Originally Posted by http://www.miata.net/garage/billa_sebring.html
The distributor of the Eaton blower, Magnuson Products, 3172 Bunsen Avenue #K, Ventura, CA 93003, (805) 642-8833, will modify original Eaton M-45 blowers to include the improved "*-trim" flow features and recondition the units for less than $300. The "turn-around" for this porting and reconditioning can be as little as 48 hours! "*-trim" is presently provided with all new Sebring units.
Info on the reasoning behind porting a supercharger:
Originally Posted by http://www.rtmmotorsports.com/Lightningcatalogue.htm
Eaton Supercharger PORTING now available from APTEN - click here!
YES! the Results are true! an extra 20 to 41rwhp on the dyno. 500rwhp is now Achievable out of your Eaton
There are plenty of other places on the net that show that porting a supercharger does have some advantages mostly reducing the temp of the intake charge allowing you to move cooler air (and hence be able to drop down pulley sizes with less chance of KR) not more air. And Bill, the last major change to the eaton'* was the abradable wear coating on the rotors. This is what makes the gen v able to move more air over a gen 3.