Duramax Fan for stock shroud

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Erik the Awful

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If you look at fan blade spacing, you'll quickly realize the blades aren't equally spaced, and the blades are usually different sizes to keep the balance. The net result is that your fan is probably further out of balance than the factory margin of error.

But on a lightweight plastic fan it probably doesn't matter much.

If the fan blades are evenly spaced, it'll sound like a Cessna trying to take off. By using an odd spacing it breaks up the harmonics and makes the fan quieter.
 

0xDEADBEEF

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I would think in general that a clutch fan translates less wobble than a direct mounted fan and doesn't need to be as perfectly balanced. No data, just a feeling.

You could also use a bubble gauge to balance it like they used to do with tires, but you might have to make your own for something that light.
 

L31MaxExpress

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I think some of you are throwing the balance way out of proportion. The blade material is super lightweight. Just holding the blades they are also somewhat flimsy. At ~3,000 rpm there is absolutely no way that the blades are not distorting and twisting atleast on the ends. With plastic blades there is absolutely no chance that it ever runs perfectly balanced from the bend and twist in the blades alone. Years ago in this van I had the GM fan clutch let go. The clutch and blades wobbled on the shaft. I did not know what was causing it, but as you accelerated it felt like the whole front end was about to vibrate out from under the van. By comparison this is as silky smooth as the blade has always run. Given the fact I doubt the blade ever even turns 3,500 rpm, I am not overly concerned with it.
 
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454cid

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If you look at fan blade spacing, you'll quickly realize the blades aren't equally spaced, and the blades are usually different sizes to keep the balance. The net result is that your fan is probably further out of balance than the factory margin of error.

That's common with 5 blade fans, but I think the spacing is equal when you go up in blade count. I've never measured, but I think both my 9 and 11 blade fans are equal. Unless maybe the higher blade count, just makes it less noticeable. I'll have to look.

Edit: Nope, I'm wrong, you were correct, Erik the Awful.... the spacing is not the same. It' just not as noticeable on my 9 blade. (I didn't look at the 11)

If the fan blades are evenly spaced, it'll sound like a Cessna trying to take off. By using an odd spacing it breaks up the harmonics and makes the fan quieter.

I always wondered why. Sound never occurred to me. I should look at my Buick fan. I haven't really looked at it in years, since it's mostly obscured by the shroud.
 
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L31MaxExpress

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That's common with 5 blade fans, but I think the spacing is equal when you go up in blade count. I've never measured, but I think both my 9 and 11 blade fans are equal. Unless maybe the higher blade count, just makes it less noticeable. I'll have to look.



I always wondered why. Sound never occurred to me. I should look at my Buick fan. I haven't really looked at it in years, since it's mostly obscured by the shroud.

The GMT400 11 blade is offset. The 11 blade S10 fan has different straight blades and maybe 1 or 2 are offset slightly. I believe the 9 bladed Duramax is symetrical atleast to the eye without measuring. I think GM believed cooling on a turbo diesel designed to be worked hard overshadows fan noise. Not like a LBZ runs very quietly anyway. The Duramax blades were consistently the same width and length all the way around the hub, just never measured the spacing between them.

If your Buick is of the musclecar era, they usually had a 7 bladed fan. The old 7 blades were also asymetrical with offset blades.
 
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454cid

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The GMT400 11 blade is offset.

I didn't look at my 11 blade since it's on the truck, but I did take a look at my original 9 blade..... mostly for spacing not blade size. I was wrong in my thinking the spacing to be even. I saw two wider gaps, and I think two narrower gaps that were still slightly wider than the rest. It's just not as noticeable as it is with a 5 blade.

If your Buick is of the musclecar era, they usually had a 7 bladed fan. The old 7 blades were also assymetrical with offset blades.

Yes, defenetly that era..... 1969. It's been so long since I've even looked at the fan on the LeSabre that I'm not sure what it has. It's an AC car, so maybe the 7, but I believe 5 was also used. I'll have to look tomorrow, if I have time.
 

454cid

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If you look at fan blade spacing, you'll quickly realize the blades aren't equally spaced, and the blades are usually different sizes to keep the balance.

You're correct Erik, I checked my original 9 blade, and the spacing is indeed not even all the way around. It's not as apparent as it is with only 5 blades. I didn't really comapre the size of the blades.
 
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