Clutch fan options on my 340?

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71DodgeDemon340

71DodgeDemon340

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hey guys ive pondered this for too long, is there really a significant hp gain going from a mechanical fan to a clutch fan?

Whats my best option for a fan clutch? And can i use the factory style fan with said clutch?

Thanks in advance for any guidance
 
Ma MoPar stated and I have always heard from the local notable speed shops that a street ride that uses a fan should use a clutch fan. Electric fans are also very good if you need them and/ or don’t mind the extra wiring that goes with them. Not all electric fans are created equal ether.

Check this video out:
 
Yeah some interesting stuff, i remember seeing that episode, however i hate the idea of a electric fan, would like to retain some of the original look but also have the functionality of the clutch fan
 
My '72 340 Demon had a clutch fan on it,( not sure if original). It needed replacing and got one from NAPA. The replacment had a longer shaft and now clears the radiator by about 1/2". This is using an origional 7 blade fan. I believe that a clutch fan will draw less power when not engaged,( not sure how much).
Yote
 
Hayden makes a short shaft clutch fan for hot rods. Guys used to buy ones made for Jags, Hayden came out with one even shorter and stronger.
 
Yote, do you have the part number handy? Also will my 6 blade fan bolt up to the clutch?
Ive heard rumors about a fixed fan robbing 20 hp or so and the clutch only around 6hp

If i search for a hayden clutch is there any certain type i need to get?

Also is there any difference between thermal and non thermal?
 
Last edited:
There is a thermal and mechanical.

Self explanatory I think.

The engine masters episode shows the first dyno run with no fans at all. So there is a basic idea of how much power it does on THAT engine.
 
Yeah i know but i mean is there any benefit of one over the other? Will the thermal unit reduce rotation at higher rpm to reduce resistance on the engine?
 
As the temp goes up, the internal couplings disengage. The MP viscous unit has fluid inside that separates and moves outwards to allow the fan to uncouple and rotate free of the engine slower.
 
From my old invoice the part number is 271305 for $37. This was a couple years ago. IIRC the hub was slotted for four bolts. Not sure about your fan ,but if four bolt I would guess that it would fit.
Yote
 
I’m going through this now. I can’t find the Hayden number of the short shaft clutch. Anybody have that number ?
 
Hayden 2947

So how much will the thermal unit be engaged by at normal engine temps? My question is, is the thermal clutch better at high rpm more so than the fixed? Or will it be completely engaged at normal operating temp anyway?

I guess in theory the clutch fan will deliver only as much air as the engine needs correct?

I watched the engine masters again to refresh my memory but they were running the thermal unit inside and even stated that is was still cold and showed spinning the fan while the engine was off, so is that a bad example? It will rob less hp when engine is cold but what happens at operating temp?
 
Haven't noticed it on my Demon but on pickups I have had the fan would engage when needed
( sounded like a jet engine reving up) then noise would subside an the engine cooled. These fans will still revolve when not engaged but at a much slower speed.
Yote
 
Yeah what im trying to wonder is if its just better when cold at lower rpm vs the fixed fan or better all around, i mean with the fixed fan now i run 180 all day, maybe 190 in the summer. Im wondering if at that operating temp if the clutch is fully engaged or not.

Im wondering if the clutch fan robs less power only at cold temps or if it robs less power at operating temp vs the fixed fan
 
Good question, don't believe I have an answer for that. IMO a viscous fan should be variable speed depending upon temperature sensed even if engine RPM is constant. Maybe someone smarter than me can definitely answer this.
Yote
 
This make sense

Power Loss and Fuel Consumption
The 1970 Pontiac engineering brochure put it all in a nutshell with the following statement: “Fans. They cool. They also eat up horsepower. Conventional fans slurp up 20-24 horses at 6000 fan rpm. Flex fans, about 5 or 6. And clutch fans, about 4 or 5 horses. Take your choice. Why the difference? The flex fan blades flatten out at high rpm. Less resistance. Less drain. The clutch fan is thermostatically controlled. Cold, it runs no faster than 1000 rpm. Hot, it engages and picks up to 1800 rpm.
 
Per hayden.
  • Varies the fan speed with temperature of the air behind the radiator.
  • Engaged (high speed) operation provides maximum cooling.
  • Disengaged (low speed) operation provides fuel savings and noise reduction.
  • Greater life expectancy than a non-thermal clutch.
  • Briefly engaged at cold start-up.
  • Engages at about 170° radiator air temperature, (about 30° lower than coolant temperature).

The air temperature coming through the radiator is sensed by the bi-metal thermal spring on the front of the thermal fan clutch. It expands and contracts with the change in air temperature operating a valve inside of the clutch. When cold, the silicone drive fluid is pumped from the working area to the reservoir. When hot, the valve opens allowing fluid from the reservoir to be transferred to the working area thereby increasing the fan speed. The clutch disengages as the air temperature decreases, closing the valve and allowing the silicone fluid to be pumped back into the reservoir.
A thermal fan clutch is engaged on a cold startup because the fluid drains into the working area when the engine is shut off. The fan clutch will slow down shortly after startup as a result of a pumping action produced by a difference in speed between the shaft and the body of the clutch.

Most models are designed to duplicate original equipment performance. Some Chevrolet/GMC truck models are specifically designed to engage at lower temperatures than the original equipment parts that they replace.


Huh so if it engages at 200 degrees coolant temperature and i run 180-190 would it theoretically never engage? Or since its spining slower would allow for coolant temp to go above 190 in the same setup?
Right now on a spring day with the fixed fan it stays at 180, with the clutch fan would i see it fluctuate more? Could i see it reach 200 degrees before the fan is even fully engaged to cool it back down?
 
Dont like relying solely on a electric fan though.


Also i would need to get a new fan to go with the clutch, was factory a 5 or 7 blade and which is better?
 
This is the exact part you need. 340 clutch fan set up. No it's not for sale. Just a picture so you know what you are looking for.

downloadfile-21.jpg
 
That will set you back around $250 if you want exactly what is in the photo with correct part numbers.
 
Thanks 72, is there any issue with high rpm operation?

I know the aftermarket fans i have seen say max rpm is 4,000

Also is that setup you posted available new?

Also the clutch fans listed on summit dont say if they will accept HD clutches. One guy in the reviews said that it said not for use with HD clutches when he got the fan
 
Yes you can find it new. Use the part numbers on the parts and go searching. Or try Classic Industries or OER site
 
Dont panic. You can find both. Hemi pops up when you search for it. Yes they are the same. Don't worry.
 
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