Super Coupe Club of America > SC Literature > Super Ford's Blower Build
by Isaac Martin
photography by the author
We find more efficiency and an affordable alternative to
costly replacement for the Super Coupe blower
Blower disassembly begins by draining the lubricant in the reservoir through the front
access plug. It's a special lubricating oil developed by Eaton and can be reused. Now unscrew the retaining bolts.
(Bottom left) To break the seal between the snout and the body, tap the snout gently with
a soft-faced mallet, until the two halves break free.
(Bottom right) Using a special jig, the rotor pack is pushed out from the rear of the blower
body. It's replaced in the rebuilding process, in fact, ultimately the only components reused
by Magnuson are the blower case and nose.
As this blower-packed issues illustrates, it's been raining superchargers around here. Along with our BBK/Eaton story on
page 28, we spent a day at Magnuson Products, authorized Eaton supercharger representative
for sales, service and aftermarket applications.
Jerry Magnuson has three decades of blower experience, including building his own line of roots superchargers that was
used on everything from nitro drag bikes to big-block trucks. You may remember his Magnacharger line, especially the
V8 units. They were unique in that he cast two blower housings at an angle to get a large enough blower. He
sold his blower line to B&M awhile back, but now has the Eaton franchise to service. This is a good thing for the
Thunderbird SC owners who are looking for an upgrade. As Jerry says, having the Eaton account is like "being the
Maytag repair man," as the robust OEM superchargers rarely break, and don't loosen up until they've given well
over 100,000 miles of service, so finding someone familiar with the blowers is practically impossible.
Removing the drive pulley is simplified by using this special fixture
to hold the blower in place. This is important, because otherwise
you could damage the housing nose.
With the nose off, a small ring retainer
using small needle-nose pliers. This
retaining disk. Pressing the driveshaft
out of the
blower case nose is next.
After pressing them free, the driveshaft and
pin drive are removed from the other side.
All these items are replaced with new parts.
Like all good hot rodders, Jerry is offering more than
simple Eaton rebuilding. He has a few tricks he can play on the M90 Eaton,
including cleaning up the case for improved airflow. Also, when it comes
time to rebuild that Super Coupe engine, Jerry can upgrade the earlier
M90 blowers (the '89-'93 units) to the later, better breathing style.
While supercharging is rarely inexpensive, Jerry can also
help in a major way with the cost. A '90 SC blower assembly from Ford,
part number F) SZ-6F066-A, is a mere $2560 for the entire unit. This, of
course, is the only way Ford services the blower. Not that Eaton's are
likely to need rebuilding, but as time passes, more SC's will accumulate
mileage and could benefit from freshening. At $2600 out the door for the
blower plus whatever goes into the engine, such freshening probably translates
into buying a different vehicle and casting the old SC into outer darkness.
Magnuson's prices are far saner than Ford's. A rebuilt
assembly has a suggested $995 list, plus a $325 core credit. Flow modifications
are optional for an additional $200, and they are performed only on the
latest case ('94-'95) with the rectangular opening. A new Ford unit is
$1625 from Magnuson. Basically, the modifications smooth air flow around
corners to help blower efficiency and power at high rpm. Thus Jerry can
make sprucing up a Super Coupe economically feasible, plus add a bit more
power along the way. We've detailed the M90 overhaul and modifications
in the photos.
In case you are wondering about the upgraded Super Coupe
blower Ford SVO was offering, it is no more. It too was an Eaton, boasting
Teflon-coated rotors and a slightly smaller blower pulley. Priced in the
stratosphere alongside its regular production counterpart, the SVO blower
was never a hot seller and was quietly dropped. Thus Jerry is the only
game in town we've heard of for tweaked SC blowers.
Besides covering the Eaton build, we also picked Jerry's
brain on roots blowers in general. With the 5.0 market awash in Centrifugal
blowers, the roots design has fallen out of many enthusiast's minds. Thought
old, noisy and inefficient, the roots actually has plenty of life in it.
Eaton's betting on it--$50 million they've spent on building a line of
OEM-level roots blowers to meet car maker's performance, durability, quiet
operation and compact engine packaging demands. A large OEM supplier, Eaton
has determined the market for the relatively inexpensive, torque-enhancing
forced induction will grow tremendously, and has invested accordingly.
These are early and late blower drive isolators. Below
is the early
('89-90) style solid coupling, using only a phenolic
for the pin drive. On top is the later ('91-on) torsional
further isolate rotors from the blower drive vibrations,
engine speed changes, and to minimize noise. For maximum
performance, you want to retain the solid coupling, as
swings stress the isolator spring.
Magnuson's rebuild kit includes all
driveshaft, torsional spring isolator
and pin drive.
If you have an early style blower rebuilt,
is automatically replaced with the quieter
Up front, a retaining disk and shaft support
bearing are removed from the case.
The rear rotor shaft support bearings are pressed out
of the case and replaced by a new set.
Needle bearings are used in this location, and they are
lubricated by a special grease developed by Eaton.
Origionally, Eaton rotors ('89-93, left) were just bare
Replacement rotors ('94-'95, right) are now epoxy-coated.
The epoxy-coated rotors offer high lubricity and less
Plain aluminum rotors needed larger clearances, whereas
coated rotors reduced clearance and yield improved pumping
Mechanically, the compact Eaton is a roots-style, positive-displacement
blower with two tri-lobed rotors twisted in a 60 degree helix to reduce
noise and improve volumetric efficiency. Eaton's design has patented features,
like slots in the top of the housing to reduce noise. Helix rotors and
special inlet and outlet port geometry combine to produce a smooth discharge
flow which further reduces noise. The Eaton also has a bypass valve, which
recirculates supercharger airflow under non-boost conditions; considering
the engine is under boost only 5 to 10 percent of the time, the engine
operates largely under vacuum. As for the long haul, the Eaton package
passes 500-hour durability tests an OE 100,000-mile vehicle requirements.
As Jerry explains, the involute rotors allow more compressor
displacement, and improved sealing management, with very little air carry
back to the inlet tract. He adds the Eaton has high adiabatic efficiency
for a roots blower. Adiabatic is a comparison of air temperature rise between
inlet and outlet air from a blower and the power used to create the boost.
As air is compressed, heat is generated, reducing engine performance. A
25-degree inlet air temperature increase costs approximately 10 horsepower.
So, the smaller the temperature gain, the more power you get. An M90 with
a 2.5:1 drive ratio, has a 65-percent adiabatic efficiency between 1600
and 2400 engine rpm. In other words the higher the adiabatic percentage,
the better. Of course, you can't forget intercooling, used on the T-bird
SC, which further reduces boost temperature.
Blowers can also be considered in terms of volumetric
efficiency, and like engine VE, this is a comparison of actual inlet flow
compared to the blower's theoretical displacement. According to Eaton,
the M90 with a 2.5:1 drive ratio has a volumetric efficiency of 83 percent
for 10 lbs of boost at over 4000 engine rpm.
The supercharger cases also differ. On the left is the
early case, identified by the oblong opening, and on the right is the later
rectangular opening. The oblong opening measures 4 x 1.437-inch and yields
a 4.319 square inches of opening. A slotted rectangular case measures 4.250
x 1.500-inch for 6.375 square inches. The slots on the top of the case
(ARROWS) are for noise control. Also remember that as the rotors turn,
air is forced up the sides of the case and not squeezed between the rotors.
Jerry also offered some additional performance observations
to dispel old roots falsehoods. Spinning a blower harder may get more boost,
but that doesn't automatically mean more power. In the case of the Eaton,
it's not a high pressure device. As he explains, it's pretty good at 11
or 12 lbs of boost, but it's dynamic a 8 lbs. The basic principle is high
volume, low pressure. When you start moving out of that area, you're defeating
the purpose of a roots blower.
Magnuson's optional flow modifications
begin with beveling the case's air intake edge. The area is coated with
machinist's dye and then the width of the bevel is scribed with a set of
Jerry also talked about overall system efficiency. In
other words, bolting a blower on makes power, but if the throttle body
is restrictive, or the cam is mismatched, you won't get as much power as
you could. In his opinion, people make the presumption that if the supercharger
is efficient, the engine is efficient. Yet air intake to exhaust system
efficiency is by far the controlling performance medium. Improve the engine's
induction and exhaust, and you'll get more power per lb of boost. In the
case of the Thunderbird SC (and Cougar XR-7) installing a larger diameter
throttle body and opening up the exhaust would be good places to start.
Together, you probably would see lower boost, yet increase performance.
That's because some of the boost showing on the stock engine is really
back pressure holding the inlet air up. Free up the exhaust and the restriction
goes down. More air will flow through the engine at a reduced pressure.
Thus boost goes down while power goes up.
Material is first removed with a die grinder,
then it's polished with a cartridge roll.
The radius is then checked with a template for consistency.
Before grinding, tape is placed to cover the rear rotor
shaft needle bearings, since any metal fillings would
In the case rear, it's machined for
rotor clearance and leaves
a squared-off end (left ARROW). Magnuson
bevels it off to produce
a smooth exit for the air (right). What
do these modifications deliver?
According to Jerry, power increases
are noticeable at high blower speeds,
where airflow picks up. The mods also
deliver a bit more adiabatic efficiency.
This is a 3.8 supercharged intake manifold which the
blower sits on.
Pressurized air enters the rear opening. The manifold
a giant plenum where the air enters the head ports. If
you add a later
rectangular port blower, you have to install a matching
This is the rear of a 63mm SC throttle body.
If it were larger in diameter, you could pick up some power, just like a larger diameter throttle
body helps supercharged 5.0
The trouble is, no one makes a larger diameter throttle body for the SC engine.
Here's a completed blower, ready for a long performance life.
The M90 is compact, measuring 7.55 inches wide, 5.40 inches tall,
and overall length from the case rear to mid-pulley is 16.35 inches.
That's the theory. For Eaton blower nuts and bolts, follow us through the rebuilding process. Along the way we'll show
how to identify early and late blowers and how Magnuson Products improves high-rpm performance.
"Basic Bolt-Ons and More"
BBK/Eaton supercharger--Jan '95 SF, page 24
3172 Bunsen Ave
Ventura, CA 93003