[concobra]

Flex-a-lite's statement regarding the 4500 cfm is supported by: Permacool, Griffin Radiators, and others in the cooling business. To add to that the rule is better explained as you need 10 cfm for every cubic inch or hp made. Whichever is greater. Also the thicker the radiator the more need for air draw through it.

For what it is worth the only fan I found up to the CFM demands is sold by Vintage air and is called the Monster Fan. This was the only electric single fan that would pull the needed CFM. It works extremely well. My motor NEVER overheats and constantly runs between 160 - 180 degrees with the fan on. If fact last year I put in a 190 degree fan switch and even at over 100 degrees of air tempurature this fan cooled my motor down to 160 degrees in stop and go city traffic. I use it with a shroud offered by Vintage Air that best fits my radiator.

It's expensive but cheaper than warped heads.

I hope this helps.