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Holes and flappers in schroud? Good Idea?

10K views 12 replies 10 participants last post by  malc 
#1 ·
On my 355 SBC I have a Champion aluminum Rad with a puller fan. At idle and in town temps are at about 195. At highway speeds 65 or so I see them getting about 200. I know thats not bad but I just put my vintage air back in and the temps are 80 now but will be 100 soon. A buddy told me I need to cut holes in the shroud and install flappers. Will this help? I have room for 4 two inch holes. Any input will be appreciated. Thanks in advance.
 
#3 ·
I agree with RWENUTS. Relatively cool in town and overheating on the highway is an airflow problem. Not enough air through the radiator. Possibly not enough exits for freeway hot air generated, stagnated engine compartment. Re-direct the air, beginning with a dam, then opening enough area at the firewall/fenderline/hoodline to evacuate the engine bay at speed.

Bill Thomas, when fiddling with Corvairs, found that a piece of sheet metal removed from the underside of the motor to help reduce weight had actually been the only reason the motor cooled. With that piece removed, air coming under the car at speed pushed up onto the air that was being pushed out by the motor's cooling fan, stagnating the air and not moving enough air through the fins to cool the motor, resulting in an overheating condition. Replacing the sheet metal pan under the blower fan restored airflow out of the motor, resulting in normal operating temps once again.

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#4 ·
I have the same problem, my car runs hot at speed. I have my car down for a major overhaul right now. When I get around to re-assembly I am going to make a new fan shroud with thin rubber flaps to let air pass through at speed. I read that the fan can actually act as a restriction to airflow at speed so I purchased the F5 fan controller from Painless wiring. It allows you to automatically shut off the fan at an adjustable speed (also need to buy the speed sensor ). It makes sense to me that if the fan is large and covering a major portion of the radiator and the shroud is covering the rest it could pose quite a restriction at speed. I also like the idea of air dams under the car to help pull hot air out of the engine compartment. I'm sure it will take several changes to fix this problem, I am also getting a Stewart high flow water pump and a larger radiator.

 
#9 ·
If your shroud completely covers the rad and your using an electric fan the flaps will make a huge difference on the highway, I wouldn't limit them to a couple holes...I would fill the shroud with as many odd shaped holes with flaps as I could fit.

Here is a well done off the shelf system from Derale, easy to copy with some rubber and pop rivets...probably could easily add more to their setup too.

 
#10 ·
I thought I'd let everyone know what I did about the flappers on the radiator. I did two flaps about the size of a business card. Used a soft pliable piece that is used on thresholds on doors. I tested the system the day before, 78 outside and drove about 11 miles at 3100 rpms thats about 65mph. Temp was at 205 constantly. Did the flappers and ran the same test with identical temps outside. Temp never went over 195. I know that 205 wasnt high but when it gets 95 to 100 and I have the AC on it will make a difference. Thought Id let everyone know, thanks for all the advice.
 
#13 ·
I built a new full shroud with two fans and added holes covered with a rubber flap.


The flap was quite flexible, enough to "flap" but stiff enough to stay in place while stationary.
Did´nt seem to work, same results, engine temp, with or without.
At the moment I´m without the flap deciding what to do.
 
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