is there any ratio for intake : exhaust fans?

using cm 690,i got 2 intake fan(well,1 is behind d mobo,cant qualify as intake rite) n 4 exhaust fans...is this d optimal setting?
seem d intake fan not functioning well as its blocked by hdds n cables
opinion n suggestions plz

This post has been edited by shajack: May 17 2010, 07:46 PM