Mindspin311

Is there any truth in this? It seems logical since you wont have the regular fan connected to the eshaft so there would be a bit less loss going on...

SirCygnus

iTrader: (1)

but electrical power is drawn from the alternator thus creating the same resistence.
the more power being drawn form the alt, the more resistence is it has in order to spin it. so...



no.

CyberPitz

http://www.aaroncake.net/rx-7/efanmyth.htm

Aaron Cake

iTrader: (1)

This is covered in the FAQ.

KNONFS

iTrader: (14)

I don't buy that, the alternator will spin the same amount of RPM, will have the same resistance and will put out the same amount of amps wether you are running an efan or not.

CyberPitz

Read that link I posted, it will give you all information you need to buy it

KNONFS

iTrader: (14)

No need to...

As I said, nothing asides from pullies will affect the alternator RPMs, amps output, or resistance.

lax-rotor

iTrader: (1)

About the only thing you gain off of a stock clutch fan is room. If you want you can check out my project to see what I mean. You'll definatly put strain on the electrical system, but other than that you just gain room to work and the ability to run whatever you want through about 3 cubic feet or more.

rx7racerca

iTrader: (1)

What's not to buy? The stock fan is clutched, so it freewheels when cooling needs are low - typically when cruising, so that air is moving thru the rad - no advantage to an e-fan there. When the e-fan is on, in order to do the same work cooling, it must necessarily get the energy from the engine - via the electrical system. There's no free lunch here - energy drawn on the electrical system to perform the work of cooling necessarily translates into load on the engine, via the alternator. In fact, given that an e-fan is converting the mechanical energy of the engine to electrical energy (whereas the stock fan uses the mechanical energy directly), then converting it back into mechanical energy (rotating fan drawing air), it will necessarily be the case that the e-fan will take more engine energy to do the same job, due to the inevitable energy losses that happen when converting from one form of energy to another. The alternator's resistance most emphatically does not remain the same with the load of an e-fan, it goes up, a lot.

The problem of an e-fan using engine energy less efficiently than the stock, working clutch fan is compounded by the fact when cooling needs are high - eg, idling in traffic - , the alternator on these cars barely keeps up with demand just to run the engine electrical system, lights, and so on. Ever noticed how just hitting the brakes when idling hot causes the revs to sag, then return to a slightly higher point? That's because just the load of the brake lights on the alternator slows the engine significantly - proof that load on the alternator makes the engine work harder. The surge that follows the sag is an idle compensator, just like for the A/C, that Mazda designed in, recognizing that at electrical loads at idle tax the alternator/charging system. An e-fan is going to tax the charging system further precisely when it is least able to compensate - low engine/vehicle speeds.

Aaron Cake

iTrader: (1)

The alternator is not a free energy device. If you draw more current from it, then the shaft becomes harder to spin, and the engine must work harder to spin it.

The alternator only supplies the amount of current that the car is drawing...That is, a 70A alternator does not always "push" 70A out into the electrical system. If the electrical draw from the car is only 50A, then only 50A will be produced from the alternator.

This is why cars with flakey (or missing) BAC valves have idle dropping issues under heavy electrical load. Switching in a high current item like the headlights, defroster grid or e-fan causes the idle to fall as the load on the engine increases.

KNONFS

iTrader: (14)

Harder to a certain point, right?

If i was to follow your theory, a stock FC with a 90amp sound system, e fan, AC & headlights on; will barely move...


I am not going to lie, since i don't know if thats true or not; however I know that has RPM increases, so do the alternators amp output.

Yes, as load to the engine increases.

Aaron Cake

iTrader: (1)

The relationship between how hard it is to turn the shaft vs. how much current is drawn from the alternator is basically linear. The shaft becomes harder to turn as you draw more current, up to the maximum current the alternator can produce. If you had a weak source of mechanical power (small engine, human) then you could draw enough power to drag the shaft down to the point where it could not be turned...Actually 90A at 12V is only 1080 watts, or about 1.3 HP. Most humans could provide this much energy for at least a few minutes...

I'm not sure what this means...Also it's not a theory, but elecromechanical fact.

Yes, because more mechanical energy is being input into the alternator.

KNONFS

iTrader: (14)

THANK YOU!

So in conclusion an e-fan amp draw is next to nothing or in the decimal range. If 90amps is equivalent to 1.3hp; then 45amp is equivalent to 0.75hp.

So in reality an efan might cost you what, 0.35hp? A couple of things come to mind, can't think of a single person that can notice the difference between 0.35hp. The second thing that comes to mind is, the loss of HP on an efan setup cancels out with the extra weight that the eshaft is carrying with the stock fan setup, and\or any drag that it might cause on the engine.

TitaniumTT

Yeah but if the stock fan absorbs 18hp (exageration) and the electric one which in reality draws ~15A running, then you would be gaining a decent amount. But what someone needs to do is head over to a dyno and make 3 runs, get an average, remove the stock clutch fan and make 3 more runs and take that average and that might give a good indication of how much energy it takes to drive the clutch fan, than inverse the drivetrain loss to get RWHP... anyone wanna take a guess?

KillaKitiie

Damnit i never thought of it like that!! Thats pretty cool.

RX7 7777

would it be worth it to take out my a/c pump during the summer is it worth the power or not?

KillaKitiie

if it works keep it,if not have a shop remove it that can do it right...the A.C weigh's a ton.

RX7 7777

is it worth taking out my A/C pump for more power or would i just rost in my car?
Thanks

RX7 7777

thanks for the info

CyberPitz

I wouldn't take it out if it works. It's not enough to give you enough HP, if it's just sitting there....that's like taking out the carpet in your hatch and expecting a 10 hp gain :p

Aaron Cake

iTrader: (1)

Basically, yes. But neither does the mechanical fan. That's sort of the point I try to make in the writeup. If the mechanical fan really did draw several HP, several HP worth of electrical power must be drawn from the alternator to do the same physical work (ignoring differences in fan blade efficiency based on different designs). So in truth neither one really takes that much power...

The clutch fan freewheels when it's not needed, so there is no serious drag on the e-shaft.

ziplock

rx7racerca knows whats up

KNONFS

iTrader: (14)

I am against the e-fan draw HP mentality; and what I am trying to prove is that it doesn't draw any power (well maybe 0.25hp). Notice that I am not claiming that the efan gives more HP; just that itd not how some want to put it...


When talking about drag, yes you are right; however its weight will always be a burden on the e-shaft.

Whizbang

the reason i opted for the electric fan was the room that it made in the engine bay.

classicauto

iTrader: (3)

I did my e-fan setup coz all tha mad powah comes fRUM da fanz yo.

I SWEAR I'VE SEEN A THREAD LIKE THIS SOMEHERE BEFORE???