No fan clutch

chromebumpers

solid fixture here in the forum
Staff member
I just noticed there isn't a fan clutch. Should I install one? I thought these clutches were pretty much universally installed on everything by a certain point in time?
 
Not everything Richard .
Leave the Factory Flex Fan on for now.
 
obviously the quality of parts, and the rpm and stress levels will effect the results , the cheap versions of flex fans have a rather well deserved reputation for turning to shrapnel after years of stress or if they get loose or hit anything that might cause an imbalance.
http://garage.grumpysperformance.co...-mostly-over-looked-component.2756/#post-7161

http://www.network54.com/Forum/215655/message/1066184641/Car+Craft+Cooling+Fan+Dyno+Test

ccfan1a.JPG

ccfan2a.JPG

better quality metal flex fans, when properly matched to a close fitting radiator shroud, can and usually do, move a huge increase in air flow rates over what can be expected from most electric radiator fans. this will generally reduce engine temps significantly and reduce loads on the alternator as you don,t need to run an electric radiator fan (s).
the problem's are that as the engine rpms increases much past 3500 rpm-4000 rpm they become a huge horse power wasting drag on the engine, and the blades by design tend to change angles to reduce the parasitic losses, that fan can require well over 35 extra horsepower to spin,
at over 4000 rpm, and thats a big problem, the flexing also eventually causes stress fractures in the blades and if used long enough over time the blades do occasionally come off and that can be a big problem as the blades fracturing instantly unbalance the fan, and shortly after the water pump bearings fail due to vibration related stress.
there are several sources for flex fans and quality and size , and designs obviously vary so shop carefully and avoid the cheap fiberglass versions,
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!!




READ
http://www.haydenauto.com/Featured Products-Fan Clutches and Fan Blades/Content.aspx

http://www.licorvette.com/Corvette Fan Clutch.htm

http://www.popularmechanics.com/cars/how-to/a302/1772922/

http://www.rockauto.com/genImages/93/haydenSD-HD-SVRD.pdf

https://www.haydenauto.com/en

and REMEMBER CHEVY
WATER PUMPS,
FAN CLUTCHES
AND
FANS,
ROTATIONAL DIRECTION

VARIES BETWEEN CARS
SO YOU MUST MATCH THE INTENDED APPLICATION FOR THE COMPONENTS BEING USED FOR ALL THREE COMPONENTS

https://m.summitracing.com/parts/der-19118

https://m.summitracing.com/parts/flx-1318

https://m.summitracing.com/parts/prm-83182
fanj.jpg


but there is a well proven and fairly inexpensive solution
installing a viscus fan clutch


fanclutchj.jpg

if you install a viscus fan clutch at lower rpms the fan spins at almost engine rpms, the internal hydraulic friction clutch keeps the fan blades , spinning but as rpms increase and resistance to the fans blades increase, the internal clutch allows some of the engines energy to push the fan, but slippage increases, so your fan may only spin at 3700rpm-4500rpm ( this mostly depends on the fan clutch design, fan loads and clutch age and condition) the fan clutches do eventually wear out, but its been my experience they are generally good for 6-7 years before youll find any significant wear.
use of a fan clutch can easily reduce the parasitic drag loses , by over 50% from those the engine would see without the fan clutch.
theres little doubt they move a good deal of airflow and help cool the engine effectively, yes thats an impressive looking and probably much more effective fan, , and while its a personal choice, if it was my car, Id have a clutch fan not a spacer installed, and a surrounding fan shroud around the fan blades, to further increase the air flow rate efficiency through the radiator fins. remember the object to effectively transfer heat from the engine coolant to outside airflow,
The use of the fan without a clutch hub, wastes some power,simply because it robs, your car of some potential peak power , through added drag, in its current config. compared to using a clutch fan hub. yet the cars cooling capacity, is not really benefiting from the lack of a clutch fan hub. adding a shroud forces the air to flow even from areas the fans not directly behind.

shrouders.jpg






https://www.rockauto.com/en/moreinfo.php?pk=340168...

https://www.autozone.com/cooling-heating-and-c lima...

Id go this route


Mark Bradley said:
I have been looking at fan clutches for my ‘68 Camaro and I am a big fan of using the factory parts as a foundational point.
That being said I wanted to share a few part numbers I have found and some useful links.
My goal was to convert the Flex fan to a GM 7 blade unit with a fan clutch.
The hard part was to find the correct clutch.The OE part number was 3946050.
Finding the OE part number was the key and from there I worked backwards looking for a heavy duty part with the same measurements.
Introducing...Standard Motor Parts (SMP) as one of the largest manufacturers of units and sell them under various brands (Hayden, 4Seasons, Murray, etc..).
Hayden offers a part number cross reference:
https://www.haydenauto.com/en

RockAuto happens to offer a dimension lookup table that I used to find a heavy duty part after identifying the replacement OE part.
http://www.rockauto.com/genImages/93/haydenSD-HD-SVRD.pdf

215046 is the SMP part number I have targeted.
It cross references to:
Hayden 2747
4-Seasons 36956
 
Last edited:
This isn't even a flex fan, just a fixed position hard blade. If this was a daily driver I would be installing an electric fan.
Its Ok.
All 1961-63 SD421 FACTORY RACE ENGINES USED THE SAME FIXED FAN.
405 HP Is actually closer to 550 Hp.
 
This isn't even a flex fan, just a fixed position hard blade. If this was a daily driver I would be installing an electric fan.
Its Ok.
All 1961-63 SD421 FACTORY RACE ENGINES USED THE SAME FIXED FAN.
405 HP Is actually closer to 550 Hp.
 
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