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Discussion Starter · #1 ·
Looking into getting a new fan clutch setup, but unsure what to get and where to get it...

I had planned on the 7-blade with the Hayden #2747 HD clutch, but when I search some resto suppliers, I see a 7-blade fan that has curved blades, but NOT curved tips. I thought the 772 had curved tips as well...


Then looking at the Ground Up website, they offer a 7-blade for a short water pump setup, and the blade tips are curved (as well as the entire blades).


1964-1968 Chevelle Curved 7 Blade Cooling Fan for Short Water Pump

BUT, since this is listed for a pre-69 short water pump setup, it will NOT fit the Hayden HD clutch... For the short water pump setup, Hayden does NOT offer a HD version, just a standard duty version...

7-blade for the long water pump, from Ground Up
1969-1972 Chevelle Cooling Fan With 7 Blades For Long Water Pump (17.5 Dia)


Not sure what difference the curved tips make, but I'd hate to get the standard duty, and later wish I had gone HD...


This is NOT a resto, so I don't care about being 100% correct ( "correct" would be the 5-blade clutch fan, which I have several). I would like to look fairly "OEM".

While it does NOT matter, this will be used in a short waterpump setup. Years ago on another Big Block/short pump Chevelle, I used the later 7-blade and HD clutch, so I know it all fits, but I recall curve tips, but years ago...
 

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Why are the blade tips on a 3947772 curved ? Any takers?
On my one owner 70-LS-5/M-22 I have often wonder why myself. By accident I figured it out. AFTER I sawed a small hole in my factory 1970 plastic fan shroud on my driver using a non 772 blade.
A Factory plastic fan shroud and the 772 blade are designed to be used together.
The simple answer is:
The inside radius on the factory fan shroud matches the radius of the " CURVED " tips on a 772 blade. So, When your engine torques up a bit, The engine may move a bit, This could start the sawmill into action. It did on my B.B. -70 Driver. I got over being P!$$ED, :surprise: Patched up the shroud and installed a REAL 3947772 blade.
Do you really think G.M. would waste the time and dollars to design this blade with curved tips just for FUN ???? I do believe some items on G.M.- Ford & MOPARS are " PURPOSE BUILT ". Yes, Other blades fit & function well.
My LS-5 has the VO-1 Cooling system. I made a perfect copy of the VO-1 system for my 468 driver, So far 37.000 and 7 years NO COOLING issues. :thumbsup:
Bob
A 3947772 is an " Engine FAN "---- Not a Football Fan. Hey Nick, That Orange Paw, GOTCHA !
 

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The difference between the standard duty (2710) and the HD (2747) as far as the fan is concerned is the bolt circle. I'm sure everybody knows that, and the HD fan/clutch set-up will fit both long and short water pumps, dimensions are real close. On my short pump BBC I used Derale fan (17118 6 blade) and Hayden HD clutch (2747). I'm still having cooling issues, but thats another story.
 

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Hey Mike,
Good info, helped answer some questions I had about this setup. Don't assume everybody knows. You just taught me something new!
Thanks, Terry :thumbsup:
 

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Discussion Starter · #5 ·
The difference between the standard duty (2710) and the HD (2747) as far as the fan is concerned is the bolt circle. I'm sure everybody knows that, and the HD fan/clutch set-up will fit both long and short water pumps, dimensions are real close.
Yes, I know the HD clutch will fit both long and short water pumps... But I don't really want to buy a new fan blade and then need to redrill the bolt circle on that new blade, but I also recall the center hole of the fan differs (which locates the blades, hub-centric... But so far, the pictures I have seen for the long water pump fan blade don't show the curved tips... Like Robin stated, there is probably a reason why GM bent the blade tips... I figure a little overkill now ( 2747 HD clutch) is much better than running into cooling issues with standard duty parts ( 2710 standard duty clutch) and having to buy other stuff...

BTW, here are Hayden's "specs" for their Standard duty and Heavy Duty clutches;
Hayden - Fan Clutches and Fan Blades

Standard duty spins the fan 60-70% of the shaft/water pump speed when clutch is engaged...

Heavy Duty spins the fan 70-90% of the shaft/water pump speed when engaged...


Here's the 64-68 blade, which ONLY fits the standard duty clutch... Note the curved tips...

If Hayden offered the HD clutch for this application, thats the route I'd probably go... But Hayden doesn't...



Here's the 69+ offering... This should fit the HD clutch, but the blade tips aren't curved. If I KNEW performance would be the same, I wouldn't care...


I haven't searched everywhere, but numerous places offer this straight-tipped blade...


GM has a replacement for the 772, but IIRC, it also had the straight tips...
 

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I seem to remember reading somewhere that GM went to curved blade tips for noise reduction. When fully engaged, a 772 fan makes a racket at higher RPMs.
 

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I seem to remember reading somewhere that GM went to curved blade tips for noise reduction. When fully engaged, a 772 fan makes a racket at higher RPMs.
Yes, the curved tip was to reduce noise...I have heard this also. The Derale 6 blade I mentioned above has both bolt circles so it can be ran with std or HD clutch (I have used it with both clutches). I too could not find a curved tip 7 blade at the time so I settled on the 6 blade. I would really like to compare a curved 7 blade side by side with what I am using.
 

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Not sure about your year car. The 3947772 Fan blade was designed for the 70-72, 69 ? for the 3:31 Rear end. The 70 LS-6s also used the 772 fan blade with 3:31 Rear. NOW if you ordered the factory 4:10 rear gear, The 3947772 fan blade was replaced with a different number fan blade , I forget that number. Same size, BUT a different pitch on the blade.
Its all about moving XXXXX number of Cu. Ft. of air per. Min. through the Heat Exchanger or Rad.
Bob
 
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Discussion Starter · #11 ·
Not sure about your year car. The 3947772 Fan blade was designed for the 70-72, 69 ?...
Bob,

This will be going on my '66. As I mentioned above, I have run the 772 on my other '66 convertible, so I know it will fit and function, but I sold that car about 10 years ago... At the time I was was building it, I was told the "newer" (69-70+) 7-blade GM design would be better than the stock 5-blade clutch that came on '66s (made sense to me). All this fit in the factory '66 fan shroud with the stock radiator and short water pump setup.


I had a newer clutch for the 5-blade, but I found it wouldn't fit the "new" fan, so I had to buy a new clutch too...

I found a few places tonight offering the curved tip 7-blade (repro)... About $110 and up... the not-curved tip blades I have found for around $70+...
 

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Not sure about your year car. The 3947772 Fan blade was designed for the 70-72, 69 ? for the 3:31 Rear end. The 70 LS-6s also used the 772 fan blade with 3:31 Rear. NOW if you ordered the factory 4:10 rear gear, The 3947772 fan blade was replaced with a different number fan blade , I forget that number. Same size, BUT a different pitch on the blade.
Its all about moving XXXXX number of Cu. Ft. of air per. Min. through the Heat Exchanger or Rad.
Bob


3976064 LS6 with 4:10. Dates M69 and E70. >:)
 

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I recently bought a repro 772 fan blade from Modern Chevrolet- Classic Muscle. It cost me $110 with free shipping. I attached it to a Hayden 2747 fan clutch. The fan has 3947772 stamped on each curve tipped blade. It is not a GM part, it has a Made in Taiwan sticker on it. Terry
 
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