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I have been running a 15" fixed fan with no shroud up until now with no problems. Looking ahead a little with my 440 build and not knowing what to expect, I just picked up an 18" fan to help cooling a bit. I was wondering about a fan clutch, whether to use one or not. I understand the operation theory, but is it necessary?





Using one depends on a lot of things. Some of the aftermarket aluminum rads that have thick cores, make it difficult to find a short enough clutch that will fit. The five blade mopar one works fine if it will fit, but you will need a large rad as I have found they don't move enough air at idle for some combos.

This stuff all has to be done as a package. Usually the pully on the water pump is a little smaller than the crank pully to give it a little over drive speed. The stock set up using a large 18" or bigger fan with 6 or 7 blades. The smaller pulley helps with cooling and not performance, and the opposite is true.

I would start by looking at your application (lots of idling, hot weather driving-large fan, big rad, shroud, small waterpump pulley-short trips, limited use, street strip car-larger pulley, mopar fan clutch/flex fan)
Compression plays a big roll in this as does timing.

I run a solid 16" fan with a shroud and a 22" aluminum rad, 1:1 pulleys in a Road Runner with a 650HP 472 Hemi.) It's a street only car and in the heat it sits around 180-185, however if it idles in the heat longer than 15 minutes it will start to heat up, but it cools right back down once it's moving