Sbc Fans: Flex, non-clutched, or clutched?

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saryon7

saryon7

10 Year
Joined
May 14, 2011
Threads
32
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313
Location
NorCal
What do you guys run? Do you like the setup? Would you do the same way if you did it again? Why did you pick that setup? Give us your opinions...


I have been kinda leaning towards going with a non-clutched flex fan.

thanks,
john
259-17018.webp
 
I'm using a later-model stock 11-blade nylon fan with clutch on my '96 5.7l and I'm really happy with it. No cooling issues whatsoever.
 
I've been using a 35* 5 blade fan w/no clutch on a gen 1 350sbc. My 1st SBC, back in the mid 80's, was built pretty strong, w/12:1's & such. I had to recore the rad & install this fan to try to keep it cool. The next engine was a 454 & added a small rad in the rear too. Now I run a pretty much a stkish 350 & have no problems w/cooling using a stk rad w/a fan shroud. I dont' care about any loss of HP, I don't want to be hampered w/a marginal cooling system. I've been trail riding w/folks who have had problems w/electric & flex fans, & have seen clutches fail too. One of the most innovative trail repairs was using bondo the to fix the wobbling & slipping clutch fan.
 
I'm running a heavy duty pickup clutch with a seven blade fan. Locks up to about 90% rather than the 60%+ of the passenger car fan. Absolutely no cooling problems in 100+ heat without a shroud on my carbureted 350.
 
Flex fans seem to be frowned apon.

I've been running a semirigid flex fan since before my conversion in 1996. It work well but gets loud as RPMs increase.

Figured I'd switch to a Taurus electric fan... But most seem to recommend clutch or mechanical these days.

I'm undecided... Sticking with what works for now.

Initially, I found the automatic engined pullies didn't spin the pump fast enough while crawling on the trail. A smaller pulley solved that issue. The climate is fairly mild here though.
 
I have had good luck with a fixed blade fan, steep pitch, like from a truck or caddy, 7 blades and a clutch from a truck, they have more-and larger fins. Also run a well made fan shroud.
No clutch can kill your mileage and can be noisy.
When in doubt, try to mimic what Chevy did with there heavy duty trucks and high horse power engines. As a rule they had no over heating problems and were operated by the general public with no mechanical know how.
 
pb4ugo said:
I've been using a 35* 5 blade fan w/no clutch on a gen 1 350sbc. Now I run a pretty much a stkish 350 & have no problems w/cooling using a stk rad w/a fan shroud. I dont' care about any loss of HP, I don't want to be hampered w/a marginal cooling system.

riderjgs said:
I'm running a heavy duty pickup clutch with a seven blade fan. Locks up to about 90% rather than the 60%+ of the passenger car fan. Absolutely no cooling problems in 100+ heat without a shroud on my carbureted 350.
Click to expand...

These sound like a good way to go. I will be using the stock radiator too. Do you have a year and model of vehicle for the fans and clutches you guys are running so I can tell the parts guy?

I would love to see some pictures of these setups too.

How come no one runs flex fans instead of the hydraulic fan clutches?

thanks for all the replies. Anyone else wanna chime in? I would love to hear it.

thanks,
john
Click to expand...
 
pb4ugo said:
How come no one runs flex fans instead of the hydraulic fan clutches?
Click to expand...

Same reasons that not a single auto mfg uses them. They are inferior, dangerous and noisy.

I wouldn't run a fan without a clutch.

If I had some clearance issue, I would run a Taurus or Volvo fan, but not without a variable speed controller.
 
Fast Eddy said:
Same reasons that not a single auto mfg uses them. They are inferior, dangerous and noisy.

I wouldn't run a fan without a clutch.

If I had some clearance issue, I would run a Taurus or Volvo fan, but not without a variable speed controller.
Click to expand...

Ditto. stock HD fan with clutch.
I watched a guy suck his flex fan into his radiator on a water crossing. A clutch fan
will stop turning. A fixed fan will turn like an outboard prop in water. A fixed flex fan will do just that...flex ...right into your radiator core
 
Running belt driven fan as well, SBC. Flex fans are loud and as stated above, water crossing or mudhole, it'll find its way into the radiator. My current setup runs at temps anywhere from 180-190. Drove it yesterday with outside temp around 90 and highest I saw it go was 195.
 
To determine which fan/clutch setup to use go to a Pic a Part junk yard. Bring a tape measure, paper and pencil. Search for trucks with SBC. The heavy duty kind are better. Note the mounting bolt size. Look for the ones that match your setup. Measure the fan size, the biggest that will go in your truck. Note the clutch that is used. The heavy duty clutches are larger than those used on cars and have more fins on them. Sometimes you can find a clutch that is in good shape and pull that one along with the fan. Write down the vehicle information from the truck that supplied the parts.
After looking around for awhile you will become an expert on all things cooling.
 
I'm running the world's oldest, crustiest flex fan, and it keeps my truck cool, even without a shroud. (I know, totally :hillbilly:)

The fan is loud at speeds. Then again, the truck is loud at speed regardless so I don't really consider this an issue. Just sounds like I'm driving a tank. :D I also like that I'll never have to worry about the fan clutch wearing out.

A couple things to consider:

1. Flex fans sap more power than clutch fans due to their added resistance at higher RPMs. Again, not a big deal to me since I'm not building a drag car, but they might cost you 5 horsepower and some fuel economy.

2. Consider the engine location in your truck. Clutch fans take up more space than a flex fan. If your engine is mounted really far forward, like mine is, there may not be room for a clutch.
FJ40 No cowl.webp
 
RWB, Flex fans are similar to the 1st pic in this thread. They don't pull air @ high RPM's, so there's minimal loss of HP. They flatten out. The fan in your pic appears to be a std fan, no or minimal flex. It will rob a little HP.
 
Stock GM clutch fan. It worked in the OEM vehicle, and works just like it's supposed to in my not-so-OEM FJ40
 
pb4ugo said:
RWB, Flex fans are similar to the 1st pic in this thread. They don't pull air @ high RPM's, so there's minimal loss of HP. They flatten out. The fan in your pic appears to be a std fan, no or minimal flex. It will rob a little HP.
Click to expand...

Good to know! Everyone I've talked to has always called it a flex fan, so I guess I've just been misinformed! Either way - it's noisy and it works Ok for me!
 
My setup- sbc 327- AFI/
Running a stock chevy fan clutch, with fan shroud.

No issues cooling even in Moab in July.

Runs cool!
 
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