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Discussion Starter · #1 ·
I have a 302 with a stock metal 4 blade fan that is about 1" from the 3 core radiator,the fan is also buried in the shroud. I seem to remember reading someplace that the fan should protude some amount out of the back of the shroud,in order for the cooling system to get the optimum use for haveing a shroud.Can anyone help me with the proper location and spacing on the fan ?
 

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I don't know about the shroud spacing, but the closer the fan to the core, the better it pulls air thru, which is what you are looking for.
 

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Discussion Starter · #3 ·
That's what I always thought as well,the closer the fan to the radiator the better.I'm not haveing any cooling problems the car runs at 195 degress in town and open road and on a hot day seting at idle in traffic never runs any hotter than 200 degress. I was just wondering bcause it has a shroud if the fan was farther way from the radiator if it would allow it to run as cool or cooler and make it a little easier to get to the fan bolts.
 

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Flex-a-Lite gives a certain distance away from the radiator when you are NOT using a shroud. But, when you use a shroud, the fan should be as close to half in and half out as possible.
 

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I will spare you guys the long version.

No more than .50” tip clearance and at least 2/3 of the blade tip should be inside the shroud.

With a properly fitting fan and shroud, the distance from the radiator is nothing to be concerned with.

_________________
67 Falcon 2dr sedan, 408W, C4 w/3500 stall, 3.80 w/Detroit. www.trailhed.com/Falcon.html
Anodize is making a comeback!

<font size=-1>[ This Message was edited by: 67falconer on 8/30/06 10:18am ]</font>
 

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Discussion Starter · #6 ·
I would be interested in the long version,it looks and sounds like it,s more of an opinion and a preference than it is a science or right from wrong way to have it instaled.
 

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I am curious as to why you would say it looks like an opinion?
Are you guessing or do you have any facts to contradict my statement?

I read the dimensions on a flex fan instruction sheet years ago and it has worked very well for me for many years.

As for the long version, it basically explains why you need a shroud and should use the dimensions that I mentioned. My long version isn't too special but explains it a little better.
*****
The fan tips do the majority of the work, which means you need a shroud to eliminate “tip wash”.

I have personally been involved with the engineering, installation, and testing of over 350 13' diameter fans as well as many other smaller units, and believe me tip wash is a major player in efficiency of a fan blade.

Its really not as much about installing a shroud to make the air come thru the radiator, as it is about making the fan, that is designed for a shroud, do the work it was engineered to do and you can’t do that properly with out a shroud. You will get air movement without it, but nothing compared to a fan with a properly fitting shroud.
A good set of dimensions for automotive fans is no more than 1/2” tip clearance and at least 2/3 of the blade tip or more should be inside the shroud.

Have you ever heard how noisy a flex fan can be without a shroud?
Take that same fan and properly fit a shroud around it and you can drop the noise level by 2/3. You will effectively be eliminating or stabilizing nearly all of the tip wash.

A simple definition of tip wash is nothing more than air turbulence caused by the blade tips. The shroud in effect stabilizes the turbulent air coming of the blade tip and allows the tips to “cut thru and move the air” in a smooth efficient manner.

Without a shroud, the trailing tips are hitting turbulent air caused by the leading tips, which causes noise and inefficiency.

Think of your fan as a simple pump. In a pump you have a blade and a housing. Without the housing you will have a blade that doesn’t do much of anything. You might get a little work from the blade but nothing like a blade with a proper fitting housing around it.

Shrouds make the blade efficient and also serve as a safety device!
 

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Discussion Starter · #8 ·
I was not meaning in any way that your reply or any of the replys was an opinion or a preference as much as it sounds and looks like from the answers I have been getting the position of the fan in the shroud is more of an opinion , preference or individuals choice.That's why any documented facts are nice to compare.no offense inteded at any one.
 

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Discussion Starter · #9 ·
it looks as if the article listed below would be as good as any to get good performance from a shroud set up .


Belt-driven Fans:
Determine the fan rotation
Look at the direction that the fan moves while looking at it from the front of the vehicle. If the fan rotates clockwise, it is a standard rotation fan. If the fan rotates counter-clockwise, it is a reverse rotation fan.

Ensure proper clearances 3/4" from outer edge of the fan blade to the shroud (with less clearance, engine movement could result in fan hitting shroud; more clearance results in lower efficiency).

1" minimum from the leading edge of the fan to the radiator core or closest obstruction.

1/2" minimum from the trailing edge of the fan to the pulleys and belts.
 

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Here is a pretty simple concept ... take it or leave it ...

Air does not move front to back out at the tips of the fan blades, it moves "Outward."

You need the fan PARTIALLY outside the shroud (we could argue about just how far out) but if it's outside the shroud the air can make natural movement out and away from the fan shroud ... If the entire fan (or too much of it) is inside the shroud the outward motion of air at the tips will simply cause turbulance inside the fan shroud which isn't productive to your radiators ability to cool.

I have always figured something in the range of 1/2 to 3/4 of the fan blades outside the shroud.

<font size=-1>[ This Message was edited by: MonsterMach on 8/30/06 11:18pm ]</font>
 

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Discussion Starter · #11 ·
I didn't want to argue any ones point if veiw on this.but it appears I've ruffled some feathers to the point of new replys are on the defensive,that was not my intention and I'm sorry.Monster Mach has given me a good explanation that I can understand. I need to get the fan blade back away from the radiator or out side of the shroud at least to the point that the outside tips of the fan are at least to the edge of the shroud.when I put the car together I had no shroud and was told to have the fan blade as close to the radiator as posssible. I'm using a 2" spacer on the fan now and the fan is 1" from the radiator.now that I have a shroud, I need to move the blade back away from the radiator in toward the engine,by using a 1" spacer I can do this. I do Greatly Appreciate everyones input even if it didn't sound that way,Thank you all for your help.
 

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Fans including auto fans move air from the entire blade, front to back, not just from the tips. The point of maximum work is the tip or the last few inches of the blade. I can prove it and have done so with a simple magnahelic gauge. This is how I set pitch on my large fan blades by mesuring air pressure over the entire blade with a magnahelic gauge. When setting adjustable blades, the blade is pitched up just under the point of stall as indicated by the magnahelic when a pitch is reached where pressure doesnt increase anymore.

Bob don't worry to much about ruffled feathers.
I love to debate these kids of things publicly with the hope that someone including myself might learn something new.
 

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67falconer

Just to be clear ... I realize "most" of the blade is pushing air "front to rear" but out at the tips, air is going "outward" ... We don't want that air creating turbulance inside the shroud.

The idea obviously is to create a Vacuum inside the shroud ... close tolerance between the blades and the shroud and proper placement of the fan (front to back) at the lip of the shroud are the important factors.

_________________


<font size=-1>[ This Message was edited by: MonsterMach on 8/31/06 9:43am ]</font>
 

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A fan blade with no shroud is terribly ineffecient, and takes more energy to turn. Why?

The outside 1/3 of the unshrouded blade is doing nothing but "churning" the air....

Look at airplane wings that have winglets, and take a look inside a jet engine where the fan is about .050" away from the cowl, and spins up to 20,000 rpm! Both of these applications increase the effeciency of the blade or wing as it moves through the air.

Same applies to the shroud. It doesn't need to be so close to the fan as to make contact, but the closer the better, and the blades should protrude out of the rear of the shroud, as long as the leading edges of the blades are inside the shroud by 1/2" or so.

It is not super critical, but with some attention to how the fan sits in the shroud you can really make some serious improvements in airflow and cooling effeciency.

Greg
 

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What about most OEM electric fans that have all the of blade inside the shroud?They seem to work good with no fan blades protruding outside the shroud.
 

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The main thing is to have the trailing edge of the blade outside of the shroud. With a flex fan, this means that the trailing edge must still be outside of the shroud even at high rpm when the blade angle is flatter.

If you;ll notice, most factory fans have the blade tips connected by a ring that acts like a shroud, and this "shrouded blade" is mounted inside an enclosure simply for ease of mounting and elimination of foreign object ingestion.

Greg
 
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