Originally Posted by
SMazza
The main difficulty with M90 blowers is getting the air in so the rotor cavity is filled. These particular blowers (GM Gen 3 and Gev 5) have pretty generous inlet ports to begin with, so the main problem is out of the way already.
If you compare the inlet ports on these blowers to the early M90s as used on the Thunderbird SC, you will see how much the inlet has grown over the years. Aftermarket products like the Magnum Powers MPX case have gone even bigger on the inlet that these blowers ... but those are designed to be spun very fast and give major high-RPM boost. There is a trade-off between minimizing boost leakage at low RPMs and maximizing airflow at high RPMs, and the MPX is skewed toward maximum performance.
Here is how to tell how far is too far. At the point where the leading rotor opens to the outlet port, the trailing rotor had better not be open to the inlet port. Otherwise, the pressurized air in the LIM will force air back out the inlet port. So that is the key thing to check.
Don't worry about the two small silencer ports ... they might let a small amount of air bleed back from the LIM, but it is by design, to keep the blower less whiny. Old people buy Regals, you know.
As for beveling the outlet port: Don't bother beveling the edge facing you. What would it do, help the air make the turn out of the outlet and shoot to the sides of the case? That doesn't make sense. Beveling (or filleting) the edge on the inside of the case is a good idea. It will help the air make the turn out of the case. Removing the bolt bosses (or not) is up to you. At a minimum, remove a little material to smooth out the airflow from the backside of the bosses out of the case.
The other problem that the early M90 had was control of the rotor clearances. The coated rotors in the second generation helped that issue, and the Gen 3 and Gen5 benefit from it.
