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MG MGA - Judson Input Needed

Well I bought a Judson. Will these work on an 1800cc engine or are they too small in cfm capacity to produce a significant amount of boost? Will the oiler that Moss sells work instead of the Marvel/Judson oiler normally supplied? The one I bought did not come with an oiler.
Dominic are you out there?
James Johanski

Jim:

Until Dominic signs on...The Moss Ampco oil unit charged with Marvel Mystery Oil should work just fine with the Judson. In good shape, the Judson will develop 5 - 6 psi boost and will work as well with an 1800 as with a 1500 or 1600 displacement engine. 200 or even 300 cc is not enough change in total displacement to show up in blower performance. Remember that the total displacement is 4X the displacement/cylinder. The valve size and cam timing has a much bigger impact.

Steve
Steve Brandt

Instructions and lots more is available here:

http://clancy.ch/Judson.html

A separate Amco oiler is fine - you can also buy one from George Folchi, who is a guy that you definietly will need to contact.

You can contact me directly on dominicATclancyDOTch
dominic clancy

Steve and Dominic,

Thank you for your answers. I believe the ultimate boost is a function of booth the speed that the supercharger runs and the displacement of the supercharger vs engine displacement. So unless the supercharger is driven at higher speeds than in the MGA configuration the ultimate boost should be less on an 1800 engine as opposed to a 1500 engine--Comments?
James Johanski

James,

See the SuperCharging section of this message board for a lot of good information. I've had a Judson for a couple of years now. Dominic was a big help in getting it set up correctly, particularly with his recommendation of George Folchi. George did a great job of putting all the right pieces together for my setup, along with a nice refurbishing job on the blower.

On installation, the toughest parts for me were bolting the heavy blower, and dealing with clearances around the radiator and blower pulleys. I recommend a gullible friend or engine lift help out on the blower installation.

-Chuck
Chuck Mosher

Jim:

Of course you are right about the extra displacement affecting boost pressure. Pressure and volume are inversely proportional. My point was that although there is a 20% difference in displacement between a 1500 cc MGA engine and an 1800 cc MGB engine, the difference in performance depends on more than the volume displacement of the Judson. The B has bigger valves (more gas in and out) and breathes better tha the 15 head. On the other side, because of its vane design, the Judson's blower efficiency is not the best. You can probably increase the efficiency of the Judson by rebuilding it and making sure the vanes are not worn and the bore is smooth to boost pressure. You can also have a larger crank drive pulley machined (within space constraints). Decreasing the diameter of the Judson drive pully will also increase boost, but you will reach a limit at which the vane blower will not be able to pump against the inlet back pressure. Five - six pounds of boost seems to be about all that the Judson can put out before the design of the unit limits the pressure. There is no blow off valve with the Judson, because none is needed.

Steve
Steve Brandt

One thing you might carefully inspect for stress cracks, Jim, is the support arm for the idler pulley. Judson's design for the MGA is only slightly different from that for the Volvo P1800, and at least for the latter blowers this part was an achilles heel. It broke with some regularity, and many of us who ran a Judson kept a spare arm in the trunk. It helps not to overtighten the arm after tensioning, but then the belts shorten upon heating at high rpm and throw the idler out of adjustment. It's also very important to have no excess play in the idler pulley bearings, as too much vibration on its shaft hastens fracture of the arm. It takes a bit of diddling to get it right.

Ken
Ken Korey

This thread was discussed between 12/01/2008 and 25/01/2008

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