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Old 05-09-2006, 07:42 AM
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building a fan shroud - need help

I have a custom radiator and belt driven 17" fan in my 65 Chevelle 2-dr Wagon. I have built a custom fan shroud, but want to make the fan depth optimal for air flow.
I have about 1/2" clearance around the fan and currently have the "tube" part (or the part that surrounds the fan) at the full depth of the fan blades.
Picture an 18" pipe with a 17" fan in it. The pipe part butts up to a contoured box that fits the shape of the cooling area of the radiator.
Does anyone know what fan depth will give me the best air flow?
1. 1/2 the width of the fan blade
2. full width of the fan blade

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Old 05-09-2006, 09:35 AM
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I have always been told that getting the full width of the blade is best for air flow AND safety. I have done a few where all we could get was 1/2 the blade width and they seem alright. I think that having the front part of the fan shrouded is more important than the back if air flow is what you are after. Sometimes this is hard to attain because of clearance issues.
That is what I believe to be right.

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Old 05-09-2006, 10:10 AM
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Either way will work fine.
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Old 05-09-2006, 10:29 AM
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1/2 or less is better.

Picture the air flying straight off the tips of the fan blade like water. Will this airflow go back into the shroud and go forward to be recirculated, or will it fly rearwards toward the engine? Once the fan moves the air you want it expelled out the rear.
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Old 05-10-2006, 10:32 PM
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Thanks for the advice. I made a shroud out of 1/8" ABS, and it came out great. Heat forming this stuff is easy, and I was able to make a contoured shroud that fits the entire radiator cooling area, then comes to a round hole where the fan is. The part that encircles the fan goes on first, then you put the box part on and bolt the tube to the box. This allows for a deep tube that is the depth of the fan blades, while giving room to fit it in the car without disturbing the radiator or fan.

One "discovery" about the tube portion. I had used a flat strip of ABS, bent into a circle. It looked great and made a perfect circle, but when I glued the mounting tabs on, the glued spots softened the strip and caused the circle to distort and crack at one junctions. I will make it over again, but this time I will heat form the circle using a round barrel, so there will not be all that tension trying to be straight.

I will make a compromise between a full blade width and 1/2 blade width, adding more width at the top half for safety.

It only took about 3 hours to make this and it truely is a custom fit, so I feel it is well worth it.
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Old 05-12-2006, 12:58 PM
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Where did you get the ABS plastic to make your shroud? I'm thinking of custom making one for my truck as my "Bling-Bling" shroud is basically worthless
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Old 05-12-2006, 01:12 PM
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building a fan shroud - need help

Thanks for the info. When you have it finished post some pics. Also let us know how it works.
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Old 05-13-2006, 07:32 AM
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ABS supplier

I got three big sheets of 1/8" ABS from a plastics supply company just outside of Philly. I could not find the receipt, so I don't have the name, and I remember it being kind of hard to find them, but I think I found them when I started looking for plastic sheets instead of ABS sheets. Turns out they sell all kinds of plastic sheets.

I bought three sheets because I am making the interior of my 32 Tudor with ABS, kinda like rod doors, but custom formed to work around stuff like my A/C dryer, the computer, and custom window switch mounting. I did not like any of the "default" Rod Doors arm rests.

I fired up the engine yesterday with the new shroud in place and it worked out great. At a 600RPM idle, it sucks a dollar bill up to the radiator from about 5" away.

My remaining concerns are that I may have the clearance between the fan and the shroud too tight. So far when I rev it, there is no contact, but I don't have a functional clutch in the car yet, so I can't test it under a load. The other concern, which I will probably just change, is that I only have four mounting tabs around the round part. I think I will add another four.
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Old 05-13-2006, 09:23 PM
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That shroud looks good. I'll probably start doing some google searches and see if I can find some plastic
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Old 05-13-2006, 10:59 PM
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I read somewhere that the factory fan blades should be 1/2 inside the shroud.
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Old 05-14-2006, 12:06 AM
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building a fan shroud - need help

Thanks for the pics. Glad to hear everything is working out. The two piece design is a great idea. Would you have a pic of the whole unit out of the car?
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Old 05-14-2006, 12:34 AM
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If you're going to remake it, would it be possible to make the round part with the mounting tabs cut into the pattern? It would make it possible to bend the tabs outward and mount inside the flat part so that all you'll see is the fasteners from the back side (black carriage bolts or rivets would look good).

Looks great the way it is too though.
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Old 05-14-2006, 09:30 AM
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Pattern question and addtl pictures

The only issue with making the tabs part of the round part pattern, is that the easiest way to cut 1/8" ABS is to score it with a carpet knife, then bend it on the score line. It snaps with a nice clean break on the line. This would not be possible if there were tabs to work around. Of course it cuts pretty well with a saber saw, but you should use a variable speed saw so as not to create enough heat to melt it as is cuts. If you cut it with a saw, you can clean up the cut edge with a DA sander.

ABS is form able at around 325 degrees. I use a flared propane torch to get heat in the material. You have to be careful to try to get it even.
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Old 05-14-2006, 10:39 AM
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Circle track race cars use a flexible plastic for skirting that comes in 4 x 8 sheets or rolls about 18" wide, various colors. This has worked well for shroud material and for air gap seals/ air flow directors between the bumper and lower core support, etc.

I prefer adapting some factory made shroud and mounting with stainless steel tabs installed with stainess bolts.

Experience has shown me that very little fan inside the shroud is better.
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Old 05-14-2006, 10:47 AM
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shroud

very nice! Thanks for the info and photos. Bill
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