The M90'* flow rate is 540cfm at 5psi and 520cfm at 10psi.
Is this correct :?: Less flow at higher pressure I suppose it is, based on the higher heat since warm air is less dense.
The temp at 5psi is 120deg F and 190deg F at 10psi.
So all that flow creates more friction and hence more heat, our enemy.
At 5psi it has a parasitic loss of about 29hp but move that up to 10psi and we lose an astounding 44hp!

.....is it better to feather the throttle and keep the boost around 5 psi :?:

Nahhhhhh......floor the sucker and smoke those meats.

IF that were the case then wouldnt it help to have some kind of boost regulator to keep it within its effeciency range. You could also setup your trans to shift within the powerband.

Then how come you make more power with 10psi rather than 5psi ? You'd think it would flow MORE air at 10psi .... ???

And why does a smaller pulley help performance and not hurt it? preasure would have to make up for the lost flow right?

The M90 flows that at those numbers, but when your throttle is partially opened, the M90 cannot flow the max for 5 psi.

I think to some extend.. maybe everyone is partially right...

Lower PSI with better CFM should make more efficient power..
Smaller pulley will raise PSI to make better power ( PROVIDING THERE'* NO KR )

And a lot of people have stated that if you go overboard and get smaller pulley like 3.2 or so for series II will make less power due to KR.. caused by overheated air, caused by more PSI.

Which comes back to density of air and volume the engine is ingesting.

I dont' know much bout it.. but this does make a good thread to follow up on. Need a thermo dynamic guru to chime in