Noah :
Well, if it makes you feel any better, I have an original Judson sitting on
the dining room table, DCOE's hanging on the wall in the garage (both 40 and
45), and the way things are looking I'll probably just run the HS6s !
Other than being period correct, the Judson really is not very well designed
by modern standards, and has some problems. It uses phenolic vanes that
ride against an off-center cylinder as the pump mechanism, which means the
vanes have to be lubricated, and that they wear out. The lubrication oil
eventually finds it's way into the intake, which lowers octane considerably
(which is the last thing you want to have happen with a blower).
Apparently, the friction of the vanes on the housing both consumes
horsepower and produces a fair amount of heat, both of which are also bad.
Last, the intake manifold and 1 bbl downdraft carb that are used are quite
restrictive, which also doesn't seem like such a good idea. I don't know
how long the vanes last, but almost everyone I've heard from with a Judson
has either replaced the vanes, or is having trouble due to damaged vanes.
Replacing the vanes with Delrin is pretty popular, that's what I plan to do
with mine. Also, the drive mechanism is a bit strange, it uses a special
pulley on the water pump, that takes the original wide belt, plus two narrow
belts to drive the Judson. The pulley on the Judson is also a custom-cast
part, which makes it difficult to adjust boost levels. BTW increasing
engine displacement (like 87mm liners) will reduce boost, unless the pulley
sizes are changed. Oh, and many replacement water pumps do not have
removable pulleys. The original types are available, but you have to check.
One of the derned carb nuts on my original Judson is located in a really bad
place. No room for a socket, no room for a wrench. The reason it's still
on my dining room table is that I've not yet figured a way to get that nut
off. Current plan is to cut the side off of a socket that has wrench flats
on it ...
I'm not familiar with the Shorrock, and a little web surfing has turned up
conflicting information about which type of blower it has. One source says
they are a centrifugal blower design, another (which seems more
authoritative) says it's a vane pump, just like the Judson.
The centrifugal blowers have an entirely different set of problems. The
biggest one is that it has to turn at very high rpm, 3-5 times crank rpm, so
there is a step-up gear train involved. That gear train tends to be pretty
fragile, sudden changes in engine rpm (like winding it up and dropping the
clutch) can break it. They still sell centrifugal blowers today (Paxton,
common on Ford Mustangs, obvious because you can hear the gear train whine)
but they now have precision slip clutches in the gear train. I don't know
for sure, but I've heard the ones sold in the 60s did not have slip
clutches. Another problem with centrifugal blowers is that the boost
changes with rpm.
The 'vane pump' source says the Shorrock uses engine oil to lube the vanes.
That's nice in the sense that you don't have a separate jar to fill, but bad
because engine oil pressure is not constant, and with the jar you have the
option of using 2-cycle oil that doesn't hurt the octane as much as ordinary
motor oil.
http://mg-tabc.org/supercharger/Shorrock_ABC.pdf
IMO, unless you're worried about period correctness, the thing to do is just
get a bare Eaton (or whatever) and make up the parts to use it on a TR4.
One approach to the manifold might be to cut an original intake manifold
where the tubes meet the 'boxes' behind the carbs, and weld on a 4" square
aluminum tube. Then machine the other side of the tube to fit the blower,
and weld plates over the ends. A few years back, someone built a kit for
the TR6 this way, and was going to offer them for sale, but decided there
wasn't enough interest. One lister (Kai Radicke ?) has (or at least had)
one of those prototypes on his TR6, he seemed very pleased with it.
http://www.magnusonproducts.com/
Of course, as others have alluded to, you really need to drop the
compression ratio to be able to use any significant amount of boost on
modern pump gas. To do it right, you'll also want to use some ignition
retard, basically to carry the vacuum advance curve out into positive
manifold pressure.
While I'm obviously enthusiastic about such mods, I feel I should mention
that you're literally playing with fire. The road to supercharger success
seems littered with burnt pistons, broken rings and whatnot.
Did I mention there's a Team.Net list for Judson blowers ?
Randall
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