Technical Adventures in Fan Shrouds, or Does Anybody Know What an Optimum Design Should Be?

OK, I finally bought the parts needed to swap out the noisy-ass flex fan in my avatar. The car currently doesn't actually overheat, but will tend to get warmer during parades or on real hot days. There is no shroud on it now.

I'm swapping to a clutch fan, matching size (17") and bought a universal shroud kit for better efficiency. The kit shroud is 2" deep, but I have room to make it much deeper. But how deep is good?

The existing fan has a 4" spacer to get it reasonably close to the core, but the clutch is going to locate the new fan back from the radiator about 2.5" more, so that puts the fan outside the shroud if I install the shroud against the radiator. I'm not sure that using a spacer with the fan clutch is a good idea and want to avoid this.

I have two options; extend the shroud back, which is no big deal as I have to do some monkey-motion to mount it anyway. This creates a larger plenum which I would think would promote more even air flow, possibly at the cost of reduced air velocity. Or go closer to the radiator with the main shroud, and install an additional round shroud extension around the cut-out for the fan. The shroud kit has the parts to do this. I'm leaning towards the first choice, but do want this to work right.

And how critical is it to seal around the edges of the shroud?

Thoughts, opinions?

 

Put the fan on, clutch and all. Extend the shroud to meet the tip of the blades, or even have the blades (centered) with the outside lip of the shroud.......
The clutch will be "farther into" the shroud, but the blades and overall lenghthening will be determined by spaceing, and giving yourself room from clutch to radiator.

 

Create negative pressure over the core of radiator. Fan can be 2' rearward, just draw.

 

I have used a Walker radiator, fan and shroud on my '40 coupe for over 25 years with no problems in 95F temps and in traffic. The engine is a 327 FI (375 HP) with a few mods, good set of headers (Jet Hot coated), stock GM water pump.

Walker told me to seal up the shroud perimeter to prevent by-pass. The 17" fan is located so the blades are 1/2 way into the shroud (as recommended by Walker), about 1/16" clearance between the blade tips and the shroud.

 

What he said!

 

Distance to the core isn't as critical as axial space between fan and shroud. The fan should be located in the shroud about 3/4 of the way IIRC. If cooling of the car is not an issue maybe none of this matters as it is about optimizing airflow overall and creating even airflow through the radiator.

 

Make sure the shroud is as tight as possible on the radiator to avoid drawing in under hood hot air. After that extend the shroud back until 1/2 way or so covering the depth of the fan. Look at what GM did on the small block Monte Carlos of the early to mid '70's. Their shroud extension was almost the length of the Lincoln tunnel! I had one back then and lived in the low desert were summer was 110-115° during the day and a balmy 95-105° at night and we kept the a/c on all the time and had no overheating problems.

 

If you still have overheating problems take off the clutch and run the fan direct drive.

 

Thanks guys, I didn't figure this was rocket science but I'm also not known for my good luck either so covering the bases is my standard modus operandi...

 

1/2" from the fan diameter and split the blade in and out worked for me.

 

I use a engine driven 17" steel blade fan on the wagon & my deuce sedan and they never run hot, btw I don't have shrouds on ether one.

These things move a lot of air.




I have used the aluminum flex fans in the past and I always had problems with running hot regardless of how good my radiator was. HRP

 

One other thing that helped me was sealing the area above the radiator and mount to the hood. This forces all the air thru the grill into the radiator. My car had them stock depending on the where the car was originally sold. Mine was missing; I used a rubber seal that fit on metal I found at McMaster Carr. Also made a big difference.

 

My 63 Belair 2 door post car, original Harrison radiator with a 2006 Toyota Camry dual fan set up. Runs cool A/C on or off. Lots cheaper then a after market set up that works great. Fits the Chevy radiator like i[t was made for it.ATTACH=full]4226856[/ATTACH]a

 

I always herd fan should be 2/3rd's in and 1/3rd. out of shroud...............
HRP, Got a part number on that 6 blade you posted? Thanks!

 

I vote mechanical fan at least partway into shroud...

 

Cooling effect is also largely affected by obstacles in the engine compartment that diminish fan efficient. Getting that hot air out of the engine compartment as efficiently and as quickly possible is also very important. I read a very good article on this once, but I'll never ever likely find it again.
Moving slowly in a hot environment will push any good cooling system to the test, especially if the a/c is on as heat rejected by the condenser negatively impacts radiator cooling performance due to higher air inlet temp. A belt driven fan will be operating below optimum conditions, so airflow through the rad is reduced. The compressor then itself is adding to the cooling load as it typically draws around 3-7 Hp depending on a/c load, speed, etc. Three strikes right there.

 

I was thinking hot rod without air not street rod when talking mechanical fan....

 

And cost about 30 HP.

 

Which is why I'm going with a clutch fan....

It'll still cost some power, but not as much.

 

I once cut the top couple of inches off a metal trash can , put a hinge on one side to slid it around my fan and attached it with copper wire to make a fan shroud the night before a car show. It worked so well in a pinch I never redid it !!!


Sent from my iPhone using The H.A.M.B. mobile app

 

Make sure it's the thermostatically controlled one. They have the little coiled spring on the radiator side.
https://www.summitracing.com/parts/hda-2747/reviews/

 

Yep..... already bought...