Originally Posted by future370zzz

The Vortech SI impeller upgrade requires you to send the blower unit in and they replace it for you and check for any issues. Check out the Vortech site for complete details. Its about $350 plus shipping. Vortech Superchargers: Only Authorized Service Center | Vortech Superchargers

There is also the 928 motorsports impeller upgrade but I heard mix responses because some say it doesn't quite fit and others have made it work. I just went with OEM and called it a day.