As the title states.. Comparing different fans with each other. Mods may move this to approriate section, "other" felt good for now.

Having too much time at hands currently, and need to spend it somehow. When i stared my engine yesterday, it missed something.. It was the look of clutch fan on it. Ive personally used electric fans, converted from mechanicals. I never Felt ANY power difference between those two, it was always just for the sake of doing something, or like in this case, the lazyness to hunt for correct parts.
Idea to write something about the subject, trying to stay on proven facts, raised when out of curiosity, i made a mistake and googled.. Id say, ive never read as much bullshit and almost religious aspects reaching tell-tale about any other subject relating to our belowed car hobby.

Lets start on electrical fan

As the name implies, its driven electrically. Its free of engine speed, dont need to be turned when not needed, so not taking up any power. Can be driven automatically or manually, takes less space than clutch-fans when space is Premium. Yet many people have cooling problems, which by quick googling, is always blamed to something else than their new electric fans. Problem lies on how manufacturers rate their fans. And price. What will sell most? Combination of smallest price with highest advertised CFM.

For example i choose 12 inch fan- since typical radiator can fit two of them. First lets look Derales ( which seems to have good reputation) universal fan. Its rated 1450cfm, and having amperage draw of 21A. Its typical "universal" fan in a way that theres actually no more info about it.
Lets compare it to one from SPAL ( of which i have two), also 12 inch, rated for 1650cfm and amperage draw of 20A. SPAL is used for comparing as manufacturer, due to it being one of the few providing whole "fan table".
First. Published CFM numbers which are used to sell, are measured with zero static pressure. Typical installation, with fan(s) behind radiator faces static pressure from the radiator core itself. From few sources i found, typical static pressure radiator shows is between 7 to 15 mmH2O. Lets say 2-core is 7 mmH20 and 4-core radiator is 15 mmH2O. And typical 3-core lies between, therefore presenting static pressure of 11 mmH2O.
Now, lets see where 10 mmH2O static pressure puts us at "fan-table" on SPAL unit ( due to them listing every 5 mmH2O- all tests are done with an voltage of 13.0V). Its 1251cfm anymore- with an amperage draw of 16A. What we first notice from this, is that our closer-to-real-world cfm number just dropped by 399cfm's- or 24.2%! With dual fans, that means we just went from 3300cfm down to 2502cfm. Next you notice the amperage draw- 16A. But wasnt they supposed to be 20A? The amperage draw they publish is merely how powerful their motor is- in case of SPAL, as they are tested at 13 volts, so its 13 x 20 = 260W motor each. It shouldnt be pulling the max amp its rated until undersized. Looking the same chart, lets say you have a dented or clogged radiator, and without going to extremes, choose static pressure of 15 mmH20. Its down to 944cfm anymore from rated 1650cfm, with an amperage draw of 15.9A. And remember many of us have AC-condenser in front of radiator, therefore adding to static pressure aswell. One thing here to note also, is that SPAL Automotive is on market to build electric fans for OEM's and aftermarket, been since 1970 on that route. They test their products, invent, and publish full data-charts. So, in best case, manufacturer just re-labeling universal fans, might reach the same performance level as SPAL or comparable, but in most cases, they fall in their face way harder than these, and notice how much rated CFM differs from real-world-situation even with quality manufacturer like SPAL.

Theres a link to SPAL data-chart from the fan i used as example. There you can find all of their data-charts aswell.

https://www.spalautomotive.it/axial-...0_ll-79s/31299

Lets talk about power. Using amperage draw of 16A, and 13 volts ( due to having accurate numbers published by SPAL), they are using 208W each, so 416W total. Thats approx .55 horsepower. Turning alternator with higher load also needs some horsepower, also converting mechanical motion to magnetic energy, then from AC to DC, and then to turn fans also loses some energy, but usual tests, which seem somewhat trustworthy, in conclusion shows that electric fans take few horsepower to turn from engine.

In short. Requires the least power to run, can be used only at demand. You need good ones to actually pull any air through radiator in real-world situation, plus added complexity to run them, plus strain to alternator.
These broke aswell, actually these have far more parts to fail than mechanical fan. Wiring, relays, sensor, fans themselves.. I mention this since googling a bit, one of the favourite reasoning to convert for electric fans, seemed to be that clutch fans can broke, and metal blades can fracture and fly off.

Fixed fans - As the name says, they are fixed to whatever they are attached to. Water pump. They turn constantly. Problem lies on the fact, that as the rpms raise, so does the fans despite of the need of cooling. Also while driving higher speeds, when engines usually dont need additional cooling from fan, it Still turns. So its adding drag/ robbing horsepower constantly. Pros for sure are that its the most dependable one, almost nothing to broke. Most serious BS i managed to google, was one guy seriously stating that fixed fan actually gives power at higher speeds, when ram-air ( lol) through radiator actually start to turn the fan and via v-belt actually adds to engine power……..

Flex fans also belong to these, as they turn at water pump speed. They are designed so that with higher RPM's the blades flexes to be straight and reduce the drag they present. Problem in that lies on fact, that your engine may need cooling at higher rpms as well. Like climbing up steep hill with a load, low gear, slow speed, so not much "wind resistance" to cool the radiator. For flex-fan to be always effective, it needs to be way overcalculated, therefore taking unnecessary power to turn.
There is also the fact, that sooner or later the blades will break, since flexing metal fractures it.
One thing to consider; if flex fan is so superior, why didnt the bean-counters use these instead of the more complex and costly thermal-clutch fans, especially when their job is to provide maximum profit to owners of Company.
Aftermarket seems to like these; they do their job, and are cheapest option out there. But all in all, as sayed, they do their job aswell. These take the most average power to use.

Thermally controlled clutch fans - Thats what the OEM's run for decades. And their use continues to this day, even if in minority. Nowadays there are emissions, space limitations, sideways mounted engines etc to ponder about. Not so much in our cars. Ive been always fascinated about mechanical devices, and these are ingenious.
They feature simple operating principle, where they start to lock-up from heat coming from radiator, and loosen when heat decreases. So, when its needed, they provide maximun cooling, and when not needed, they free up the energy up to a point, since they never fully free-wheel. At cold start-ups, these are engaged for short time until working properly. So in short, they work by demand.
From Hayden's site, which seems to be currently the premier manufacturer of these, they have listed 3 different types of ( thermally controlled) fans; standard duty, heavy-duty, and severe duty. Really loosely going like standard car, hd-cooled/ AC car, and towing trucks etc.

Lets took their 2747, which many seems to use on their muscle cars by googling, and are happy about it. Its rated as their Heavy-duty clutch fan.
As they list it:

• Turns the fan 80-90% of the shaft speed when engaged for increased cooling.
• Turns the fan 20-30% of the shaft speed when disengaged.

So, it provides almost maximum CFM provided by the actual fan-blade design when needed and when not needed, frees up alot of energy what is used when in demand.

By quick googling, most of the problems when blaming clutch-fans to hell, were related to people not checking does they actually work, since these can and will break like anything else, either free-wheeling constantly, or being engaged constantly. And plain simply having wrong clutch to their need, since there are different clutches manufactured for different combinations for a reason. Theres no one-size-fits-all clutch.

In conclusion, given you select right clutch, these are as simple as fixed fan, just bolt on and go, plus they are work at demand therefore not needing as much energy to turn when not needed as fixed fan. Just the clutch seems to cost more than flex-fan, and they can break. Uses second-least power after electric fans. Also needs the actual fan around it.
And by the nature of it never really free-wheeling, when RPM's raise, so does the energy needed to turn them aswell. But in typical RPM range its neglible.

Non-Thermally controlled fan clutches - Per Hayden, having constant slip, 30-60%. Cant really figure out nothing good about these. They are just cheap? You might aswell use fixed fan then. When you count the slippage, and have correct fan regarding size, pitch, blade count to cool the car adequately on every situation, you might have aswell gone to correctly sized fixed fan. Please comment if youre not in agreement.

 

So there is now listed our options for our belowed cars. Tried to stay on facts, and point out one common bogus on advertising electric fans. Had to make another post after reaching word-limit per post.
So if we purely focus on power, it goes electric- clutch- fixed. I found some for sure inflated test, where there were up to 46hp difference between electrical and flex-fan. Everything sized properly for engines cooling needs, and engine being on good working order, im just simply not buying this. For clutch fan, most tests listed approx. 10hp down from electrical fans. But after all, these are all dyno-tests, paid by someone, not real-world results.
General public consensus seemed to be, that after swapping the clutch fan to anything- be it flex fan, or electric fan, they FELT the power added, and 1/4 mile went tenths faster ( mentioning as side-note that they had done some other minor stuff in side, like adjusting timing…). Funny thing i have never felt any difference.
Of course ive never had a change to test high-powered car with electrical fans and clutch-fan side-to-side. But few really reputable builders who id trust, when speaking of street cars, have stated that theyve seen at most a change of hundreths on time slip. When everything is working and properly sized.

Big part of the cooling is also shrouds, lips, correctly sized radiator and such. Block 50% of radiator by installing one 16" fan at middle of it enclosing rest with aluminium plate, and problems are waiting. Or just lose some of the original front lips and problems will arise. Gen1 3A VW Passat got cooling problems always when the lower front-lip got driven to stone. Usually factories did the best job designing their cooling system, including all the shrouds, lips etc. Altering them is shoot in the dark.
One thing that inquires my mind, is when for example our cars were build, did factories account for more or less constantly turning fans moving the air on the engine bay, thus decreasing under hood temps? Anyone have any thoughts about this?

All in all, whatever keeps your car cooled and fits your pocket, or personal preference, is the right choice, theres no wrong ones. I myself have two SPAL electric fans, ive aready done all the wiring under the hood, but still im contemplating with myself should i sell them and buy new thermal clutch setup and shroud. My reasoning being only the looks. as funny as it sounds. Its just "part of the package" for me.

Please discuss, and if you have something to point which is wrong, i happily edit it.

 

The "butt dyno" will always register an improvement after one has expended time and money on a mod.

 

Flex fans are a waste of time, they save power by moving less air, even at low speeds. Thermostatic clutch fan is all anyone needs with a longitudinally mounted engine that can drive it off the water pump, fewer energy "losses" than an electric fan.

 

If an electric fan is not drawing electrical power is isn't a load on the engine. The main drawbacks as I see them are;
Cost.
Complexity.
Mounting them so as not interfere adversely with airflow. I'm not talking about cars which left the factory with electric fans, the designers and engineers would have gone to considerable trouble to make sure this isn't a problem.

To get the stick out to beat this dead horse again, it seems most aftermarket fans are added in an attempt to fix another fault, mostly the radiator partially plugged, or not up to the job with a modified engine. Clutch fans are a simple and effective way to keep old fashioned front engined rwd vehicles properly cooled.
Farm tractors and other slow moving vehicles on the other hand need a fixed fan to keep sufficient airflow through the radiator, as would stationary plant.

Roger.

 

Engine masters season 2 dyno tested a 350 hp small block Chevy

NO FAN ( like an electric fan ). ...... 349 hp

Fan clutch Mech fan LOST 14 hp

flex fan and standard fixed fans lost almost 30 HP!!

that was reviving to ~5500 or so The more you rev the more loss / drag. Puttin around won’t make much of a difference. Drag racing winding her up ...big difference. High revving motor going over 6k , bigger difference.

interesting real dyno back to back testing. They mentioned and theorized that it’s a fixed number and not a percentage.

 

Ironically, I just watched that episode a couple of days ago. First thing that came to mind is that they seemed to imply that the electric fan doesn't produce any measurable HP draw on the engine. If that were true, you'd have a free power source. It takes a certain amount of HP to produce the amperage needed to drive the electric fan. Second, they didn't do anything to compare fans of equal cooling ability. I doubt the metal "flex" fan moved as much air as the clutch fan, or even the plastic fan.

 

Great post, thank you for this.

I have been trying to piece together for quite some time exactly where 90 HP is consumed by my 350 when stock, going gross to net. I even have a list made up with possible HP losses due to certain components. I had the clutch fan down for 5 HP... I may open a thread with the list and ask you guys to have at it. Hopefully whittle it down to a realistic assessment.

 

Where do you get 90 HP? In 1971, the first year automakers changed from SAE gross to SAE net HP numbers, Olds published both the gross and net HP ratings. Gross was no air cleaner, no fan, no accessories, and dyno headers. Net was air cleaner, accessories, fan, and manifolds. The 1971 350 4bbl motor was 260 HP gross and 200 HP net with dual exhaust. at least 25 HP of that was the exhaust manifolds.Another 15 for the fan and the air cleaner and accessories, and it isn't hard to get to 60 HP difference.

 

Joe I love that chart, came across it from one of your postings online a long time ago. Downloaded it many times, on all my devices. It finally provides some clarity where there was none...

I'm guessing my mistake is that I am using the percentage difference rather than the fixed number ?

For example the dual exhaust 350 rated at 260 gross hp is 200 net hp. That is 22.5% less gross to net. So I just took my engines 310 gross hp rating minus the percentage. That comes out to 240 hp net when dual exhaust. Then minus another 20 hp for single exhaust. 220 hp net on my car stock ?

 

The difference from your 310 to the 1971 260 was due to emissions - primarily lower CR, less aggressive cam, and ignition timing. How those differences impacted the gross vs net discussion cannot be known without an SAE net dyno test of a 1969 motor

 

Phil, the gross-to-net difference for each engine family (350 or 455) is relatively constant because it represents the effects of equipment or loads that differ in only a small way depending on rpm or power level. Therefore it is more accurate to use a fixed HP difference between gross and net ratings.

Olds gross-to-net figures are misleading because they manipulated gross HP rating for various reasons.

So lets look at difference between related engines from a theoretical standpoint. An example would compare a 350 310 hp synchro engine versus a 350 310 hp automatic. The synchro cam will reach maximum hp at, say, 300 rpm more than the automatic and the actual gross power will be 280 for the auto engine vs 310 hp for the synchro engine.

• exhaust manifolds and exhaust system-same for both engines; however the additional hp from the synchro cam engine gives more exhaust gas that will increase the gross-net difference by a bit
• air filter-same for both but more power requires additional air which will give more pressure drop and more gross-to-net difference
• accessories-same; but running them at a 300 more rpm will absorb more power that will increase the gross-net difference slightly
• fan-same; but it the extra 300 rpm again absorbs a little more power

In my opinion the gross-to-net difference between those two engines would be in the range of 5 hp.

For confirmation, we can also look at published 1971 gross-to-net differences between engine families for the Corvette, where there was little manipulation of the HP numbers. Small-block Corvette engines gross-to-net differences were listed as 50 hp regardless of power (or rpm at maximum power). Big blocks showed 80 hp difference regardless of power difference of LS5 and LS6. From the analysis above, we know that's not correct, but Chev obviously felt the differences were relatively minor.

 

One of the reasons for electric fans is that, if they are properly sized, meaning big enough to move lots of air, like a dual OEM unit. All the stick on ones from the vendors don't do much. Even if a pair of something like Ford Windstar electric fans (which happen to fit our radiators nicely) use 60 amps, 60Ax14V= 840W. 840w/746w/hp = 1.12HP. Even if the electrical conversion was only 50% efficient, which it isn't, that is less than 2HP. Which is less than 14HP. You do need BIG electric fans, and a 100A+ alternator to make it work. All that being said, if you have a clutch fan, and a shroud, it will keep your car cool just fine as long as your radiator is in good shape. And I was amazed after watching the episode at how well the flex fans didn't work. There is a reason why clutch fans have been in use for 50+ years. They work.

 

Thanks Joe, and that dyno would be a dream. I am a fan of definitive's for certain things. Engine specs is one of them, the fuzziness drives me nuts...

At this point I would settle for a 1969-1970 TH350 310 HP published road test. Preferably from Car Life, as they were highly detailed. I've been looking for that road test for coming on 6 years...

Thanks VC, point understood. Its funny, with my botched reasoning I wasn't that off from what you and Joe are suggesting was a possibility. I estimated the dual exhaust 310 HP at 70 less HP rather than 60, net, and figured the QV cam stick about 10 HP more than my engine.

Now of course this is only an idea right, because maybe the 310 Hp auto was overrated.... frustrating.

Couldn't agree more. My first Olds a 67 Cutlass 330 base options, was 4 blade fixed fan no clutch no shroud. Ran hot often, eventually went with a larger rad, and electric fan. Still ran hot from time to time. My current 69, no issues... factory Harrison brass rad (looks about twice as thick as the 67s original rad) and 7 blade clutch fan with shroud. I will eat the 14 HP loss for that peace of mind.

 

Here are the facts on the 310 hp duo.

The main difference between the two was the cam.

The basic cam grind in the 310 hp automatic was first installed in the 2 bbl 330 in 1964. It had very low lift (0.380"). Over the years they increased the lift 5% and played with the advance. But it remained the second weakest cam Olds ever used (the 75-76 260 cam was the only one weaker).

The cam grind in the 310 hp synchromesh was nearly a match for the W-30 automatic cam, except it was ground retarded to give better low-end in the smaller engine.

There's probably around 30 hp difference between these two engines.