"...The Derale heavy duty flex fan is a newly designed series that outperforms any clutch fan assembly and does not have the downsides of the old designs. It features full support blades, hardened metal centers and full rivot stainless steel blades (not aluminum or steel). They are good for over 8500rpms and will NOt fling blades and pull about 33% more air thru the system and use a fraction of the hp up top.
Fixed bladed fans can take up to 40hp+ to fling around and even 30ish with a clutch. The new technology Derale takes less than 7hp at full tilt because it gives up it's "biting" attitude at high rpms...."
One thing to consider, if you have enough room between the radiator and fan, and you can fit one, you might be able to put a slimline electric fan inside the shroud, between the rad and mechanical fan (my Dodge truck uses this setup). Spal or Derale make some 2" or 2.5" thick electrics that might help with the idle airflow issue.
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