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MG MGA - Judson setup

In another thread, the subject of setup for a Judson supercharger was raised. Since it was getting a bit off topic, I started this thread.

Dominc, my carb has #62 jet. I don't know if that's right but suspect it's in the vicinity. As I was getting some detonation, I'm suspicious that it might be erring on the lean side. I was running the car on 91 octane fuel, which if I understand the difference in octane ratings between Europe and North America, would be around 95-96 on your scale.

I'm confident that the problem wasn't caused by too much ignition advance. My distributor was recurved for supercharger use by Jeff S at Advanced Distributors. He suggested starting at 18-20 degrees BTDC (dynamic). That just didn't work for me and I had it dialed all the way back to about 11 degree BTDC.

I am VERY interested to find out how other Judson users have their systems set up.
Andy Bounsall

My Holley came with a 52, have changed also for a 62.

I've just discovered a crack in the Judson casing as I was preparing to refit it now the engine is run in, so it's off for a repair. A new Judson owner is coming to see me tomorrow, so I'll try and see what he has in his too. I now know of four units here in Switzerland, so the rarity value here is diminishing fast!

Just fitted the new crank pulleys from George, using the harmonic balancer from a B, very nice finish too. If anyone is interested in the custom three-vee pulley that I had made (allows the use of the original dog nut for the crank) please do get in touch

dominic clancy


My Judson is in the shop too to have a crack repaired. The bolt hole which holds the unit to the intake manifold the center one has cracks and metal fatague. There is also is a crack inside just under the bolt hole. He has to cut out a section and reweld to fix both the cracked bolt hole and the crack inside. I need this unit to go to N. California for a Namgar Regional Show at the end of the month. Hope all is well with you.

Jeff B

Hi Jeff. Must be old age, as these Judson things seem to all be "cracking up"..Dave Godwin has had a similar problem with ONE of his.
Gary Lock


That is exactly where mine has issues too. It's only cracked at the bolt hole, but shows some discolouration in the barrel underneath that bolt, but as far as we can detect no cracking. It would seem to suggest that the centre bolt should be tightened a little less than the outer ones.
dominic clancy

I have made up a distance tube for the centre bolt. I suggest that over-tightening of the centre bolt is not necessary, and it should on be nipped up. Unlike all the other bolts on the unit, this one has a void between the surfaces, all others mate with a flat metal to metal contact.
dominic clancy

Cheers again Gary,
I hope you had a great time after we met with Dominic and enjoyed our day sight seeing and wine and beer. I have two Judsons and it is the second one that I am working to repair. The Judson is also broken on my car that happened on my way to Reno for the Namgar GT. The car runs without the Judson working as it froze up on me and I had to remove the drive belt.

Dominic, what did you use to make the spacer for that bolt and what length did you make it. I want to prevent it from happening again.

Just got home from our car club show and I took 3rd place.


This thread was discussed between 13/09/2011 and 19/09/2011

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