Have an 18" fan on the small block. Fabing shroud for same. Thinking of going to 17" fan .would cooling be affected with smaller fan? Trucke
If you are building a shroud and can make it any size, I don’t think diameter would be as important as pitch of the fan blades.
You never know what result you will get until you do it and test it. It could be the same, could work better, or could work worse..........no one can tell you positively what result you will get. Not trying to be a smarta**, just telling you the truth. Its really one of those things where a certain change is expected to produce a certain result.......but the actual result sometimes doesn't do the expected. All you can really do is make it and see if it works ok.
While the size of the fan is important, what matters more is the shroud vs. fan relationship. The leading edge of the fan should be just inside the shroud opening with no more than about 1" clearance between the outside diameter of the fan and the inside diameter of the opening. That clearance will allow for motor movement.
I'm with @Bandit Billy on this one, all the cars I built I alway put the biggest fan I could. Of course I always ran Pontiacs and I liked them running in the 170-180° range. Seemed I always ran the factory A/C equipped clutch fan with a heavy duty Napa fan clutch. Never had one that ran too "cold" doing this. Although most of my Pontiacs ran 10.5 and higher compression too... ...
You already have over heating problems, in a previous post. Now you want to go to a smaller fan, with fewer blades ? Great idea.
I,m going to use the 18" if possible. Only can go 19" on the shroud hole unless I stretch it out somehow at the sides. Trucke
My Buick only has a 16" fan, no shroud. Does not overheat. What it does have is enough radiator that is clean. AND THAT IS IN OUR 100+ Texas weather. Ben
Referencing what I said earlier about "no one can tell you what result you will get"............ the things I would try to insure are that your shroud has a good fit, maybe with some form of glue on seal around its edges. What happens with some fan shrouds is that the gap at those edges allows air to be drawn thru there instead of thru the radiator, and people don't realize it's happening. I would also try to make sure there is some room between the shroud and the radiator so that air can be drawn thru the fins that are not directly in line with the fan. There has to be room for air to pass thru the fins and then travel down to the fans flow path. One test I would suggest before mounting your shroud is to get on a highway and drive at several speeds and note what temperature your engine runs when there is no shroud or fan. You may have to stop somewhere and let it cool, but you will at least know whether it cools or not at highway speeds using just external airflow....which is pretty much how most systems are supposed to function.....that's why the old mechanical OEM fans had fan clutches. Find out what you have and then you can see how your upgrade affects that part of your driving.........and if it now cools when idling or city traffic. The idea is that if your system is unable to cool at highway speeds, then it is probably not going to cool in city traffic even with a fan.
This helped with my cooling problem on long wait intersections or stop/go traffic. A smaller water pump pulley did more. 16” 6 blade
Pulled the electric off my coupe when I went back to carb. Used a Zips pump adaptor. 16 inch fan and cooling components fiberglass shroud. Drove today 103 degrees outside. Ac on 165-185. 185 at an extra long light. Cooled right back down.
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