flex fans

[Rory428]

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

I have never tried a Black Magic electric fan, but every electric fan I have tried, failed miserably at keeping the engine temperature down. Also, an OE style electric fan takes a lot of current to operate, if that dyno test was on an engine dyno, the HP used by the alternator load would not be accounted for. A good working fan may eat up some power, but not as much as an overheating, seized up engine does! Also, a heavy fan like a clutch fan, takes power to accelerate that mass, may not show up on a dyno pull, but certainly can on an ET slip. Still, 30 HP seems like an awfully high number lost with a fan, what RPMs were they turning? I would think a single fan belt would have trouble maintaining a good grip dealing with a 30 HP fan, not to mention the water pump and alternator drag on top of that.

[GerryP]

...I would think a single fan belt would have trouble maintaining a good grip dealing with a 30 HP fan, not to mention the water pump and alternator drag on top of that.

This is what makes the data very suspect.  You would need a cog belt if it was eating that much horsepower.  I am also very skeptical of any magazine test.  They have something to sell.  And 50-year-old flex fans ain't what they're selling.

[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.

**************************************************************************************************
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

I have never tried a Black Magic electric fan, but every electric fan I have tried, failed miserably at keeping the engine temperature down. Also, an OE style electric fan takes a lot of current to operate, if that dyno test was on an engine dyno, the HP used by the alternator load would not be accounted for. A good working fan may eat up some power, but not as much as an overheating, seized up engine does! Also, a heavy fan like a clutch fan, takes power to accelerate that mass, may not show up on a dyno pull, but certainly can on an ET slip. Still, 30 HP seems like an awfully high number lost with a fan, what RPMs were they turning? I would think a single fan belt would have trouble maintaining a good grip dealing with a 30 HP fan, not to mention the water pump and alternator drag on top of that.

It was 6,500 rpm or so IIRC,

[cleandan]

I have played around with this quite a bit.
All on street driven vehicles.
I don't like the direct driven flex fans of any sort.
Yes, there are some quality flex fans...and there is some dangerous crapola out there too.

I have found the viscous clutch fans are not as durable as the thermo clutch fans.
I always seem to spin the fans enough to drive the fluid out of them pretty quickly.

The thermo fans give good results but you MUST check them for proper fit, balance and operation and if they don't work correctly take them back under warranty and get a different unit. Aftermarket parts stink these days so it may take a few tries before you get a good unit.

Also check your fan for balance and runout. An out of balance fan is a clutch killer, as well as a water pump bearing and seal sniper.

Keep the whole assembly as close to the water pump hub as you can.
Keep 1/3 - 1/2 of the fan depth inside the fan shroud.
With a properly balanced fan (7 blade staggered works best in most applications) on a short thermo clutch, with a good shroud, you should be able to cool pretty much any engine that is also using a proper radiator.

If you just have to get a flex fan I have found Derale and Flex-a-lite seem to be pretty decently made and durable. Check them for balance and keep an eye on the rivets for tightness, as well as the flex portion of the blade because they do get eroded away with use.

[Falcon67]

If you want to run a flex fan, use one of these in the appropriate diameter - https://www.summitracing.com/parts/flx-1317 

I've run several and the work very well and move a lot of air.  They are also salad shooters, will take a finger off in a blink so handle with care.  A decent size dual 1" core aluminum radiator, 195F t-stat, proper sized and positioned shroud and a 18" unit should cool pretty much anything.

[390owner]

I cant make up my mind. My clutch is still just roaring all the time and my gas mileage is down. I hate to spend 60-70 buck on another clutch and it do the same thing this one is doing. It is the second one from the parts store here in town. The first one did this so they gave me another one same dang thing. I am sure a flex fan would not be as loud as this 7 blade turning at full speed. Sounds like a jet when I take off. I have a  4 speed transmission and half to lug it between gears to keep the roar down Also I looked at some of the stuff you guys posted but do I need a heavy duty or a standard duty if I go with another clutch

[GerryP]

A heavy duty fan clutch is designed to turn a fan with a much steeper blade pitch.  Fan clutches have ratings for how much they drive the fan.  A heavy duty has a high drive ratio to provide the anticipated cooling.  So, if you use a heavy duty clutch with a standard duty fan, it will drive the fan at a much higher ratio than it was designed and even when relaxed, it will still drive the fan with a higher than desired ratio.

If you do not have a fan that matches the clutch, it will not perform as intended.  So, standard fan pitch, standard fan clutch.  Heavy duty fan, heavy duty clutch.

[70tp]

Is it a thermal clutch?   Does it have the spiral spring in the middle front of it?  I had to get three on the Chevy work truck before one would work correctly.  One wouldn’t engage , one stayed engaged the whole time, one would work correctly.  If it doesn’t have the spring, then it’s not a thermal one and may be just the way it behaves.  Sometimes you can “adjust” the spring to make it engage earlier or later. 

[390owner]

I have the spring on the front of mine.It only has one notch for the spring. My fan has a aggressive pitch. My old clutch worked fine until it wore out.

[jayb]

I have never tried a Black Magic electric fan, but every electric fan I have tried, failed miserably at keeping the engine temperature down. Also, an OE style electric fan takes a lot of current to operate, if that dyno test was on an engine dyno, the HP used by the alternator load would not be accounted for. A good working fan may eat up some power, but not as much as an overheating, seized up engine does! Also, a heavy fan like a clutch fan, takes power to accelerate that mass, may not show up on a dyno pull, but certainly can on an ET slip. Still, 30 HP seems like an awfully high number lost with a fan, what RPMs were they turning? I would think a single fan belt would have trouble maintaining a good grip dealing with a 30 HP fan, not to mention the water pump and alternator drag on top of that.

Most of the electric fans out there, including those Black Magic fans, are not up to the cooling job, based on my own experience.  However, the factory electric fans, and also Spal electric fans, cool better than any standard fan or clutch fan of equivalent size.  Usually though, because the electric fans are smaller in diameter, you need two of them to cool properly, rather than just one big fixed blade fan.

My dyno testing does show that a fixed blade fan will eat about 10 HP at 5500 RPM on a typical street engine. 

As far as power consumed by the alternator to run an electric fan, it is negligible.  The calculation is straightforward, because watts and horsepower are a measure of the same thing, just using different measurement units.  1 HP = 750 watts, or 1000 HP = 750 Kilowatts.  If you go to Europe and look at the new car specifications, their power output is measured in kilowatts, not horsepower.  For electric fans, you need to know that watts = voltage X current.  So, if you have two electric fans, each drawing 10 amps at 14V, you have 20X14, or 280 watts.  That's about 4/10s of a horsepower.  If the alternator is only 50% efficient, that means that that alternator is consuming 8/10s of a horsepower to generate the current to run those fans.  That is much, much less than a fixed blade fan will take.

One reason I really like electric fans and electric water pumps is that they run continuously at maximum output, regardless of engine speed.  In the case of a fixed blade fan, it has to be designed to provide enough airflow to cool the engine while the car is stuck in traffic, not moving, on a hot day.  So, it has to be pretty big, and then when the engine is turning at a higher speed it takes a lot of power to turn that fan.  The same thing applies with a water pump; it has to be sized to provide enough flow to cool the engine at idle, and that capacity is wasted at higher engine speeds.  Electric fans and water pumps run at full speed, independently of engine RPM, so they do not contribute to parasitic horsepower losses at higher engine speeds.  Electric water pump plus electric fans will typically save 20 HP at peak RPM on a 400 HP engine.  Electrics are the only way to go, if you ask me...

[64PI]

I agree with Jay. I switched to a Spal electric fan with a shroud and a Meizer electric water pump on my Galaxie. I always had cooling issues with the car being the block is half filled. Several different fans/shrouds/distance to the radiator. As soon as I'd get in traffic the temp would climb. I'm also running 2 Spal electric fans on my daily driven 406 in my truck. No issues at all.

[Falcon67]

Most of the electric fans out there, including those Black Magic fans, are not up to the cooling job, based on my own experience.  However, the factory electric fans, and also Spal electric fans, cool better than any standard fan or clutch fan of equivalent size.  Usually though, because the electric fans are smaller in diameter, you need two of them to cool properly, rather than just one big fixed blade fan.

Here's what I use in my Falcon with everything from the 300 HP 302 to 500HP+ whatever.  Plus a Meziere 30 GPH pump, no cooling issues even at 140F ground temp in the pits.  My trans and the 4600 stall converter heat up quicker than the motor LOL.  31x19 dual 1" core aluminum from Summit, fans off some mid 90s Camaro, LT1 as I recall.  180F t-stat for racing, 195 for everyday street duty with a lower gear and a street type converter.  It's too wide for a Mustang nose, but should fit a Fairlane easy enough.  I opened my radiator shroud a bit.

>One reason I really like electric fans and electric water pumps is that they run continuously at maximum output, regardless of engine speed. 

Note the bleed off openings in the factory shroud to bleed air stacking up in the shroud.  Fixed fans running at a fixed speed tend to turn into a circle of cardboard behind the radiator when running down the road.  Since this is a street/strip car, I have a ton of "relay logic" - key on, pump on always.  Race setup, manual switch fans on/off when key on.  Street - fans on/off automatic by thermostatic probe (removed for racing). Key off, manual switch override of both pump and fans for static cooling. 

EDIT - the other thing here is that the motors are available in any parts store.  IIRC, one made some noise when I first sourced it, $45 replacement made quick work of that.  I've tossed several $$$ 16" and 18' singles in the trash after the motors failed/locked up/whatever. 

[jayb]

...I would think a single fan belt would have trouble maintaining a good grip dealing with a 30 HP fan, not to mention the water pump and alternator drag on top of that.

This is what makes the data very suspect.  You would need a cog belt if it was eating that much horsepower.  I am also very skeptical of any magazine test.  They have something to sell.  And 50-year-old flex fans ain't what they're selling.

I think 30 HP is certainly possible with a good V-belt.  The reason is that I did some experiments back in 2005-6 with the belts running a centrifugal supercharger.  The original supercharger kit that I bought had a 10 rib belt system to drive the supercharger.  This belt would allow the supercharger to deliver up to 12 pounds of boost and 1500 cfm before it would start slipping.  So in the end I switched to a toothed belt, in order to get to 17 pounds of boost.

After switching to the toothed belt, one of the last dyno tests I did was to devise a test to measure how much horsepower it was taking to drive the supercharger.  The results are shown in the dyno section of the main web site, linked below.  At any of the cfm levels shown in the graph, power required to run the supercharger was over 100 HP, so certainly the 10 rib belt was holding that mount of power.  The 10 rib belt does have more area to grip the pulley than a standard V-belt does, but the grooves are much deeper on a normal V-belt, so it's not as much as you might think.  Just looking at one of the 10 rib belts, a good V-belt is at least 30% of that area, and probably more, which means it should hold 30 HP without any trouble.

Of course, magazine tests can be suspect, and a 30 HP difference does seem like a lot for the different fans tested, but I wouldn't dismiss the test based on the amount of power the belt can transfer.  I think that part is totally believable.

http://www.fepower.net/Dyno%20Results/dyno_results_14.html

[Falcon67]

Shoot for about this much air movement and you should be good.

[GerryP]

I think 30 HP is certainly possible with a good V-belt....

And yet on this forum, in the very near past, there is a thread asking for help in stopping V-belt slip and screeching when using a 3G alternator, which at the high end are rated at 130amps.   Certainly there are V-belts being used in industrial applications that are holding well more than 30 horsepower.  But there's no real comparison to those V-belt drives and what you have under your hood.  Two or three belts help a lot but I've used flex fans on single belt systems without slip.  I don't have any data to back that up, but I don't think it matters anyway.  There are, as you point out, considerations other than parasitic loss in the mix.  And that is probably the more relevant data point.