flex fans

[390owner]

Does anyone run a flex fan on their 390? I am thinking about changing to flex from a clutch fan. The only time my engine gets a little warm is sitting in traffic when it is real hot outside. That is where a flex fan would work for me. My clutch fan stays engaged all the time. It is new and the second one. I bought a standard duty one off line and never locks in when hot or cold. What is a good flex fan?

[cammerfe]

Years ago, I changed the clutch fan on my '75 Mark IV/460 for a heavy duty flex fan with a steel hub and stainless blades. The clutch had dried out and the engine was running warm in traffic.

The flex fan was a name brand but I'm not sure which one---this happened about '78 or so. There  was a very decided curl to the flex blades and gunning the engine would cause the blades to flatten out a bit, but you'd have to have seen 6000 or more to really get them flat. And the air the fan moved made a LOT of 'whoosh' noise. I kept it because it cooled very nicely and the inside of the car was insulated enough that the noise didn't intrude significantly. Ya pays y'ur money an' takes y'ur choice, I guess.

KS

[Rory428]

In the past, I have been very happy with Haydens 7 bladed 18" stainless steel blade flex fans. I ran one of my old 70 428 CJ Mach 1, it always maintained a good temperature, and I recently installed the same model fan on my 59s 428. I have also had good cooling with a 5 bladed Ford PU truck fan, kinda looks like a flex fan, but the blades ,which are riveted to the center, are so thick, that they can not flex. Cooled well, but quite noisy.

[390owner]

That is my problem now, the clutch is engaged all the time and it roars like a big truck.

[allrightmike]

A friend of mine had a Comet with a 302 engine that had a very elusive vibration that would come and go. Installed a constant velocity driveshaft U-joint, changed the torque convertor adjusted pinion angle, on and on it went. Yup, it was the flex fan!

[machoneman]

Think if you bought a quality piece like a Hayden clutch fan, non-thermal, you'd be o.k.  Find the right one here:

https://www.summitracing.com/search/make/ford?keyword=hayden%20cliutch%20fan%2C&ar=1&kr=hayden%20cliutch%20fan%2C%20ford

[390owner]

Ok I will check it out thanks.

[fairlaniac]

Well since we''re on flex fans I must confess about one of my stupid moves over the years. In the 70's a young hot rodder could go to a local speed shop (American Speed York, PA) and a cheap "hot rod" item was a flex fan. It would unleash gobs of horsepower on a stock '71 F100. So I bought one and enjoyed the HP gains for a few years. So 1982 comes along and my grandfather who was a Ford Dealer in Ephrata, PA called and told me Ford was putting out a Mustang GT 302 (5.0) and 4 speed only. Within a month I had one. I drove it at first without mods to maintain the warranty. 12,000 miles didn't last long and within 6 months the warranty was up and time to mod. Now I was all but broke with the new car ($9977 list). So I visited American Speed again and bought a blue anodized flex fan. I felt like a bad ass. I think it was by Spectre? I went home, installed the fan, and flipped my air cleaner lid for more HP gains. FYI - the Mustang had a nice dual snorkel, fresh air cleaner of it's own. It was time for my maiden  high HP voyage. I recall heading down Rt. 116 in Spring Grove, PA and the hammer was down. The air was sucking through the air cleaner and all of a sudden I heard a helicopter. It really sounded like a helicopter. I got out of the gas and looked around, nothing, the helicopter must have passed? I did another hit and I heard the helicopter again. No helicopter in the air, must be something with my fan? I also notice my temp gauge climbing. I pull over, pop the hood and stare at the engine for a while. I restarted it and watched some more. Then I watched the serpentine belts for a while and there it was. My quick lesson into the reverse rotation of the water pump on serpentine belted 5.0's. Went home, changed the fan and hid the box and fan under my bed. Didn't want anyone to find out what a goof I was :-)

[GerryP]

I would like to say we've all made that mistake, Doug.  But, no, we haven't.

[machoneman]

At least it wasn't a fatal for your engine goof. Easy to do the wrong water pump too. Ford and aftermarket pump makers should have put an "R" into the castings for Reverse rotation. 

Liked the helicopter sound many others here have heard on occasion. Had someone bring me their car and after a drive, popped the hood to find a locked up old clutch fan. At speed, it did sound like a chopper was tailing me!

Another time, a car was overheating and a head-scratcher as to why. Had the owner fire it up and while watching the engine as the throttle was cracked, I noted something odd. The fan blade was wobbling far more than it should. On shutdown, I found I could spin that clutch fan like a top and it spun freely....forever. All the fluid had leaked out!

Still, I'm big fan (ha!) of clutch fans as they work well in muscle cars of all makes. Too often, the flex fans are REALLY noisy at highway speeds or when making a high rpm run. The aluminum blades at least were better in later years as many a hood, radiator, etc. were pierced by blown-up fiberglass finned flex fans. I guess they flexed a tad too much and shed the blades in protest!

[Gaugster]

How the aftermarket fan aligns with the shroud has to have a big effect also. This assumes you are running with a shroud. So the spacer/clutch depth needed to be considered. (As well as rotating direction. )

As an aside I just put back a factor 7 blade fan and Thermo clutch. It replaced an autoparts store plastic fan. Not a flex fan in the true sense. Cars not been out on a hot day yet but I could immediately tell the engine had less vibrations. The old fan was just a low quality item.

[frnkeore]

Another consideration could be a solenoid operated fan. I know they use them on trucks but, I don't know if there are car applications. A manual override switch would be useful for a drag racer.

[TomP]

I had great luck using the stock six or seven blade fans that come off 351M pickups and others. I've used them on lots of cars.

[wowens]

Think if you bought a quality piece like a Hayden clutch fan, non-thermal, you'd be o.k.  Find the right one here:

https://www.summitracing.com/search/make/ford?keyword=hayden%20cliutch%20fan%2C&ar=1&kr=hayden%20cliutch%20fan%2C%20ford

Why non thermal ?

[machoneman]

Per an old Car Craft dyno test (may try and call it up again) it used the least HP (lesser than a HD thermal).

On Edit: Could not find the article as it's now 20 years old! Here's a cut and paste. BTW, the two thermal choices (I fogot how close they were in the test) are only 2 hp apart so as long as one gets a non-heavy duty clutch, you're good to go. I should mention too if your inclined, the electric fans are the absolute best for the least HP loss.

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Funny thing, right after I read this question, I happened to pick up an old Car Craft mag from May 2000. They did a dyno test to see what the loss was on a 496 hp SBC. Take it for what it's worth but here are their results:

Alternator, no fan - 496 hp
One piece Plastic 6 blade flex fan - 460 hp
Low profile 6 blade flex fan - 466 hp
High performance 6 blade flex fan - 476 hp
OE replacement 6 blade rigid fan - 449 hp
Nonthermal 6 blade clutch fan - 485 hp
Thermal 6 blade clutch fan - 487 hp
Heavy duty 6 blade thermal clutch fan - 476 hp
Used stock 4 blade rigid fan - 473 hp
Black Magic electric fan - 494 hp