clutch fans have a viscus clutch that spins the fan based against the resistance its working against
the fans generally spin the fastest at about 2000-3000 rpm
,so from idle to about 2500 rpm fan speeds increase along with but not directly related too engine rpm,
much above that rpm the resistance won,t allow the fan speeds to increase nearly as fast as rpms increase
so the clutch fans do soak up some engine power , but not nearly as much as a solidly mounted fan would have.
generally the more blades on a quality clutch fan, the better it cools
I generally used to look for the clutch fans of caddys and buicks as many will mount to chevy water pumps with minimal or no mods
http://garage.grumpysperformance.co...-mostly-over-looked-component.2756/#post-7161
most were available from salvage yards dirt cheap in years past you ideally want something similar to this
https://www.ss396.com/chevelle/FANK...MIqpLemIjB6QIVDtbACh1uzwYdEAQYBSABEgKWbvD_BwE
http://www.network54.com/Forum/215655/message/1066184641/Car+Craft+Cooling+Fan+Dyno+Test
don,t forget a matching fan shroud that matched the radiator and fan diameter,greatly increases cooling efficiency
Quote:
Originally Posted by
DjD View Post
No doubt you'll gain a few ponies with an electric fan but is it worth the extra expense? Here are some test results I got from an issue of Car Craft (May 2000) All these tests were run on Flex-a-lite brand fans except for the factory 4 blade. To baseline things the first dyno run was no fan at all but did include an
alternator.
No fan = 496hp
Electric = 494hp
Thermal clutch = 487hp
Nonthermal clutch = 485hp
HD thermal = 476hp
HP flex fan = 476hp
Stock 4 blade = 473hp
Low-profile flex = 466hp
One piece plastic flex = 460hp
OE replacement 6 blade = 449hp
You can see your fan choice makes a difference. The cost difference is quite a bit though and the electric fan they used cost $170 as opposed to the thermal
clutch fan at $66 and the nonthermal
clutch fan at $56 (remember these are all Flex-a lite products and the testing and prices are from May 2000) Also note that this test didn't go into cooling ability.
Both types of fans can keep your mill cool just like both std and alum radiators do as well. Alum and electric adds a wow factor under the hood but are costly compared to the alternative. I have no proof for you that one flows more air than the other at idle I do feel that most electric fans may actually restrict flow through the radiator and around the engine at higher speeds though.Electric fans also require your electric system to be up to the task and power relays and proper setup is critical. If power fails, the fans don't work. I know a fan belt can fail and cause a mechanical fan to quit working as well so it's a draw unless you are not very good with trouble shooting wires... I bring this up because you hear guys talk about wiring things so the fans run as soon as the key is turned all the time. This is because they couldn't figure out how to trouble shoot and fix the problem or just don't understand how it's susposed to work.
I am using Flex-a-lite's nonthermal clutch pn 5255 and fan pn 5718 ($56 through summit) I had my stock rad recored with the biggest core that fit between the tanks (under $200), a stock water pump and a Robert Shaw (Mr Gasket) 180deg stat ($10 - $12). I run about a 60/40 water to antifreeze mix with no other additives. I have sat in traffic for over an hr creeping along and my 383 didn't get to 190 degs. Moving it stays between 175 - 185 no matter how hot it gets outside.
My point, (as it so often is) is all about budget. If you are not on one your car ought to look and perform like the Mule. If you are on one you need to pick the most cost effective parts to get the job done so you have money for the rest of the project. Nothing worse than seeing a project take years and years and never getting completed do to lack of funds!!