Most likely the 6 blade, you need most air flow from a fan at lower RPMs when the vehicle is not moving at speed. But flex fans can cause a issues situation at higher RPMs when they could come apart. Should be able to find a 6 blade metal fan and keep things better than equal
I use this steel blade fan on all my hot rods, Nothing runs hot even in bumper to bumper traffic. HRP
^^^^ I bought one of those from Summit by mistake. It’s a nice fan but it seems a little heavy compared to the ones I usually use. Right after I got it, I found the one I wanted at the swap meet for $10. I packed up the new one to return it but I had second thoughts, with other projects underway I may have a use for it. Your comment just helped me make up my mind to keep it and try it. I’ve never done any kind of tests but it seems like good quality stainless flex fans move more air at low speeds than the common factory four blade and that’s good for low speed driving and sitting in traffic. I’ve never had one loosen or come apart but then I don’t take them to extreme RPMs either. This is the one I got from the swap meet. They work well but don’t look right on a HAMB era car.
'61 or so from a GM big car, 17" clutch fan, made an adapter to use with out clutch. Aluminum. Quiet.
From above - This one draws a LOT of air, but the faster it spins, the noisier it gets. Had one on one of my cars for almost 100,000 miles. Kept my ol Stude engine cool, even in 110° SoCal summer days, waiting in the In-n-Out burger line for lunch ! Mike
Looking through old magazines I was surprised to see a lot of hot rods running without a fan. I lived in LA most of my life and I can’t imagine driving around in traffic or sitting at stop lights without a fan. On the other hand, my ‘28 coupe has a small electric fan but runs at 180 on normal 70-80 degree days without it as long as I don’t sit too long. On most runs I don’t have to turn on the electric fan, only when idling for long periods or on 90+ days.
Factory clutch fan as seb fontana mentioned. Group thoughts on shrouds? Every hot rod I owned had one and I think it helped to keep the temps down
I have had a few flex fans come apart on me. So have my friends. I have fixed about 7 holes in glass and steel hoods. All our engines regularly saw 6500 plus rpms. The black Checker Cab fans are great for low rpm usage (under 4500 rpm) and sitting in traffic. But you can’t beat a 7 blade clutch fan. We never lost one of those and great in traffic!
A decent 6 blade the same size is going to pull more air than a 4 blade, that is a given. A not at all decent six blade like the tapered blade fan in these photos won't pull enough air to write home about. I had that one on my 48 for years and it was almost as bad as no fan.
Did you know, an odd number blade fan pulls more air than an even numbered one? Even numbered fans create a vortex in front of them, that an odd number fan chops up the air being an odd shape. I read that somewhere, I have used stock five blade fans in all my builds.
Some OEM fans have the blades in an irregular pattern, too....they are not spaced equally. I doubt aftermarket fans have anywhere near as much design effort and testing as OEM stuff. as usual.
This is an interesting thread. My flatty is running at about 165 to 170 degrees in all kinds of traffic. I had a Ford aluminum 6 bladed flathead fan on there and it was noisy as hell! Sounded like a jet getting ready for take off! To cut down on that noise I went to a 4 bladed fan fully expecting to see a rise in the running temp of the flatty. Interesting thing was it seemed to make no difference. The engine still runs at about the same temps but is significantly quieter.
Odd number of blades and unequal spacing of fan blades might be an interesting study. I’m sure that the auto manufacturers put significant effort into making the fans efficient and as quiet as they could but building hot rods introduces a factor that they don’t have to consider, appearance. Clutch fans look ok on a muscle car but look out-of-place or just plain silly on a ‘30s hoodless car. Same with later model odd bladed fans and most shrouds. Unless, of course, you don’t care how it looks as long as it works.
Fascinating, I recall the 5 blade Ford truck fans that had a distinctive sound and wondered if it was due to the odd number of blades. My engine builder recommended the 7 blade Mopar fan as the best. Although he is heavily Dodge biased. To run them on my Olds, they would require modification (bolt hole re-locating) I will try this,and if better cooling results are obtained I will advise.
For what it's worth, the questions about fans has been a ongoing debate for the past 19 years that I gave been a member, from my point of view I have used original, electric & aftermarket aluminum fans. I have experienced catastrophic failure with a aftermarket aluminum fan that severely damaged a expensive radiator and to be honest I had a electric fan because the aluminum fan just couldn't do the job alone. One thing is for sure, since I started using the 6 blade steel fan more than 20 years ago I haven't experienced that sick feeling of sitting in bumper to bumper and watching the temperature gauge peg out, seeing steam and smelling antifreeze. I'm a firm believer in using a quality copper/brass radiator & a steel bladed fan, that's what works for me. Bottom line, use what works best for you . HRP
Personally, I wouldn't use a flex fan for reasons stated. If you don't care about appearance, I would use a "puller" electric fan/w adequate cfm rating for your application. Either thermostatically controlled or on/off switch will allow you to turn it off when it's not needed. Whether mechanical/electric, use a shroud that fits to ensure that the air is being drawn through the radiator.
My avatar had a flex fan with no shroud when I got it. Worked OK, but it would tend to get hotter in slow traffic or parades, but never to the point of actually overheating. My main beef was it was very noisy; sounded like a pusher school bus when pulling away from a stop. Plus that nagging thought that it may fail as these are prone to do. Electric fans are more trouble than they're worth IMO so were never an option. I went to a 5-blade thermostatic clutch-type fan with a shroud. The fan noise was pretty much gone, engine temps have stabilized and I even picked up a small improvement in fuel economy. One downside is these have a minimum length of about 3" from the pulley to the face of the clutch (you can get longer versions) so can be very tough to package in close quarters so may not always fit. The other downside is fan sizes are limited, I had to shorten the blades about 5/8" for fit. As long as you carefully remove exactly the same amount from each blade you'll have no issues with balance. I cut a 17" fan down to 15.75". The shroud was a huge PITA to build/mount, but that had to do with the 'unique' way the original builder mounted my radiator, it wouldn't be nearly as much of a problem with a 'normal' mount. One other nice thing about clutch fans is they limit fan speed. Because the fan isn't direct-coupled to the water pump, max fan RPM is about 4000 RPM regardless of engine RPM so exploded fans are very unlikely.
I have used these 15" steel six blade fans on several dirt cars. This one is for my roadster project. It's a heavy duty ridgid fan rated for 8,000 fan RPM. This one came from Speedway but I'm not sure it's their product. It's a dead ringer of the 17" Derale fan Summit sells. Have never had an issue in hard use. Since I blew apart a flex fan that was on the 301 in my '55 Chevy many years ago I just don't use them.
If a 4 blade fan works, use it. This one works just fine for me, the engine never overheats no matter the ambient temps or traffic conditions. Slow moving, or not moving at all, makes no difference, engine temp remains right around 180. No shroud needed. But it's a different story in my 47, with this 7 blade fan (and Walker copper/brass radiator) it will warm up in slow moving traffic. It needs some movement, which I think may have more to do with coolant circulation than with air flow.
Most over looked thing about fans,on cars=Any fan,should have a good fitting fan "Shroud ". I've custom made a good number of them,and been lazy at times ,not replacing shroud ,when in a rush to get going. Then pay for the lazy mistake,when rush hour slows me down.
Is the fan centered on the radiator? if the fan isn't centered could you benefit by using a zips riser?or could you use a larger fan? The zips riser will move the water pump up 5 inches. HRP
My last %0s Ford 8BA had an electric & stock fan on it & ran hot. I removed the electric, installed the correct stats & that flatty ran at 180-190 even on 90 degree days. It isn't always the fan ....
Blues4U I wonder if the difference between your two cars is an enclosed engine compartment versus an open one? Also, if a car came from the mfgr with a shroud then I would put one back on the car. If it didn't originally and your running a pretty much stock motor I don't see the need personally if your cooling system is stock and up to snuff as well. If the motor is modified then you do what you need to to get it to run at the best operating range you can.
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