do like SU's) Then again come fall I may try your plenum fix that looks easily done. I will post updates as they happen but thanks again for the detailed info. David

I might as well provide a couple other Judson tips.

Synthetic two stroke oil can be used as a lubricant in lieu of conventional oil in the lubricator. Burns cleaner and won't compromise octane as much. Some motorcycle two stroke oils even have octane boosters incorporated.

Run as high octane as possible. This supercharger was developed in the early 60's when "high test" really meant something,

The unit runs hot...especially when it gets above 90F ambient. Hence the need for high octane. The reason fuel puddling goes away after running a while is because the unit then starts heating the manifold. It would be wise for you to install a temperature gauge to monitor the unit's housing temperature.

On hot days the housing can go over 185F.

Most think that the unit runs hot due to blade friction. This is not the case. It gets hot because it compresses the air internally.
A Roots type blower builds up pressure by pumping against back pressure in the post manifold. That is not how the Judson works.
This is easily provable as the unit runs fine at 70F ambient, but temps skyrocket when ambient goes above 90F. Flip side is that a vane type supercharger is more efficient.

The high temperatures can be managed with water injection, with a concordant increase in power output. A simple system of an adjustable pressure switch on the manifold set to around 2psi to trigger a windshield washer pump to drive water into a small needle valve so you can adjust the water quantity going into the air cleaner. A better system would adjust quantity based on temperature of the housing. Like an Arduino with temp sensor PWM driving the washer motor.

Torlon is the space age replacement for the cloth/phenolic blades. Very expensive. A place down in Texas sells it. You will have to CNC cut new blades. Delrin and Teflon are not suitable.

If you have long drives to events, then I suggest removing the belt to the unit and wire the rotor so it does not free spin.
You can then run normally aspirated and save wear and tear on the unit. You can then put the belt back on at the event.

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Specialization is for insects.



Edited 4 time(s). Last edit at 2022-05-23 03:26 PM by 59undine.

David, I am attaching more detailed information regarding Torlon. The scans are from a trade journal Compressor Tech.
Drake Plastics stills sell the product. My Judson has Torlon vanes.

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Specialization is for insects.

Dean,
I don’t have a blower but have been reading this thread with interest. Thanks for posting so much detail.
One point confused me however. That is how can the engine work if you stop the blower from rotating as you suggest for a long journey? I would’t have thought there was a gas path from the carb past the blower vanes to the inlet manifold.

Interested Phil.