I honestly dont know why....I must check im using a 22 on the bottom but i definatly have a 48 ontop. I did some calculations somewhere a while back, i will have to look through my notes!

YOu are right though, when i changed my blade angle right back the cushion was a lot better and the engine ran faster.

If this is the case would just changing the bottom pully to an 18 tooth be a solution dropping the fan to approx 3.2Krpm?