How many blades does the best GM mechanical fan have? I got one with 7 yesterday.. - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-04-2012, 11:18 AM
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How many blades does the best GM mechanical fan have? I got one with 7 yesterday..

I took one with 5 blades off, and plan on putting the 7 blade on.... any benefit here?

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Old 09-04-2012, 11:21 AM
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By best I mean moves the most air! Don't really care much about noise at the moment.
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Old 09-04-2012, 03:53 PM
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I've always used the HD 7 blade GM fan with the clutch too.
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Old 09-04-2012, 06:36 PM
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you can also add a shroud and a chin spoiler and use a rad seal kit from nissan path finders
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Old 09-04-2012, 07:59 PM
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There are also three versions of the Hayden fan clutch - standard, heavy duty, and extreme duty. If you look at the Hayden web site they have some documents that explain when each type of clutch will lock up and how the lock-up mechanism works.

Bruce
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Old 09-05-2012, 03:38 PM
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Thanks, I bought a regular duty imperial fan clutch because no matter where i looked i couldnt find a heavy duty one for the buick 231 v6. I took the 7 blade fan off a 350 chevy truck at pick n pull and im just wondering if its actually going to move any more air than the 5 blade i took off....
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Old 09-05-2012, 03:41 PM
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Quote:
Originally Posted by vinniekq2 View Post
you can also add a shroud and a chin spoiler and use a rad seal kit from nissan path finders
rad seal kit? For sealing the shroud to the radi? Im gonna use the shroud that came with the truck but the fan is about an inch out of it with a spacer and long shaft fan clutch.
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Old 09-05-2012, 04:00 PM
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There are equations/formulas (google it) to calculate the CFM of a fan.
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Old 09-05-2012, 06:15 PM
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rad seal kit: seals the air gaps where the rad mounts to the frame.Only allows air to go through the rad. The air cannot go around the rad,only through it
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Old 09-06-2012, 11:44 AM
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Assuming the 5 and 7 blade fans have equal blade pitch and length I would say the 7 blade will move more air?

bt
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Old 09-06-2012, 11:55 AM
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Quote:
Originally Posted by beertracker View Post
Assuming the 5 and 7 blade fans have equal blade pitch and length I would say the 7 blade will move more air?

bt
Diameter, pitch, number of blades and RPM's determine the CFM.
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Old 09-07-2012, 08:53 AM
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By the looks of my research the 19" 7 blade fan is one of the best GM made. Apparantly the 5 blade diesel fan is better..
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Old 09-07-2012, 05:55 PM
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So which is really the best?
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Old 09-08-2012, 04:39 AM
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Diesel fan probably has more pitch for lower rpm use.
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Old 09-08-2012, 06:57 AM
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Quote:
Originally Posted by 0trbo4myCHEVUICK View Post
I took one with 5 blades off, and plan on putting the 7 blade on.... any benefit here?
Expect most 7 blade fans to pull more air than a 5 blade fan- providing there is sufficient flow available through the grill/radiator(s). If there isn't, there can be a stalling effect.

For best efficiency fans w/the capability to flow large amounts of air should be used in conjunction w/a fan clutch to allow it to partially free wheel at speeds above where the fan is required to get air through the radiator; some vehicles will have enough airflow through the radiator at speeds as low as 30 mph that the fan isn't needed. This will vary by vehicle due to the grill and air inlet design, etc.

Bottom line is to run only as much fan as is required to cool the engine under the worst conditions it will encounter and no more. If it was cooling OK w/the 5-blade, unless the 5 blade fan had unusually large blades or severe pitch, it should require less energy to spin it than the 7 blade- and would be the "better" choice.

That said, it still comes down to diameter and pitch- even a 7 blade fan can use less energy than some 5-blade fans. 4 blade fans shouldn't be considered unless originality is important or the cooling requirements are trumped by energy savings. In such a case, an electric fan (and even water pump) might make more sense.

Proper positioning of any fan inside the shroud is also important. Less fan is needed when the rest of the cooling system is up to par. More on cooling systems, etc. here.
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