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February 28, 2003


Hi, Nigel...
This Judson is the American counterpart
to the British Shorrocks back in the days
when 100+RON leaded gasolines were
readily available at the corner pump at
reasonable prices.
Neither of these "low pressure" supercharger applications were designed
for anything but "temporary" boost operation. They are "torque" rather
than
"HP" applications...."stoplight drags" rather than "track", "temporary"
operation
rather than "constant" operation.
Both were designed as bolt on intallations
involving no more than a change to colder
spark plugs, the idea being to temporarily
superimpose a 6 psi boost curve upon the
stock ignition advance curve for a temporary increase in torque
(acceleration). Note the constant use of
the word "temporary"! :)
Today's gasolines won't support the applications except by lowering the
static
compression ratio to 8.0-1 or below. Cooling mods will also be required
as in
alum.head/rad and cold air induction, louvers and limited ignition
advance as
well a modified exhaust system to get the
heat out more quickly.
Vane type blowers are the "compression
heat" producers of the supercharged set,
by design. Lobe and centrfugal types run
cooler per pound of boost produced.
While the Shorrocks runs clearanced vanes, the Judson runs
"interference"
vanes and thus is more of a heat producer
than the Shorrocks, by way of blade friction.
Heat is the biggest product of boost. This
is especially so with these vane type blowers, the Judson being the
worst offender in this respect with the understanding that 6psi boost
will increase the dynamic compression ratio
4-5 full points...that's a lot!
The Judson was originally designed and
built by the Judson Brothers of Pennsylvania back in the late 1950's
and
early 60's for the original 8.3-1 948cc
engine powering the Bugeye.
The set-up requires (and normally comes
with) a Marvel Mystery Oil "Oiler" which
consists of a tank and graduated settable
valve to supply a drop of 10wt oil to the
blower every 4 seconds at idle rpm, via
a tube running between oil and blower
intake manifold. The oil tank needs periodic filling as the blower will
use about a US quart every 700-800 miles.
With stock pulley it will produce:
a 6psi boost curve to a 948cc engine
a 5psi " " " 1098cc engine
a 4psi " " " 1275cc engine
The designed 6psi boost curve gave the
"948" about a 40% increase in low and
mid-range "torque" in accordance with
the stock cam profile as intended as a street application. This really
worked,
BTW. It cut the 948 BE's 0-60 time down
to about 12 seconds from 20!!
Unfortunately:
You will get substantially less than this
with the larger capacity engines, to the
extent the application makes no sense
for the "1275" as you will get virtually
no boost below 3,000rpm (just induction
heat caused by compression heating of
the mixture along with blade/bore friction) and little boost thereafter
until you get to around 5,000rpm. Of course your redline
is barely 6.5k. Doesn't make much sense,
does it?
While you can fabricate smaller blower
pulleys to run the Judson at higher rpms
than the 6,100 it turned at 6,000 engine
rpm on the 948 engine, it's interference
vane construction does lend itself to
"overdriving" due to centrifugal forces
which load the interference vane/bore
design with friction (heat) as you drive
the application out of it's VE (volumetric
efficiency) envelope. This doesn't do anything for blade/bore wear and
tear, either. In other words you really
need a larger capacity blower.
You might get away with this on a 1098
but you won't with a 1275 (BTDT). Modern
Delrin vanes would help but, these begin
to melt just short of 200F and the Judson
blower case already runs at 165F on a
75 degree day....out of boost, no less!!
So this won't work because the vanes
start melting and deforming.
The "interference vane" set-up is a real
heat producer by design, as you can see!
Imagine the amount of heat this application would produce "overdriven"
to obtain the originally intended 6psi boost
curve on the larger capacity motors!! Whoa, whoa....!! You'd be turning
at
least 7,500rpm, maybe more!
Now you say..."Well, hell, I'll just retard
the timing a bit and go to a lot colder spark plug"....ok....say
"goodbye" to fuel
economy and "off boost" performance
and "hello" to plug fouling during "off boost" operation. Don't forget,
you're
introducing oil (for blower lubrication) into
the combustion process. The application
becomes "non-streetable".
Speaking of which...you know that oil
dilutes octanes, right. Now you might get
away with diliuting 100+RON leaded fuels
and still have the octanes to handle the
heat of supercharged operation, but.....
you haven't got those octanes around
anymore....unless you wish to purchase
racing gas at US4.50+ per US gallon (this
WILL work BTW..BTDT).
The only way you can get a Judson to
work on today's unleaded pump premiums is by a alcohol/water (60/40)
"delivery" (as opposed to "injection")
system, bearing in mind the interference
vane construction produces substantial
heat along with the "compression heat"
vane-type blowers are noted for.
You'll need a "little" for off boost operation
and a "little more" when you put your foot
in it.
And of course, today we have modern
synthetic oils who's film strength and heat
handling characterisics are way better
than those of even the best mineral oils,
or even Marvel Mystery Oil which was
used in the "oilers" instead of 10wt mineral oils of the day, back when
(and
even today!).
Now, low pressure supercharging does
work. I have overdriven a Judson for a
6psi boost curve on a stock 1275 engine
running 100% 112RON leaded CAM2
racing fuel, utilizing the stock ignition
advance curve (Cooper "S" #40819 dizzy)
and man...it works. Car goes like hell but,
the blower case starts leaking and the belt
starts slipping on the smaller blower pulley used to overdrive the
blower, almost immediately.
But man, the car accelerated like a
raped ape!! This stuff really does work.
I would go with a "High-Flow" (MiniManica) kit, though. A lot more
expensive but....it's a complete and well
thought out kit. And, unlike the Judson,
it is designed with today's octanes in mind
without all the supplementary oiling apparatus, etc.
Cap'n. Bob (Ret'd)
'60 Frog

PilotRob@... 19650

Posted on February 28, 2003 08:20 AM
Posted to category(s) Carburetor | Cooling System | Cylinder Head | Electrical System | Engine (external) | Engine (internal) | Exhaust System | Forced Induction | Fuel System | Gauges | Ignition System | Intake System | Interior | International | Lubrication System | Miscellaneous | Racing | Restoration | Technical Info | Transmission | Tuning | US States

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