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MG MGA - Another Judson

It seems these Judson superchargers are becomming commonplace! Another one has appeared on eBay. The last one ended up going for quite a (relatively) low price, I seem to recall.
Oh, and Steve, a nice Shelley jack!
Neil McGurk


Seen it. And for once it's correct version for the MGA.

Steve Gyles

There are actually two available on ebay at the moment - something I have never seen before.

This one is missing some important bits:

1. The manifold between the blower and the head, this will be hard to find unless George Folchi has a spare one
2. The Crank pulley is available from George (or I have a surplus one)
3. The oiler valve cover is missing, though an external oiler will be fine.

It's worth reminding potential buyers that if the rotor is worn, it won't perform well, and you can't se that from outside.

Don't pay anything for copies of instructions for either the blower or the carb, both are available from me or online. (someone paid 20US for a set of these on ebay last week!

The other one: Much better looking and complete 160176607191, but much more expensive

And as for the $630 220164591457 or even $700 gauge... 300170780753 - I can provide instructions on how to make your own for less than $100, and provide a ready-to-print picture for the dial.

Full service at your fingertips!
dominic clancy

Please e-mail me instructions for the Judson. I have one, but it was copied so many times it is not clear. I would e-mail you, but it does not show.

How does the performance of a Judson supercharger relate to the performance of a cross-flow cylinder head?

Darian Henderson

Dominic, -- You say "instructions for either the blower or the carb, both are available from me or online". I don't need copies for myself, but I would like to know where on line so I can make a link to it from my web site.
Barney Gaylord

Yea for Barney,
Get them up and make it easy for us to make copies

I'll scan them in again with a new programme that makes the pictures better without them being huge, then send them to Barney - it's really time I got my own site up and running, especially as all I have to do is the ftp...

Darian asked about how easy it would be to fabricate the mising manifold. I suspect a bit tricky, as this is dimensionally very important. It supports the whole weight of the SC, and aligns the pulley to the belts. It has therefore to be accurately parallel at the face between the manifold and head and between manifold and blower housing. It also needs to be strong, as these things are heavy. An original inlet manifold will give a good template for the head side, but would be nowhere near strong enough to be used as the basis. The SC side is fairly simple with just a large flat oval port to match the SC. But the fore-aft positioning is critical for the correct belt alignment, and there is VERY little space for any messing around - best done with an engine out of the car.

As to how a Judson car compares to a crossflow head - no idea, as I have never driven a Xflow engined car. But feel free to come and try the Judson out.
dominic clancy

Any blower, Judson, Moss, Hans Pedersen, as well as turbos work by force feeding more air and fuel into the combusion chambers, resulting in bigger controlled burns (explosions, if you will). The bigger bang translates to more horsepower and torque for a given displacement. The downside is that the higher the blower spins, the more mixture that is forced in and the more combusion by-products have to be swept out of the combusion chambers. Generally, that limits the useful top end range of the blower along with the rotating mass at very high rpms. So, as a general statement, for non-purpose built engines, blowers are most effective in the low to mid rpm ranges.

Cross flow heads are designed to sweep gases through the combusion chamber more efficiently than same side exhaust/intake configurations - effectively increasing the pumping efficiency of the engine. Cross flow heads benefits increase with increasing rpm as the duration times of the intake and exhaust cycles decrease.

There is some synergy that can be had by combining the blower with a cross flow head to move more mixture and exhaust through the engine. Unfortunately, for the MGA/MGB, this would involve building a custom blower manifold for the cross flow head. Some participants on the supercharging BBS have discussed this configuration from time to time, but I am not aware of anyone who has actually built such an engine.

Steve Brandt

For the XFlow head on a A you would have to use a different Judson blower casing that is designed for mounting on the other side of the engine. There are lots of these, but they all combine the inlet and outlet manifold into a single casting, which would make fabrication even more tricky. Another complication is that these are all just as rare as the MGA Judson, judging by how many come up on ebay. It seems that many of the casings and rotos could well be common to many models.

Candidates would be the TR3/4, Corvair, Volvo blowers. In the last year I have seen a few TR3 units, one corvair unit and no Volvo units available.

Would be interesting to drive that combination if it can be made to fit without fouling the distributor (which I doubt), and of course the dynamo would also have to be re-sited too.

Definitely a project for someone who is handy with casting and welding!
dominic clancy

Well, that explains a few things. My A has a cross-flow head and a 3/4 racing cam. It's OK at 2,000 RPM, but it is MUCH more fun to drive in the 4-5000 RPM range...

Darian Henderson

OK, I finally loaded my site up - just a small one with lots of pictures and a "parts for sale" section, but it's got lots of stuff on Judsons for the MGA. I will do more when time permits.

Have a look:
dominic clancy

Nice job Dominic, you have mail!
Neil McGurk

This thread was discussed between 11/11/2007 and 13/11/2007

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.