any point in an electric fan?

[Anonymous]

A buddy of mine stands for a moment looking into the engine bay of my 62 Falcon with a 200/6. He tells me that I'd gain 15hp by getting rid of my belt driven radiator fan and moving to an electric fan instead.

"All the gearheads do it," he claims.

I think he's full of it. Certainly there is a little bit of drag on the engine moving the fan around, but it seems an efficient enough design to me.

Any thoughts?

 

[66 Fastback]

IMO, 15 HP is a pretty big stretch. I would guesstimate that it is a fraction of a HP.
The commercial fan in the linked picture below is less than 1 HP.
http://www.electricaldeals.com/html/sea ... d1=EMC&d2=

There ain't no free lunch. A large dual electric fan setup will pull up to 30 amps. If your electirc system is operating at a high 15 volts, then that still only translates into 0.6 HP. The alternator is still going to have to come up with that power sometime when it is running.

The belt also drives the water pump which will probably have a slightly larger load than the fan. Unless you plan on building a drag race car and wire the alernator and battery such that the fan and pump only run off of the battery and the alternator does not provide power to the fan / pump during the run, I would not bother.
Doug

 

[rbohm]

8) actually 15 hp isnt out of the realm of possibility. in order to draw enough air the mechanical fan has to have a pretty severe pitch to the blades, that that creates drag. using an electric fan frees up the power that it takes to drive the mechanical fan. yes it does take 30amps to run an electric fan, but since you have a net gain in power, it is a worth while addition. the other advantage of an electric fan is that is runs only when needed, unless you have it set up to run all the time the ignition is on.

 

[Lazy JW]

The stock fan won't pull any where near 15 hp. As 66 Fastback noted, 30 amps at 15 volts is only 450 watts, or just over .6 hp. You could mount a stock 200 fan on a 3 hp Briggs & Stratton and it would still run up into the governor with power to spare.

However, a gain is still a gain. Is it worth it? I dunno. Only you can decide. I would have to get the parts mighty cheap before I would do it.
Joe

 

[wsa111]

The electric uses very little energy to operate.

A year ago or so one of the magazines ran tests to determine which mechanical fan consummed less energy & a thermostat clutch fan used less than just a clutch fan.

A fixed fan will rob you of the most power.

The difference in power lost is more than you think.

I would guess an electric fan will give you at least 5 more HP, possibly more especially if you have an engine you twist to 6000 rpm's.

If anyone recalls that article please post the magazine which did the tests.

Go electric, Will

 

[Lazy JW]

My former boss used to burn brush piles on timber sales after the logging was done. He had a fan at least 24" diameter mounted directly on a 5 hp Briggs & Stratton engine that he used to fan the flames. The whole thing was mounted on a little cart that he could push around and set up wherever. It would spin that fan at full governed speed, and I know for absolute certain that it was a whole lot more fan than a stock Ford unit.

But 5 hp is still 5 hp. Electric fans make a lot of sense for vehicles driven short distances. In cool weather the fan may never run.
Joe

 

[fxp]

Interesting thread (for me at least). The idea that an electric fan should be more efficient (in terms of power consumed whilst in actual operation) than the fixed fan seems to defy the laws of physics (assuming both move the same amount of air). With the fixed fan you are harnessing the turning energy of the engine to also turn the fan - you've got the load of the fan moving the air and any friction losses in the belt converted to heat.

With the electric you've got to convert the motion of the engine into electrical energy at the alternator which is not 100% efficient and has similar friction losses to the fan, transmission loss getting the power to the battery, storage losses in the battery, transmission losses getting the power from the battery to the fan motor and then losses converting the electricity back into motion in the motor all before you get to the actual load of the fan moving the air. Some of these losses are tiny granted, but they all add up, so an electric fan moving the same volume of air must be less efficient than a fixed fan unless I'm missing something.

Where it becomes more efficient is in the fact it is only on where needed as has been noted, which is why you want one. Cruising in clear air in moderate temps will see the thing off and so clearly more efficient than the fixed fan. Sitting in traffic on a scorcher will have the thing spinning at max to cool your engine and using heaps more power than the fixed (but also cooling more efficiently than the fixed which is spinning at your idle speed and so doing bugger all).

All of that would seem to say to me that it's nothing like a simple one is better than the other or that you would automatically gain xHP from the conversion. If you drive around in a lot of traffic in a hot climate I can't see how you can avoid using more energy with the electric (but also keep your engine from blowing it's top). If you do heaps of driving at speed you'll gain a little from not having the thing on. I'd love to have all of the above disproved by someone with more knowledge than myself, but the bit I did pick up in physics class would seem to indicate that any gains are likely to be negligible and highly dependent on how the car is used.

 

[Lazy JW]

... I'd love to have all of the above disproved by someone with more knowledge than myself, but the bit I did pick up in physics class would seem to indicate that any gains are likely to be negligible and highly dependent on how the car is used.

I think you have it pretty well figured out. We are really comparing apples to oranges and it just doesn't work to do that.

Most electric fans are single-speed. The fixed mechanical fan is variable speed, and since drag increases with the square of velocity it is pretty easy to see how those huge power consumption numbers are generated. A stock fan turning 8000 rpm is going to create a LOT of drag. The electric fan will never increase drag regardless of how fast the engine spins.

There ain't no free lunch here, but the electric fans do have merit, especially when they aren't running.
Joe

 

[fxp]

Yeah that makes perfect sense, and the difference in drag at high revs was a variable I didn't factor in. There is a clear reason for a HP gain for an electric in that circumstance and so would seem to be a bit of a gimme to ditch the fixed fan on a high reving racer.

For more 'normal' driving conditions there may be advantages in going electric depending on your car and it's uses, but extra ponies are unlikely to a significant one.

 

[66 Fastback]

My point was that 15 HP gain on our stock engines is not realistic. Maybe bigger engines that rev at higher rpms could realize a significant savings. But even if our fan was 10 times less efficient than what I calculated, you still only have 6 hp.
Doug

 

[ASMART]

1 point: The example of a B&S engine turning a fan did not take into account the RPM at which it was turning. I am no small engine expert, but I would be surprised if a B&S engine ever did over 2000RPM. Since wind resistance starts to increase exponentially at a certain speed, a large horse power loss at higher RPM is believable.

 

[fxp]

Agreed on both counts. At high RPM the load becomes very significant, but, our engines aren't going to make those high RPM without some serious mods.

To compare better you'd need to know what RPM the electric fan does. Again assuming the design of the fan blade itself isn't a significant variable and discounting the losses converting to electricity and back then you can say with reasonable accuracy that the fixed fan gives an increase in HP over the electric (when it's on) at RPM below the fan speed. Above that the drag on the fixed fan is going to be increasing significant.

If we start with Doug's 0.6 HP calc for the fan and assume it's doing 2000RPM (I tried looking under the hood of my 96 and couldn't find a fan rating, but they must be doing at least that surely) and for the sake of a neat calculation assume the fixed fan costs about the same at 2000 rpm (and that the increased drag is the only significant load variable), then at 4000 rpm the fixed fan will be costing you about 1.8HP over an electric (with the fan on). Double the revs to 8000 and the loss jumps up to 9HP, but there aren't many of us getting those sorts of revs. At 6000 the jump up is only to 4.8HP. As Joe said it might be worth the effort to some folks to harness that 5HP but 6000 is waaaaaay beyond the limits of my 170 so if I did go for an electric fan it would be for a very different reason.

A 15HP gain at say 8000 is feasible if the electric is doing about 1600rpm rather than the 2000 assumed. So it would be interesting if someone has a fan speed rating we can go off.

They're pretty rough and ready calcs but it would seem you need to be making pretty high revs to see 15HP.

 

[Anonymous]

Several years ago Car Craft did a dyno test on different types of factory and aftermarket fans then dyno'd an electric fan.

The electric fan gained almost 15 hp and the other fans gained anywhere from 7-14 hp over the stock fixed blade fan.

The engine dynoed (of course) was a small block Chevy.

As soon as I find my HotRod Bill is talking about I'll post the results.

Doug

 

[Lazy JW]

1 point: The example of a B&S engine turning a fan did not take into account the RPM at which it was turning. I am no small engine expert, but I would be surprised if a B&S engine ever did over 2000RPM. Since wind resistance starts to increase exponentially at a certain speed, a large horse power loss at higher RPM is believable.

5 hp B&S engines are governed at 3450 rpm.
Joe

 

[Jamie Miles]

All stock Briggs engines, regardless of horsepower, are governed at 3600 RPM. Modifed, they can turn up to around 7,500 with the stock rod and flywheel. More then that, and you got to start looking into aftermarket billet parts. There is a huge following of the 5hp B&S tiller engine in Kart racing.

As for electric fans, I am going to run one on my '69 1/2 Maverick. This is a car that will see alot of highway driving, when a fan isn't really needed. A while back, I took the stock fan off my '72 Maverick and ran down my neighborhood and back. There was a noticeable "seat of the pants" diffrence. Enough to convince me it was worth it to run one on the next car I build.

 

[xafalcongs]

There are many newer electric fans that draw 1/2-2/3 the amps of older fans while still moving equal amounts of air. Also, there are now variable speed thermostat switches that will allow the fan speed to increase and decrease according to water temps. Check the websites of the major companies, you'd be surprised at what they have been releasing lately.

 

[Anonymous]

Very well. I'll sign my Falcon up to be the test subject. Going into this feet first, let say for the sake of propriety that my Falcon is exposed to a variety of driving conditions, which seems to be one of the factors involved with any benefits gleened due to physics, airflow, drag, style of driving. I'm a contractor, so my job is basically to drive around Portland and solve problems all day. I spend a good deal of time in traffic, I spend a good deal of time on the highways.

What would aid me the most, now that I have everyone's attention, is what setup should I buy? I would rather buy an off-the-shelf fan/thermostat/whatever setup than spend a few hours at the junkyard not finding what I'm looking for. Remember, I've got a round body Falcon, so space is something of an issue.

 

[rbohm]

8) spal and flex-i-lite are two of the better electric fans on the market. i like the spall fans myself. look for a fan that pulls about 2200-2500 cfm of air. spal does have some slim line fans that will fill the bill nicely. as for a fan controller, spal has you covered there as well. you can order either a set control that turns the fan on at like 195 degrees and off at around 180, or you can get a variable controller that you can set the on/off temps to your liking with in the controllers range. the wiring harness foir the controller should come with a relay to send current to the fan. if it doesnt, then wire in a relay, simple to do.

 

[MustangSix]

A couple of years ago there was a dyno test published that compared various losses for different types of fans. This was done on a Mopar v8 with a fairly large fan, but the hp loss was significant, ranging from seven to 15 hp, IIRC. The worst offender was some large aftermarket flex fan, I think, with the best of the batch a stock thermal clutch fan.

Point of the story was, you could recover up to several horses by replacing the stock fan with something more efficient, like a clutch or electric fan.

 

[lyonsy]

hey
on engine's ive had on chassie dyno's ive seen a 5hp gain in running thermo's to a pump driven fan.
but had to install the pump driven to keep the engine cool when racing (dirt track).
drift