Clutch or not to clutch.
Just how much gain is there to be had by a clutch?
Ive heard the argument a direct drive fan is noisier , I'll call BS to that . Mine inst loud at all and I assure you I can not hear it windows open or closed, I surely cant hear it going down the road
There are no simple answers to your question as the size, pitch and number of blades all come into the equation. Normally a Clutch fan will have a more aggressive draw when engaged than a non clutch version but only drains the power when it's needed. The non clutched version on the other hand is a constant drain on the output of the motor whether it's needed or not.
I believe when people say a direct drive is noisier they are likely referring to an aftermarket flex fan some which can be very noisy.
If I remember correctly articles in the past have claimed a 7-10 hp difference on a healthy V8
A post over at A bodies only claims a 15 HP difference was verified on a dyno, I'd like to see the article as the only way to confirm that is if they used the same exact fan w and w/o a clutch and repeated the test several times
LINK TO A BODIES POST 
