So I've been reading up on getting an e-fan, I know a lot of the guys on the forum have them and its supposed to free up horsepower and improve mpg. But I read that you just pretty much draw the power from the alternator now which is gonna make the alternator take more power from the engine ...soo there might not be a point? Anyone have solid proof getting an e-fan makes a difference? And I know some of the reason it's supposed to be better is because I can turn it on and off, but if its only better when it's off then I don't think it's really worth it

 

I have no dyno numbers on my application with just the efan added. The only dyno after efan had many other performance boosters for the numbers to be of use for this topic.

But I will say that there is NO QUESTION my low rpm acceleration is without a doubt quicker. There is no doubt in my mind I have to give less throttle when sitting still to come up to speed. Less throttle pressure equates to better fuel economy.

MPG numbers aren't going to be a make/break situation. You'll gain a little in stop/go driving but when the RPMs are up enough that the clutch fan isn't a drain on the engine then there would be no measurable difference.

As for the Alternator drain theory - I get it and there is some merit here. BUT that depends on the fan. Some of these Furd "pick 'n pull" fans can draw up to 70 amps or more. But my Flex-a-Lite only has an 18 amp max draw. No problem for a 130 amp alternator to absorb unless you are running a couple thousand watt amps and carnival lighting on your truck.

Neither reasons you state are why I went to an efan.

I went that route because when off-road, going over VERY SLOW terrain (like when I'm hog hunting) and the temp is deep-south HOT - I was tired of watching my temp needle climp well over 200*. Sometimes I'd be going barely over idle speed for a few miles in 100* heat and the clutch fan just couldn't cut it.
Because my efan pulls a constant 3300 cfm - regardless of engine RPM - my engine stays at or slightly above my t-stat opening temp ALL THE TIME now, regardless of how slow/fast I may be going.

 

So it obviously helped you out but I'm thinking about it for 20-30 miles highway driving everyday if its not gonna help me in gas mileage than I don't think it's worth it for my situation, I live in south Florida and it gets pretty damn hot but I'm not really worried about that

 

1 horsepower = 745 watts.

If your fan is taking 1HP away from the engine, then it will take 745W of electrical energy to compensate.

745W/12.3V = 60A

so 1 horsepower taken by the mechanical fan will require 60A of electrical power from the alternator to power an electrical fan. through some mathematics that I can't remember off the top of my head we can convert an electrical fans current draw back into mechanical energy, and thus electrical power and horsepower and determine if an electrical fan is going to save any horsepower.

off the top of my head I'd say that may be the case because I don't think an electrical fan is going to draw anywhere near 60A to run.

 

Actually, thinking about this I would say an E-fan saves horsepower.

I don't know how much horsepower the mechanical fan robs, but if it takes at LEAST 1hp away from the engine, that means an electrical fan would need to draw 60A in order to rob the same horsepower from the engine as a mechanical fan.

So if an electric fan draws 10A @ 12V than it's only pulling (12V*10A=120W) 120W of power.

(120W/745W)*100=16%

So the electric fan only needs 16% of the power required to run a mechanical fan IF the mechanical fan only robs 1HP from the engine.

In my mind this works out to an E-Fan adding horsepower.

But in order to really know we need to know how many HP the mechanical fan "costs" to run.

 

12V*18A=216W

(216W/745W)*100=29% of 1HP

Given that we don't know how much HP it takes to run the mechanical fan, but assuming that it takes more than 1HP, you're saving at LEAST 71% of the power needed to run the mechanical fan.

I think it's pretty safe to assume the mechanical fan uses at least 1HP, given the frictional loses of the fluid within the fan clutch and frictional loses caused by the blades moving through the air.

Lets not forget that the amount of power used by the mechanical fan is going to change based on temperature and RPM of the engine, as the engine RPM increases thus does the speed of the fan and as the speed of the fan increases so does the drag on the blades which in turn creates more friction and the requirement of more mechanical power to drive the fan.

sorry, I got all engineering up in this ****, I could be wrong on a few aspects, but I'm fairly drunk and could easily be missing something, but I'd welcome the technical debate to help narrow this down to a precise number.

someone needs to run a truck on a dyno, then remove the fan and do another run. the difference is how much HP the fan takes.

 

I've never actually seen it explained mathematically. That is curious and good to know. I'd be interested in seeing the real numbers, too. I've got a Flex-a-Lite still sitting downstairs I need to install...

 

some of the best gas mileage i have ever got was with the stock clutch fan installed. now i do have to say i like the electric fans. they made my 81 pretty silent and i think it would allow my engine to warm up quicker which i think is suppose to help gas mileage but i have yet to see any increase. the only time i even have to turn my fans on is when in traffic. as long as i am moving it is find and i never need them.

 

The motor warms up at the same rate, regardless of the fan type.

 

oh my god..... I have absolutely no recollection of even reading this thread, let-alone breaking down the mathematics of it all.

This is why no one drinks with me.