I was looking up things on our superchargers and I found out some interesting info. We'll start with my fav, the M62A 3rd generation:

The Eaton Model 62 supercharger was engineered for 2.0L to 4.0L passenger cars and light truck engines. It was designed as a compact, flexible supercharger for increased power without adversely affecting fuel economy. The M62 has proven to be suitable for other engine sizes depending on overall system requirements.

Most installations see a realistic 40% plus increase in power output.
Eaton Superchargers will work effectively in any orientation (Flat, upside down, on edge).
Different length drives are available, giving the custom installer flexibility in the placement of the supercharger.
The M62 is available for counter rotating engines (2 Piece Drive).
A Bypass Valve is included with every supercharger, two different Bypass Valves are available, one that mounts directly on the intake port, and one for remote mount.

At 14000rpm and 5psi of boost it flows 460cfm. But at 10psi it flows 440cfm. Picture what the people running 13-16psi are getting in terms of actual flow.
The temperature is also night and day between 5 and 10psi. At 5psi (14000 rpm) the delta temp is 115deg F. Move that up to 10psi and we get 180deg F.
Now lets look at the parasitic losses associated with this supercharger. At 10psi and 14000rpm we lose 36hp trying to spin it. Wow I hope the gains are more than 40hp! At 5psi we only lose 24hp. They really should come up with better lubricants for these things!

So onto the M90:

The Eaton Model 90 supercharger was engineered for 3.0L to 5.7L passenger cars and light truck engines. It was designed as a compact, flexible supercharger for increased power without adversely affecting fuel economy. The M90 has proven to be suitable for other engine sizes depending on overall system requirements.
Most installations see a realistic 40% plus increase in power output.
Eaton Superchargers will work effectively in any orientation (Flat, upside down, on edge).
Different length drives are available, giving the custom installer flexibility in the placement of the supercharger.
The M90 is available for counter rotating engines (2 Piece Drive).
A Bypass Valve is included with every supercharger, two different Bypass Valves are available, one that mounts directly on the intake port, and one for remote mount.

Now looking at the M90'* flow rate we see 540cfm at 5psi and 520cfm at 10psi. It still gets the same level of loss as boost goes up as did the M62. The temp at 5psi is 120deg F and 190deg F at 10psi. Interesting it runs hotter huh? So all that flow creats more friction and hence more heat, our enemy. I wonder how much power it takes to spin this joker. Well at 5psi we have a parasitic loss of about 29hp but move that up to 10psi and we lose an astounding 44hp! And this is supposed to be the better model? Yeah yeah I know, 100cfm is a big difference. But it comes at a cost of heat and power required to spin it which pull your gains down. Just thought I'd drop some interesting info on you

thanks for the interesting info Dr Jay. I went with the 2.4 pulley which was one size smaller then the recommended minumum 2.5 and i am running at about 14 PSI at WOT. i can attest to the fact that it has more power at 3/4 throttle then WOT. WHen its to the floor and my boost gauge goes over +10, it boggs down more then anything else.

do you think P&Ping the intake and exhaust would help the flow better or is it an inherent shortcoming of the SC itself due to heat?

Porting and polishing the heads will give you more flow and more power. Plus it will bring down the boost and you can then go to a smaller pulley (maybe, though I doubt it.)

hey hector! The heads huh? So dont worry about manifolds yet then? If i P&P the heads, do internals need to be replaced because of the size difference?

Unfortunately i am stuck with the 2.4. i dont want to get another 2.5 at the price they run.

L8rs

Those HP losses ALMOST make me feel better about NOT having the little "i" (Hey Im looking for ANY exuse...) ......

Ya right. ....

I have always said that I liked turbochargers better...the 44hp loss at 10psi is probably why. So theoretically a turbo putting out the same boost and CFM as the M90 would be making ~44hp more on the same engine if I am understanding this correctly?

So the smaller pulley is a ...someone else say it.

Ty

If you get water injection in that should help lower the intake temperature and give you more power. I wouldn't say the smaller pully is a waste your getting your power sooner in the band.

A smaller pulley isn't anything but a way to make more power (assuming you can stay away from knock). Those numbers are misleading. It takes the engine 44hp to spin the blower at 10psi according to that, but the power that the blower makes way more than makes up for the 44hp loss, if it didn't superchargers wouldn't do anything.

For instance we have a 2.7" pulley on the GTP on the street, that makes 14.3psi, so that takes lets say 50hp to turn (I have no clue what the number is so I am giving a rough example), but the extra power made from the boost may be 150hp, so really the blower just added 100hp to the engine, get it? But if you had a turbo that flowed the same CFM and made the same boost it wouldn't take any of that power to run it so it would add 150hp to the engine instead of the 100hp the blower adds, you just wouldn't have as much low-end torque as you do with a blower because the turbo has to spool. Understand?

But turbo'* do make more backpressure if i remember correctly, and depending on your exhaust setup, and how well it'* tuned to your engines output of exhaust that could be good or bad.