Since
1880 the Judson Family have been involved in some form of mechanical and
electrical engineering.
It's a story of enterprise and innovation, from farming machinery through
to electronics for the defence and automotive industries. Of course
stationed along the route was the Judson Supercharger, a product that was
a natural spin-off from a small interest in producing custom made racing
superchargers.
The supercharger manufacturing unit was part of Judson Bros. of
Collegeville PA,- who made farming machinery- and was absorbed into the
parent company, Judson Research and Manufacturing Company of
Conshohocken PA.
Production superchargers were developed in the late '40s starting with a sliding vane supercharger for
the Flathead Ford V8. A new supercharger for
the popular British MG TD sports car followed in the early '50s.
Production continued for a few years at
a modest rate but the breakthrough came when in 1956, a version was produced for
Wolfsburg's finest
and with the explosion in popularity of the Beetle in the U.S., production was moved to a
new factory to cope with the increased demand.
W. Haddon Judson was the
prime mover in the development of the company and in the technical
innovation of the supercharger aided by his brother Charles. New models were added steadily over the
years until the full range included superchargers for MG TD, TF and MGA, Renault Dauphine,
Triumph TR3 and 4, Mercedes 190SL, Volvo, Austin-Healey Sprite, the Corvair and of course
two versions for Volkswagens.
The two VW types were a natural
progression. The first was for the 30/36hp engine and the
second for the 34/40hp unit introduced in August 1960. For the Karmann Ghia the kit
included an aluminium air scoop for the deck lid but in all other respects the two Judsons
fitted across the range until the advent of the 1500 in 1967.
From the outset it didn't take long for the
enthusiasts to start looking for ways to make their Beetles keep up with the opposition.
A late
fifties advert
Conventional methods like increasing the compression ratio, twin carbs, modified cams and
other engine modifications always seemed to run into trouble with the 30/36hp's
notoriously whippy crankshaft when extending the rev range.
With the Judson
Supercharger, as a low pressure unit, extra
stresses are kept to a minimum. It should also be noted that crankshaft
failures are usually related to over revving...the Judson
produces it's extra power at stock engine speeds and NOT through extending
the rev range.
At this point let me dispel a popular misconception.
The Judson Supercharger is not a high performance add-on in
the modern sense. With the
limitations of the basic 36 & 40hp engine this is not the way to go if you want a
vintage VW that will keep up with modern GTIs.
It is however a period accessory that will
give a very useful boost in performance to lift your car out of that sandwich between the
two 30 tonners in the inside lane of the motorway . We've all been there at some time !
Left:
This advert from the late fifties shows W. Haddon Judson (front right) and
brother Charles A. Judson (next to him) demonstrating the Judson
Supercharger to potential customers
Lets Get
Technical (not very)
So how does the Judson produce the
extra power.
First of all it's important to
understand the breathing characteristics of the early flat 4 engine. Easy, it doesn't have
any! OK, an exaggeration but the designers at Wolfsburg deliberately created an engine
with restricted breathing, thus limiting the power output and in turn producing a low
stressed, long lasting unit.
The Judson is a sliding vane unit. It
compresses the mixture from the carburettor by means of a series of sliding vanes located
on an eccentric hub. As the hub rotates the vanes are thrown outwards and seal against the
wall of the supercharger, pressurising the mixture and pushing it into the intake
manifold. As a result the volume of air/fuel mixture supplied to the combustion chamber is
significantly increased, overcoming the restricted breathing of the normally aspirated
engine.
That's it in layman's terms, very
simple so the first question is; in improving the breathing characteristics do we
sacrifice reliability?
Large inlet
ports..............................
..................and small
outlets aid compression...........
..................the vanes fit loosely
in the rotor
The
answer to this is no. Supercharging produces its extra power through better
atomisation of the air/fuel mixture and a more complete filling of the
combustion chamber. All this extra energy is produced at the same rpm as the
normally aspirated engine meaning you don't have to rev the engine faster to
take advantage of the extra power produced.
Subsequently what you see here is that
supercharging increases the torque of an engine without spinning the engine
faster. It creates the power (on a vintage VW) where it's of most use, in
the mid rev range.
So the question of reliability is
that a Judson Supercharger doesn't overstress the stock flat four as it
doesn't produce the extra performance by extending the rev range. In most
cases, the Judson Supercharged engine is more efficient, cleaner running and certainly better lubricated.The
lubricator bottle is an integral part of the Judson set-up. It supplies an
intravenous drip of oil to lubricate the phenol impregnated linen vanes of
the supercharger and is burnt with the fuel mixture in the combustion
chambers. This oil also acts as an upper cylinder lubricant.
Performance
Performance figures for Judson
powered VWs come from just a couple of reliable sources that I know of but if you have any
others then I'd be pleased to reproduce them here.
The first is a road test carried out
by "Road & Track" magazine and published in September 1957 and the second
from Aussie magazine "Wheels"
published in October 1960.
Most Judson owners have their own set
of performance figures but I'd rely on the more scientific magazine test, than on the
observations of a notoriously optimistic VW speedo. The most often quoted comparison of
the supercharged VW is that it is equal to a 1600 single port engine.
One has to note that adding a Judson
to an under performing stock engine will only add to the problem. The stock engine, (Judson
insist) must be in good condition, well run-in and properly tuned. Adding the Judson to
anything but a well tuned VW will emphasize shortcomings in electrics,
carburation, and
cooling.
others then I'd be pleased to reproduce them here.