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.

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 plastic isolator

for the pin drive. On top is the later ('91-on) torsional isolator to

further isolate rotors from the blower drive vibrations, during

engine speed changes, and to minimize noise. For maximum

performance, you want to retain the solid coupling, as high-rpm

swings stress the isolator spring.

Magnuson's rebuild kit includes all new bearings,

driveshaft, torsional spring isolator and pin drive.

If you have an early style blower rebuilt, the isolator

is automatically replaced with the quieter torsional style.

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.

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 calipers.

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.

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 be unwelcome.

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 interior forms

a giant plenum where the air enters the head ports. If you add a later

rectangular port blower, you have to install a matching intake.