The myth of the electric fan
07-01-2011, 08:55 PM
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The myth of the electric fan I FOUND THIS ONLINE AND THOUGHT I WOULD SHARE WITH ALL THE LS FAMILY IT WAS VERY INTERESTING TO SAY THE LEAST I JUST WENT BACK TO THE MECHANICAL FAN IN THIS CAR I ALWAYS USED THEM BEFORE SO I SEE NO NEED TO CHANGE... http://www.aaroncake.net/RX-7/efanmyth.htm
07-01-2011, 10:03 PM
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Some people over think things. I agree that a clutch fan is very reliable and when the clutch releases there is not much horsepower robbed. Electric fans often give you more room under the hood and can cool the cooling system down when the motor is not running. If you have an electric fuel pump you can really cool the motor down between passes.
In my opinion the fan that is the biggest P.O.S. is a flex fan. They really do rob power and will take a finger off if your not careful.
The thing to remember when using an electric fan is to have some kind of shroud to help pull the air through the radiator efficiently.
In my opinion the fan that is the biggest P.O.S. is a flex fan. They really do rob power and will take a finger off if your not careful.
The thing to remember when using an electric fan is to have some kind of shroud to help pull the air through the radiator efficiently.
07-01-2011, 10:20 PM
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Eh...I don't buy his argument. He makes a lot of assumptions and lets himself off the hook by stating right away it only applies to 2nd gen RX7's.
He seems to say that an electric fan has to draw so much amperage to do the same amount of "work". I don't get that. The major draw s at start up...it doesn't consume a continuous amperage which is why the alternator isn't overloaded and is why the use of a controller or relay setup is necessary.
If electric fans are as worthless as he claims...why would the new car manufacturers use them almost exclusively? Are all of the engineers in the auto industry "mistaken"?
And to say that 200hp needs the same cooling as a 400 hp engine is silly too!
There is just too much odd stuff in that write-up.
I know you aren't trying to start a big argument online (which we all know is useless and retarded) and I'm not trying to be argumentative, but I had to post something!
He seems to say that an electric fan has to draw so much amperage to do the same amount of "work". I don't get that. The major draw s at start up...it doesn't consume a continuous amperage which is why the alternator isn't overloaded and is why the use of a controller or relay setup is necessary.
If electric fans are as worthless as he claims...why would the new car manufacturers use them almost exclusively? Are all of the engineers in the auto industry "mistaken"?
And to say that 200hp needs the same cooling as a 400 hp engine is silly too!
There is just too much odd stuff in that write-up.
I know you aren't trying to start a big argument online (which we all know is useless and retarded) and I'm not trying to be argumentative, but I had to post something!
07-01-2011, 10:27 PM
#4
There are many reasons why manufacturers equip modern cars with electric fans, not the least of which is that they are more efficient. The drag from an alternator producing amperage is far less than the drag from turning a mechanical fan, which can be well over 20HP in larger engines with big fans.
Electric components are generally more efficient than their mechanical counterparts. Hence electric fuel pumps and A.I.R. pumps, then electric fans, and now electric power steering systems can be found in new cars.
Electric components are generally more efficient than their mechanical counterparts. Hence electric fuel pumps and A.I.R. pumps, then electric fans, and now electric power steering systems can be found in new cars.
07-01-2011, 10:36 PM
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We are all here to share info I thought it was compelling to see what some of you guys thought, he has a few holes in his wording but the math holds up. I am a numbers person and i always said the the claims of upwards of a horse or so gains were smoke and mirrors to get you to buy products the key to any fan is the shroud. As far as the manufacturer using electric fans the use them more for space savings then hp savings in fact most of the truck motors we are using to do swaps have mechanical fans. Im sure that GM could have used an electric fan but on a work truck you have the space and you cant take chances on electrical fan malfunction out in the field when your working. An the flex fan is a finger chopper but again there should be a shroud covering it to keep the fingers on the hand.
07-01-2011, 10:41 PM
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No I went back because some one hacked up a build with a fan cluster that was made to cool a baby radiator and the mechanical gives me the same cooling with out the worry of a two dollar part going bad and heating up a motor. If the motor is turning so is the fan. Under the hood of most muscle cars is enough room to retain the factory fan with a little mod on the shroud. Yeah when you pop the hood at the Dairy Queen or the Bobs Big Boy, its not as cool but I prefer function over form. If GM put a mechanical fan on it....... you fill in the rest.
Last edited by boogiewonderland; 07-01-2011 at 10:51 PM.
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07-01-2011, 10:52 PM
#8
I don't know that there is any myth involved with electric fans. However there is a lot of misinformation about them, like they somehow give you free horsepower. It takes energy to move air. If the electric fan is using less energy than it isn't moving as much air. And the more air you move, the more cooling capacity you have. In that respect the potential of a mechanical fan is massively bigger than an electric one because it is being driven by a much larger motor.
His numbers about HP and amps are correct. Electric fans have weak little motors, rarely more than ½ HP (35 amp current draw).
The guy's last paragraph is spot on: there is not much reason to switch to an electric fan if the mechanical is working.
What an electric fan will do is allow you to turn it completely off when additional cooling isn't needed. A clutch fan always has some drag on the motor, but like said probably not much. Electrics are nice because they don’t take up as much space and like someone said you can cool things down between runs. Auto manufactures like them because they simplify building the car, especially with FWD autos. I prefer electric fans as long as they are big enough to cool the car. Their compact size makes it easier to work on the car.
I know from first hand experience that a clutch fan will quit working if you get antifreeze or some other type of lubricant in the shaft. I also know from first hand experience that they will take out a radiator when the bearings go in them and that they aren't much good if you throw a belt. For those three reasons I consider electric fans to be more reliable. I have never had a problem with an electric fan in any car I have ever owned.
His numbers about HP and amps are correct. Electric fans have weak little motors, rarely more than ½ HP (35 amp current draw).
The guy's last paragraph is spot on: there is not much reason to switch to an electric fan if the mechanical is working.
What an electric fan will do is allow you to turn it completely off when additional cooling isn't needed. A clutch fan always has some drag on the motor, but like said probably not much. Electrics are nice because they don’t take up as much space and like someone said you can cool things down between runs. Auto manufactures like them because they simplify building the car, especially with FWD autos. I prefer electric fans as long as they are big enough to cool the car. Their compact size makes it easier to work on the car.
I know from first hand experience that a clutch fan will quit working if you get antifreeze or some other type of lubricant in the shaft. I also know from first hand experience that they will take out a radiator when the bearings go in them and that they aren't much good if you throw a belt. For those three reasons I consider electric fans to be more reliable. I have never had a problem with an electric fan in any car I have ever owned.
Last edited by Pop N Wood; 07-01-2011 at 10:58 PM.
07-01-2011, 11:19 PM
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The major advantage of an electric fan for the manufacturer is space, and the fact that they can control air flow at slow speeds regardless of engine speed. like cruising down main street at a crawl, the engine is only spinning at idle and so is the mechanical fan, with an electric, one or both can be turned on to pull much more air at that speed than a mechanical, taking the driver out of the equation. after about 40 mph i don't think there's a spit of difference between the two, and that's if they are capable of pulling more air than what the speed is forcing through the radiator. IMO if you do a lot of idling at the local bench racing hangout, or cruise pretty slow, then the electric is a bonus. but you say tomato, i say........
07-02-2011, 12:20 AM
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Well to be somewhat honest electric fans are Put in now due compactness of them in certain front wheel drive car or small engine compartment cars and with a mass quantity of them being produced more than one car can have the same fan IMO I think belt driven fans provide more cooling just my 2 cents
07-02-2011, 08:58 AM
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For those 2 or 3 people concerned about the power draw the electric fan pulls from the alternator just before OR during a race... Turn it off, as you'll be going fast enough that you shouldn't need it in nearly any car.
That said, he was specific about the RX-7 (86-92) and thus, may not have been all wrong or all right... Can't tell. Last time I drove one of those was 1988 and I didn't modify it at all... cause it my g/f's car.
Electrics are used today, mostly for space savings. They don't cost less or really move more air and if they did, who should care since the other system worked for decades anyway? The real benefit to racers... switch on, switch off.
That said, he was specific about the RX-7 (86-92) and thus, may not have been all wrong or all right... Can't tell. Last time I drove one of those was 1988 and I didn't modify it at all... cause it my g/f's car.
Electrics are used today, mostly for space savings. They don't cost less or really move more air and if they did, who should care since the other system worked for decades anyway? The real benefit to racers... switch on, switch off.
07-18-2011, 05:57 PM
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http://www.youtube.com/watch?v=1wSQ0vYXX_4 just a little video of what i plan for one of these light well balanced cars for the guy that bashed the rx7 if history has me lost this is exactly what the legend C. Shelby did when he created the biggest thorn in the side of the Europeans and Americans. By taking a AC cobra and shoving some muscle into it. that is the nature and the spirit of the HOT ROD culture...
07-18-2011, 06:48 PM
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I know that serious racers will tell you winning a race is found in 100 tiny things that all add up.
A mechnical/belt driven fan which is always spinning (even a clutch type) is robbing some power, maybe a miniscule amount, maybe 1 hp or less, but it is taking power from the engine.
The beauty of elec fans is
A. When they're off they draw zero
B. The blades are generally much closer to the radiator and consequently more efficient (they're generally better shrouded too)
C. Versatilty, with elec you can have two, you can have a "pusher" etc.
A mechnical/belt driven fan which is always spinning (even a clutch type) is robbing some power, maybe a miniscule amount, maybe 1 hp or less, but it is taking power from the engine.
The beauty of elec fans is
A. When they're off they draw zero
B. The blades are generally much closer to the radiator and consequently more efficient (they're generally better shrouded too)
C. Versatilty, with elec you can have two, you can have a "pusher" etc.
07-19-2011, 06:34 AM
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One thing the electric is great for is for at the track to cool in between rounds. Have a switch to allow you to keep the fan on with the engine not running but in the accessory on the ignition. Turn the fan on and watch it till you car cools to a certain temp. You also need an electric water pump to do this however.
When bracket racing it can make for more consistent times when you have back to back runs by keeping the car the same temp.
When bracket racing it can make for more consistent times when you have back to back runs by keeping the car the same temp.
07-19-2011, 08:37 AM
#19
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I know that serious racers will tell you winning a race is found in 100 tiny things that all add up.
A mechnical/belt driven fan which is always spinning (even a clutch type) is robbing some power, maybe a miniscule amount, maybe 1 hp or less, but it is taking power from the engine.
The beauty of elec fans is
A. When they're off they draw zero
B. The blades are generally much closer to the radiator and consequently more efficient (they're generally better shrouded too)
C. Versatilty, with elec you can have two, you can have a "pusher" etc.
A mechnical/belt driven fan which is always spinning (even a clutch type) is robbing some power, maybe a miniscule amount, maybe 1 hp or less, but it is taking power from the engine.
The beauty of elec fans is
A. When they're off they draw zero
B. The blades are generally much closer to the radiator and consequently more efficient (they're generally better shrouded too)
C. Versatilty, with elec you can have two, you can have a "pusher" etc.
07-19-2011, 09:19 AM
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His arguement is completely flawed.
A properly engineered cooling system will need forced air over the radiater (ie a running fan) at idle and low speed only. An electric fan provides this functionality if the thermostat controls are set right. It will come on at low speed/idle when there is insufficient air throuigh the radiator. At higher speeds ram air will do the job and the electric fan is redundant, and should be off.
A mechanical fan is running at all times, and at a speed proportional to engine speed. It would normally be sized to deliver sufficient air at low engine speeds, and when the engine is running faster the fan is going unnecessarily fast consuming loads of power. The power a fan draws is proportion to its speed cubed. Therefore if he fan is sized to deliver a certain airlfow at 700rpm idle, at 7000rpm the fan will be consuming 1000x as much power!
Taking my car as an example - there is a 20A electric fan, comsuming 240A (1/3 hp). To take account of inefficiencies in the generator lets say this will draw 1/2 hp from the engine power.
If a mechanical fan was installed giving the same airflow as my electric fan (running at 800rpm idle) it would be drawing 1/3 hp from the engine. When the engine is running at max 6500rpm that same fan would consuming 18hp !!
The difference is therefore significant. The electric fan is a much better solution and this is the reason all OEM's have gone this route.
A properly engineered cooling system will need forced air over the radiater (ie a running fan) at idle and low speed only. An electric fan provides this functionality if the thermostat controls are set right. It will come on at low speed/idle when there is insufficient air throuigh the radiator. At higher speeds ram air will do the job and the electric fan is redundant, and should be off.
A mechanical fan is running at all times, and at a speed proportional to engine speed. It would normally be sized to deliver sufficient air at low engine speeds, and when the engine is running faster the fan is going unnecessarily fast consuming loads of power. The power a fan draws is proportion to its speed cubed. Therefore if he fan is sized to deliver a certain airlfow at 700rpm idle, at 7000rpm the fan will be consuming 1000x as much power!
Taking my car as an example - there is a 20A electric fan, comsuming 240A (1/3 hp). To take account of inefficiencies in the generator lets say this will draw 1/2 hp from the engine power.
If a mechanical fan was installed giving the same airflow as my electric fan (running at 800rpm idle) it would be drawing 1/3 hp from the engine. When the engine is running at max 6500rpm that same fan would consuming 18hp !!
The difference is therefore significant. The electric fan is a much better solution and this is the reason all OEM's have gone this route.
