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Discussion Starter #1
1970 Mach 1 with 351 Cleveland

My fan sits too far into the shroud. It doesn't pull enough air at idle and the engine gets progressively hotter if the car is not moving.

I want to install a shorter/low-profile fan clutch to move the fan back a bit. It looks like the Hayden 2947 is the low-profile clutch, but I'm not sure if it will work with my fan. I have a 6-bladed fan. Does the Hayden 2947 work with a 6-bladed fan, or does it only fit the 7-bladed big-block fan?

Thanks.
 

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As long as the bolt holes are in the correct place it should be fine. Get the tape measure out & go to work.:


  • Fan Clutch Overall Height "IN":2.71
  • Warranty:1 year/12,000 miles
  • Mounting Hole/Stud Qty:4
  • Bolt Thread:5/16 in - 18
  • Clutch Type:Thermal
  • Color:Raw Aluminum in Color
  • Description:Fan Clutches
  • Drawing Type:C
  • Duty Rating:Heavy Duty
  • Fan Bolt Circle "IN":3.25
  • Fan Mount Dia. "IN":2.62
  • Fan Mount Height "IN":1.09
  • Material:Aluminum
  • Meets or Exceeds OEM Specs?:Yes
  • Mount Dia. "IN":2.59
  • Mount Type:Flange
  • Mounting Hardware Included?:Not Included
  • New or Remanufactured:New
  • Original Equipment Replacement?:Yes
  • Overall Dia. "IN":7.2
  • Performance Rated?:Yes
  • Pilot Depth "IN":0.56
  • Pilot Dia. "IN":0.75
  • Rotation:STD
  • Style:Heavy Duty
  • Type:Thermal
 

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The Hayden 2710 or 2711 are the two that pop up in application guides for these year cars. Attached the fan clutch section of the Hayden catalog so you can compare dimensions.
 

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IIRC, there are two different fan bolt circles, 3.25" and 3". On the 2947 clutch the fan bolt circle is 3.25". If your fan has a 3" bolt circle, I suggest you use the 2711 clutch. Note the fan clutch shaft on the 2947 is really short so there isn't a lot of room to tighten the bolts and an open end wrench turned 1/8 of a turn at a time is in your future !
If you don't have a local vendor for the 2947, I found it at Summit Racing.
 

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Discussion Starter #8
Don't use bolts, use the stud kit. Most parts stores have them on the shelf.

What is the advantage of using studs over bolts? I've seen what happens when a fan disconnects from a water pump, so I'm pretty paranoid and currently have grade-8 bolts with Loc-Tite securing my fan.
 

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What is the advantage of using studs over bolts? I've seen what happens when a fan disconnects from a water pump, so I'm pretty paranoid and currently have grade-8 bolts with Loc-Tite securing my fan.
Ease of installation - easy alignment and no juggling parts trying to get fan, pulley and water pump lined up with a bolt. Never had issues with fan coming off, ever. Just about every OEM used this method prior to threaded water pumps.
 

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Discussion Starter #10
My fan bolt circle is 3" so the 2947 won't work. It has a 3.25" circle.

The 2711 has the correct 3" circle bolt pattern, but it looks like it's not low-profile. That might be what I currently have installed.

2947 height is 2.71"
2911 height is 2.98"

The 2947 is the only low-profile clutch I can find online. Not sure where to go from here.
 

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Discussion Starter #11
Further research suggests I might get more fan blade clearance by installing a different fan shroud. I ordered the shroud from NPD. They have another shroud which is for A/C-equipped cars. It appears to be a bit shallower in the picture, but there isn't any info about that on the web site. I might have to call them during the week and ask if they can give me the depth measurements of each shroud.

I'm sharing all this in case some other poor schmuck like me has a similar problem somewhere, some day.
 

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Measure from the water pump pulley flange to the radiator core. That is the space you have to work with. I used a 2711 on a '67 big block 390 with a 4 core (379-4) Modine radiator and the clearance was indeed close. IIRC correctly, I had a bit more than 1/2" between the fan and the radiator. Several years back I was down at Knott's in 90 degree weather, stop and go traffic, with the A/C blasting nice cold air in my face, and the temp gauge never rose above mid point.

On the '70 Cougar with a 351 Windsor i recently upgraded to the 2947 and the big block fan (18-1/4" diameter). On the hardware, I used ARP bolt kits for the fan clutch and the fan. Before the upgrade, the Cougar had the correct fan shroud and a small diameter flex fan. It ran about 180 degrees on the highway with a quick climb to much as 215 when stopped or stuck in traffic. Yesterday morning I was stuck in beach traffic for about two miles with the ambient temp in the high 90's. Temp gauge moved up from mid 170's to almost 200 dropping immediately when I was able to exit the freeway and get moving again. The space between the water pump flange and the radiator is about 4-1/4" and the fan blades are about 1-3/4" from the radiator.
 

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If the CLUTCH clears the radiator and the issue is the fan BLADES, perhaps a fan with more blade offset will work?
 

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Discussion Starter #14
If the CLUTCH clears the radiator and the issue is the fan BLADES, perhaps a fan with more blade offset will work?
I did not know an offset fan was an option. Thanks, Bart. I will look into that as well as a different shroud.
 

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Discussion Starter #16
I talked to West Coast Classic Cougar. They seem to be very knowledgeable on this subject. They recommended the 7-blade 428 CJ fan and clutch, so that's what I ordered. I'm hoping I have enough shroud clearance.
 
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