Hello Guys,
I am putting a shroud on my new aluminum radiator,its a universal shroud from summit to fit the radiator ,but I have to cut the hole for the fan.By the time I get the fan hole fitted ,there is only going to be 1 to 1 1/2"to the sides left on the shroud,ant the fan is gonna be above and below the shroud by several inches.So, is it really worth all the fabrication to put on a shroud that will only cover maybe 15% of the radiator.The fan will be about 1 " from the radiator ,and like I am saying,it covers 85% of the radiator.Any opinions???

Thanks Craig

I have an opinion, and its predictably not shared by many I would guess. A shrouds main purpose is to provide a venturi for a rotary fan to improve its pumping effiency. The closer the venturi tube, the better, of course in a car in can never touch. The next purpose is to channel the inlet air thru the item being cooled, the radiator. Many think that the entire amount of air the fan is moving must be moved thru the entire radiator. This is where I disagree. I believe only enough air needs to be drawn thru the radiator to provide enough engine cooling under the worst conditions, ie high ambient temps, no car movement, without too much temp rise before car is likely to move, that's a time factor, and every car/situation is different of course. The problem I see with over shrouding, which I think is the point of your question, is at speeds over say 60mph?, your fan becomes pretty much an obstruction to air flow and is almost useless and a hindrance. If the restricted air can find a new less restrictive path around the fan, but still thru the radiator, you have a good compromise solution. Others may differ.



https://board.moparts.org/ubbthreads/show...e=1#Post7973457

Pic #43 shows a simplistic workable solution

JCC ,I should say that this is the second radiator,as the first was destroyed by the fan digging into it in a "panic" stop situation,where I stopped very hard at a yellow/red light and the engine rocked forward in the mounts and damaged the core.I had the fan 1/2 inch from the radiator,and no shroud.This setup cooled adequately,except in stop and go traffic the temps would rise pretty quick (200- 210 degrees) until I got moving again,then never above 185 .Down the road it was good.This is in my 78 dually,tow rig,440 d300.I was thinking the shroud would help that low speed issue,especially since I am taking out the 1/2 inch spacer to give the radiator some more clearance to the fan.I have changed the mounts,so that should not be a problem again,but wondering if this shroud will restrict airflow going down the road.I am thinking withso little area behind the shroud it probably wont hurt.

The diameter of the opening is supposed to be 10% of the diameter of the fan.

->18" fan...1.8" plus 18" equals a 19.8"hole. Or .9" gap around the fan.

The fan blades should be half in and half out.

That is from an Engineer that worked for a big international radiator manufacturer. Sirca? Circa?

I definitely have those criteria met. I just wonder if there is enuff shroud left to make much difference?

For another source of info, might want to read this link, especially paragraphs 4 & 5 on "Airflow".

http://www.hotrod.com/techarticles/engine/cooling_system_tech/