Originally Posted by Edubs

There are many different opinions and views regarding how to modify the M-Series, roots type, superchargers made by Eaton. In a recent discussion on another forum, a lot of information was uncovered, along with a solid contact within the Eaton Corporation itself. This thread will outline the findings and what is recommended by the manufacturer itself.

Both the M62 and M90 (most common on this site) are at their peak efficiency levels from the factory. Although running a smaller pulley is the easiest way to generate more power with these applications, it is also the easiest way to push the blower out of its efficiency range and produce gobs of heat. Heat, as you know, is the enemy of all F/I applications. Roots type superchargers, although extremely reliable, are the least efficient due to their drag on the engine by belt as well as their tendency to generate good amounts of heat in regards to the IAT (Intake Air Temperature). Eaton addressed some of these issues when they created their new line of TVS blowers; however, this thread is only concerned with the M-series blowers.

From Eaton.com:

"Eaton manufactures highly engineered, roots-type positive displacement superchargers. The Eaton supercharger increases torque across the entire operating range without compromising drivability or emissions. This allows vehicle manufacturers the option of using smaller, more economical 4- and 6-cylinder engines, without perceived loss in power train performance. Additionally, the supercharger incorporates a bypass system to reduce air handling losses when boost is not required, resulting in better fuel economy. Typical applications are on engines with displacements of 1.8L to 5.3L.

All aftermarket and service (rebuilds) are handled in the United States by Magnuson Products, (www.magnusonproducts.com) and in the Oceania-Asia-Pacific region by Harrop Engineering. (www.harrop.com)

The Eaton Supercharger - One Simple, Powerful Solution.

Eaton’s Air Management Systems Division designs, manufactures and markets modified Roots-type positive displacement pumps, also known as “superchargers,” for the original equipment and aftermarket industries."

When it comes to modification of these superchargers, the common areas of modification are:

Porting of the inlet portion of the housing
Porting of the internal housing
Porting of the outlet plate of the housing
Porting or Plugging of the "holes" on the outlet plate
Running a smaller pulley
Heat reduction, supporting modifications

The basic idea here is to increase CFM without raising IAT's. As most people on this site drive vehicles with the LSJ engine, M62 application, I will focus on that. These basic principles can be carried over to any other application using an M-Series blower. It should be noted, that the M-series superchargers are effectively air pumps. They do not internally compress the air themselves, but push it into the lower intake manifold. It is in the lower intake manifold that positive pressure emerges. Most folks think Eaton's roots-type units are actually squeezing the air like a screw unit. This is not the truth. No air passes between the rotors, the air is guided by the rotors along the sides of the housing; hence, no internal compression of air.

Porting the M-Series Supercharger:

It is not a good idea to remove too much material from any portion of the blower. Extreme porting of the blower will disrupt the air and will reduce efficiency greatly. A light porting of the inlet housing will help increase intake CFM of the pump. Typically, if a TB (throttle-body) upgrade is available, it helps to match the TB port size to the inlet port for a smooth intake of air with minimal disruption. Smoothing this opening up and enlarging it slightly will help introduce more air into the rotor housing which can then be "pushed" into the lower intake manifold. The inside of the housing can also be lightly ported to increase internal surface area. It is important to note, that internal porting of the rotor housing should be very minimal. Basically, remove any and all casting flashes and ensure complete symmetry while removing as little material as possible. Removing too much material will interfere with air flow and the functionality of the rotors. The output plate at the base of the M62 housing is what can be modified the most. This plate has one large triangular and two small oval passages in it. Right now, we'll focus on the large triangle. This is the passage that air is pushed through by the rotors to create a positive pressure in the lower intake manifold. This passage can be opened up slightly and smoothed out for best flow. Opening it up too much will also disrupt airflow. This is the most porting that should be performed on an Eaton M-Series blower to maintain efficiency.