fan shroud, mechanical fan, fan location

WZ JUNK · April 21, 2005, 09:19:11 AM

I tried to do a search because I think we have discussed this before but the search would not work for me today.

I am building a fiberglass fan shroud and I need to know the correct depth to space the fan in the shroud. I have my own opinion but I want some unbias opinions to verify my thoughts. Help me out.

DRD57 · April 21, 2005, 10:31:19 AM

Quote from: "WZ JUNK"I tried to do a search because I think we have discussed this before but the search would not work for me today.

I am building a fiberglass fan shroud and I need to know the correct depth to space the fan in the shroud. I have my own opinion but I want some unbias opinions to verify my thoughts. Help me out.

I've always been told they should be centered right at the edge of the shroud. Kinda half in and half out.

Ohio Blue Tip · April 21, 2005, 10:40:12 AM

I'm doing a fan and shroud on my 34 and using a Walker shroud on the Walker radiator. I've been told and plan to have the fan one third into the shroud and about one quarter inch clearance on the outside. I've been told that the air should come off the fan at about 45 degrees for the best cooling. If the fan is too far into the shroud the air will pile up in the shroud and if the fan is too far out it will not pull the air through the radiator as well as it should. I could be wrong

HOTRODSRJ · April 21, 2005, 10:59:59 AM

I have some experience with this and I think can help.

The question is what is your shroud design and your blade design? Does it have an exit collar or just come to a round exit where the fan resides.

If you have a "tunnel" or collar that is round and extends from the main part of the shroud (like the old 70 era Monte Carlos and Grand Prixs) then you can put that blade anywhere inside that collar or tunnel for optimum performance.

If you have a real small collar or just a round exit to the shroud, then the fan should be 1/2 and preferably 2/3 of the way INSIDE the shroud opening. For example in the picture provide on the wifey's 69 ragtop....and even tho you cannot see the fan, it's perfectly 2/3 the way inside that shroud design with an inch of clearance all the way around.

I played with the Derale heavy duty fan in and out of the opening with the 2/3 position working about 25% better in airflow than anyother location. It is true if you get the fan positioned too deep, the fan wash will hit the backside of the shroud and produce eddy currents which are unproductive.

Jbird · April 21, 2005, 12:16:33 PM

I think this is what Steve means. This is my 84 Chevy PU. I installed the entire powertrain out of a 93 Caprice in it, even fan shroud and radiator. I had to make two 2" stands to raise the radiator up into the grille opening and flip the shround upside down. Now the 'CAUTION FAN' warning label cast into the shroud is visible from underneath the truck. It's amazing how much of the Caprice stuff worked on the truck, even the Caprice throttle cable hooked up like it was made for the truck.
Jbird

WZ JUNK · April 21, 2005, 02:02:11 PM

I remembered the Walker instructions saying 1/3 of the fan in the shroud like Ken mentioned but I wanted to have it farther in for safety sake. I am planning on making a fiberglass box for the radiator and then cast a fiberglass ring just bigger than the fan with some clearance to allow for engine movement. I can then position the two in the vehicle and attached the two pieces. I think I will make the ring large enough to enclose the fan completely.

Thanks for the help. I feel better about my plan.

Ohio Blue Tip · April 21, 2005, 02:42:24 PM

Steve, I sent you a PM.

Man I'm confused, Walker says put the fan 1/3 in the shroud, Flex-a-lite says 1/2 and Steve says 2/3. Without a lot of testing where is one to start?
I would think that there are many Walker radiators with Walker shrouds and Flex-a-lite fans out there.

My fans in stock.

WZ JUNK · April 21, 2005, 03:01:43 PM

Quote from: "Ohio Blue Tip"Steve, I sent you a PM.

Man I'm confused, Walker says put the fan 1/3 in the shroud, Flex-a-lite says 1/2 and Steve says 2/3. Without a lot of testing where is one to start?
I would think that there are many Walker radiators with Walker shrouds and Flex-a-lite fans out there.

My fans in stock.

This is exactly why I asked the question.

HOTRODSRJ · April 21, 2005, 04:20:43 PM

Quote from: "Ohio Blue Tip"Steve, I sent you a PM.

Man I'm confused, Walker says put the fan 1/3 in the shroud, Flex-a-lite says 1/2 and Steve says 2/3. Without a lot of testing where is one to start?
I would think that there are many Walker radiators with Walker shrouds and Flex-a-lite fans out there.

My fans in stock.

I don't know where Walker is getting their information and/or how much actual testing they are doing (I doubt any)...but 1/3 is not bad, 1/2 is better, but 2/3 is best and here's why.

Some of this depends on the design of the blades of the fan you are using too. A fairly square tipped blade will have alot of air roll off the tip as unproductive "eddy" currents and leaves unfettered air to go anywhere it wants. By placing at least 1/2 of the blade inside the shroud will set up a pressure barrier at the ends that holds more air on the blades to move in the correct direction. Same thing with 2/3 only a larger barrier and more controlled air movement. And, the more agressive your pitch on the fan blades, the deeper you want it in the shroud. I think the two manufacturers try to swag it for everybody regardless of fan type.

The reason you can't put too much of the fan inside this "open" type of shroud is that if enough of the fan blade cord is inside, the barrier will disappear again and all that air will roll off and actually wash against the backside of the shroud. So, I always recommend at least 1/2 and preferably 2/3.

Insofar as good fans to use, you cannot beat the Derale heavy duty series #17XXX series. See http://www.derale.com/flexfans.shtml for more info. Will outperform the big block air heavy duty fans and will give up it's bite at higher rpms. Good for 8000rpms and fabricated just like OEM....no flying blades or shrapnel to Dodge. The 17" version of this fan is on my wife's 69 Camaro with 425hp+ motor, air, and will set in Atlanta 100 degree traffic and won't come off the 180 degree thermostat cycling point! I highly recommend them.

WZ JUNK · April 21, 2005, 06:21:00 PM

It seems to me that fan shrouds are a weak area in street rod design. People spend a lot of money on their cars and then they either do not run a shroud or the shroud is improperly installed. I am frequently asked why a car is running hot. When you pop the hood to look, there is no shroud or the air is being recirculated back to in front of the radiator. When you try to explain what is wrong, they just look at you with a blank expression.

Dirk35 · April 26, 2005, 08:54:46 AM

Quote from: "WZ JUNK"It seems to me that fan shrouds are a weak area in street rod design. People spend a lot of money on their cars and then they either do not run a shroud or the shroud is improperly installed. I am frequently asked why a car is running hot. When you pop the hood to look, there is no shroud or the air is being recirculated back to in front of the radiator. When you try to explain what is wrong, they just look at you with a blank expression.

Mannnnnnnnn, Do I ever have the "Blank Expression" down!!! Im a real pro there!

WZ JUNK · April 26, 2005, 09:33:25 AM

Quote from: "Dirk35"
Quote from: "WZ JUNK"It seems to me that fan shrouds are a weak area in street rod design. People spend a lot of money on their cars and then they either do not run a shroud or the shroud is improperly installed. I am frequently asked why a car is running hot. When you pop the hood to look, there is no shroud or the air is being recirculated back to in front of the radiator. When you try to explain what is wrong, they just look at you with a blank expression.

Mannnnnnnnn, Do I ever have the "Blank Expression" down!!! Im a real pro there!

Yesterday evening I made the two molds to make this shroud. Today or tomorrow I will lay up the pieces. I plan to take some pictures of the process and post them. First thing today I have to take up some issues with Vintage Air.

flt-blk · April 26, 2005, 01:52:04 PM

What effect will a flex fan have inside a shroud?

Should I shoot for 2/3 inside with the blades flat (At RPM)?

WZ JUNK · April 26, 2005, 02:16:25 PM

Quote from: "flt-blk"What effect will a flex fan have inside a shroud?

Should I shoot for 2/3 inside with the blades flat (At RPM)?

I am going to place the whole fan inside a cirular tube like the factory shroud. Right or wrong this is what I intend to do. Safety wise I think this is best but it might not be best for cooling.

1FATGMC · April 26, 2005, 03:14:11 PM

Quote from: "flt-blk"What effect will a flex fan have inside a shroud?

Should I shoot for 2/3 inside with the blades flat (At RPM)?

If you are having cooling problems I would think hard about using a flex fan. I tried 2 on my truck and they just didn't cool in traffic or at idle. I went back to the stock fan.

Maybe there are some that work.

c ya, Sum