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Old January 23rd, 2010, 09:30 PM   #1 (permalink)
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Here's a video of my car from launch http://www.youtube.com/watch?v=jeZAoQg035w
How much horsepower gained by using electric fan

Realistsically, how much hp is gained by using an electric fan, verses using the stock fan and fan clutch? Anyone have any real world experience making this changeover?
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Old January 23rd, 2010, 10:16 PM   #2 (permalink)
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Not enough to notice. Maybe 5-10hp.
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Old January 24th, 2010, 06:04 AM   #3 (permalink)
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As Andy said you prob. won't notice the HP. You may notice a slight change in fuel economy and engine temp.
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Old January 24th, 2010, 07:15 AM   #4 (permalink)
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Not enough to notice. Maybe 5-10hp.
Has anyone actually ever measured this?

The thermodynamics person in me is bothered by this. Whether you get the energy to turn the fan directly from the engine by connecting it to the end of the crankshaft or get it from the engine by turning some of the engine's energy into electricity first, you're still getting the energy from the engine. Is the electricity route more efficient? My first guess would be no, because, with the first set up, you're getting the most direct transfer of energy possible.

For electricity created by the engine, losses are going to occur in the fan belt that turns the alternator as there is certain to be some slippage, however minor, as the belt ages, there are inefficiencies in the alternator itself in the conversion of mechanical energy to electrical, and there are voltage drops in the wiring connecting everything together. All of these losses might be very tiny, but none of them would make the electric fan MORE efficient. They would all work against you.

Am I missing something?
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Old January 24th, 2010, 08:08 AM   #5 (permalink)
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Yes it has been tested and proven by every auto manufacturer on the planet. Thats one of the main reasons why most cars have been switched over as mechanical fans are a constant load on the engine even with a viscous clutch while electrical fans can be controlled and only turned on when needed.

However mechanical fans do have there place though. In many cases they are able to move more air than their electric counterparts which is why you will still see them used in many truck applications.

Most manufacturers will be switching over to 100% electrical accessory drive very shortly with no mechanical connection to the engine for things such as water pumps, PS pumps or A/C Compressors. Most are slated to go to a 40+ volt system very soon.
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Old January 24th, 2010, 08:14 AM   #6 (permalink)
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I know of this same subject on another board, I could post a link to it.
But it turned into a big pi#$^% match. (you know...the other guys)
if you read through the B.S. there was some good info there.
let me know
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Old January 24th, 2010, 08:24 AM   #7 (permalink)
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It will always take X hp to move Y CFM of air to provide cooling regardless of whether the fan is mechanically or electrically driven. The mechanical to electrical conversion in the alternator to drive the electric fan is not 100% efficient, so the engine will have to make slightly more power to provide the electric fan the same horsepower.

The HUGE advantage of electric over mechanical is the ability to turn them off when not needed or desired which is not technically possible with a mechanical fan even if equipped with an electro magnetic clutch. Many modern vehicle turn off all large electrical consumers including the fans when they see WOT to allow for better acceleration.
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Old January 24th, 2010, 08:50 AM   #8 (permalink)
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It will always take X hp to move Y CFM of air to provide cooling regardless of whether the fan is mechanically or electrically driven. The mechanical to electrical conversion in the alternator to drive the electric fan is not 100% efficient, so the engine will have to make slightly more power to provide the electric fan the same horsepower.

The HUGE advantage of electric over mechanical is the ability to turn them off when not
needed or desired which is not technically possible with a mechanical fan even if equipped with an electro magnetic clutch. Many modern vehicle turn off all large electrical consumers including the fans when they see WOT to allow for better acceleration.
I believe you are correct.
the amount of H.P. difference it takes on most street cars is not worth the cost of
changing over just for the H.P.

I can turn my electric fan and alternator on and off from inside the car.I have made back to back passes at the strip with both on,one or the other on,and both off.With
not much change in E.T. maybe .002. this is on a car that runs 12.2s-12.4s in the 1/4.
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Old January 24th, 2010, 09:51 AM   #9 (permalink)
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The higher the amp draw required by the alternator when operatoring electrical loads will require more hp to turn the alternator. The alternator acts like a brake when under load. A good example of this is the re-generatoion braking used on golf carts, when you let off on the trottle the golf cart slows down quickly as the motor switches to a generaor to charge the batteries. That same force occurs with the alternator as load increases. The only hp gain from mechanical to electrical is a stated above when you shut the load off.
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Old January 24th, 2010, 10:38 AM   #10 (permalink)
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mechanical fans are a constant load on the engine even with a viscous clutch while electrical fans can be controlled and only turned on when needed.
OK, so it's an issue of turning the fan off when not needed, which is easier to do with an electric one. I asked if I was missing something. The answer was yes.
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Old January 24th, 2010, 10:42 AM   #11 (permalink)
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Something else to be considered here is weight. Electric fans weigh almost nothing where a clutch fan weighs a ton.
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Old January 24th, 2010, 02:03 PM   #12 (permalink)
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Thats one of the main reasons why most cars have been switched over as mechanical fans are a constant load on the engine even with a viscous clutch while electrical fans can be controlled and only turned on when needed.
The real reason is that it's very difficult to put a mechanical fan on an engine that sits east-west.
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Old January 24th, 2010, 03:23 PM   #13 (permalink)
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Its a valid point but worldwide there are still more engines longitudinaly mounted than transverse and the majority of those are running electric fans.
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Old January 24th, 2010, 05:53 PM   #14 (permalink)
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I recently answered this same basic question on another forum. About 8-9 years ago, I chassis dyno tested a lot of modifications on my Cummins Turbo Diesel Dodge. Going from the stock heavy duty, stiff clutch fan to no fan at all gave 4 HP when testing at 600 HP at the rear wheels.
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Old January 24th, 2010, 06:57 PM   #15 (permalink)
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If you reduce rotating mass to the front of the engine. Even thou a greater load is required from the alternator. Reduction in weight would produce a greater gain than the stain on the alternator. You can always put an alternator that produces more amps on your engine. If you have noticed most racers only have an alternator that is turned by the engine.

They use electric fan, water pump, and manual steering. It not because it looks cool. It because it serves a purpose. The usage of this will increase power made by reducing rotating mass which means engine can produce more power. Which means a lower ET.

I would have explained it like this before, but it was 1:16 am when I answered the tread the first time. The only thing on my mind was sleep.

Would I use electric fan on my Cutlass, no it's going to be a driver and doesn't require me to use one. I will use a clutch fan. Not because it was factory it's because I like it on a street car. On a car that I race yes.
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Old January 24th, 2010, 07:15 PM   #16 (permalink)
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Everything sounds good, but the thermodynamicist in me still needs to chime in.

Quote:
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You can always put an alternator that produces more amps on your engine.
You can't get something for nothing. If you put a larger alternator on, it takes more power from the engine to turn it, so doing so costs you power, however small the amount. If this weren't the case, then we could put any size alternator on and power our houses and factories and cities, too. We'd have, in short, a perpetual motion machine, which violates the first law of thermodynamics (conservation of energy).


Quote:
They use electric fan, water pump, and manual steering. It not because it looks cool. It because it serves a purpose. The usage of this will increase power made by reducing rotating mass which means engine can produce more power.
Again, be careful. The engine is always producing the SAME amount of power unless you modify the engine itself. It's just that, with only the alternator being turned and no power steering or water pump or fan, there is more NET power coming from the engine and available to move the car. Some still gets used up in powering the electric fan and water pump.

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Old January 24th, 2010, 07:39 PM   #17 (permalink)
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I didn't know that building muscle cars, hot rods, and race cars had anything to do with the conservation of energy. If you want something that conserves energy than buy a Honda. Which by the way uses a electric fan.
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Old January 25th, 2010, 04:58 AM   #18 (permalink)
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I didn't know that building muscle cars, hot rods, and race cars had anything to do with the conservation of energy.
Well, maybe you've learned something then.

One could argue that racing is more concerned with conserving energy than most anything else one could do except maybe run a power plant.

You have a fixed amount of energy coming from your engine, and it all has to go somewhere. You want to as much of it as possible to go to the wheels, where it does you the most good. So you're constantly doing things to improve the efficiency of the necessary but power-sapping accessories that draw power from the engine, like the cooling system and electrical system. A plastic fan that runs only when you need it is more efficient than a metal one that weighs more and spins all the time, whether it's needed or not.

Ditto for the water pump, although I think there is a greater limit to what you can do here because, regardless of HOW you pump the coolant, the main thing that determines the energy for this is the energy needed to move the coolant itself. That's not going to change unless you change to a different type of coolant that has a different density or heat capacity. But for a constant type of coolant, the energy to move it around in the engine is the same no matter how you move it. So, for example, if you can use a plastic water pump instead of a metal one, you can save some weight and therefore gets some energy improvement.

You need an alternator to generate the electricity needed to run the electric fan, water pump, and so forth, but each amp you ask it to produce costs you something, so you want to run with the smallest-capacity alternator that will do the job.

I could go on, but the bottom line is, while they may not realize it, race car people live, eat, and breathe the law of conservation of energy. It's who is the most efficient with their energy that determines who wins the race.

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Old January 25th, 2010, 05:25 AM   #19 (permalink)
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IF you put an electric fan on your engine it will look cool and be cool. The easiest place to find a good electric fan is the salvage yard. Look for a mid 80s full sized truck or van.
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Old January 25th, 2010, 07:37 AM   #20 (permalink)
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Jaunty I think you like over thinking things. Yes when building a race car the builder does consider energy usage. I know I have built many, but even after building a car the builder will spend a lot of time at the track with car. On test and tune nights. Changing out parts finding out what parts work and doesn't work.

A plastic water pump I haven't seen one. I have seen many aluminum ones.

As far as alternator having one that larger capacity would only require maybe a couple more hp to turn it, if it allows you make changes that gain 25hp than I say it would be worth it. Granted the car won't need a big alternator.

Your last statement I do like it. Most do realize I know I do, but this is only part of the build. A lot more goes into it.
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Old January 25th, 2010, 07:47 AM   #21 (permalink)
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Jaunty I think you like over thinking things.
I'll take that as a compliment! Actually, I love overthinking them. That's why most people find me so irritating.
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Old January 25th, 2010, 08:07 AM   #22 (permalink)
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FYI the fastest car I ever built had power steering pump, stock water pump, clutch fan, mechanical fuel pump, and full interior. It ran 5.62 at 120mph 1/8 mile track. I drove it to the track.
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Old January 25th, 2010, 06:32 PM   #23 (permalink)
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If you are running a stiff fan you may gain some hp,fan running all the time.If it's a clutch fan I would say you would are gain any hp.Alternator will take about 10 hp whencharging full load 60 amps.
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Old January 25th, 2010, 06:34 PM   #24 (permalink)
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would not gain any hp
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Old March 5th, 2010, 12:54 PM   #25 (permalink)
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http://www.aaroncake.net/RX-7/efanmyth.htm

this site claims theres little if any gain, and the main reason for switching to electric is cheaper cost compared to repairing a clutch fan
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Old March 5th, 2010, 02:41 PM   #26 (permalink)
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Back to back dyno sessions proved (on one specific motor) a little under 10hp gain without a 4 blade fan (not clutched). This is on a race engine. In order to calculate the savings you need to know the specifics of your alternator and electric fan both. The combination above gained 5 HP based on a specific alternator and electric fan combo. That is 5 hp when the fan is on, 10hp gain when fan is off.

You can not claim it is net zero without knowing the current draw of the fan and the efficiency of the alternator. If i recall a rough rule of thumb is that every 30 amps an alternator generates requires 1hp but dont quote me on it because its been a while since i did this.

It is possible to have a fan alternator combo that is more efficient than a water pump driven fan - either in net or average hp difference.
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