Yeah it's funny because at medium to high RPM's the OEM clutch fan is able to move a hellof a lot more air and energy-wise is more efficient on a CFM produced per HP consumed basis... BUT... The problem people don't seem to realize is that you don't even need the fan when you are moving, the air from the car moving usually is more CFM than you need (unless going slow). When you really need the fan's help is when moving slow or sitting still at idle... and guess what! Those times happen to be the times when your engine RPM is low so your OEM clutch fan isn't moving very much air! So basically the OEM fan much of the time behaves the opposite of what would be best for cooling the engine. The OEM clutch fan produces absolute shitloads of CFM... right when you DON'T need it!