What's the deal with E-Fans?

[l008com]

So before we get into specifics, I'm still a little confused on the basic concept here. It seems to be "common knowledge" that switching from a regular fan to an e-fan nets you 5-10% more HP and fuel economy. Which is pretty significant. BUT...

So a fan thats connected to the motor gets spun directly by the motor. But to spin an e-fan, you have to turn some of that engine power into electricity, then turn that electricity back into movement. So logically, e-fan's should be noticeably LESS efficient than direct drive fans, because neither alternators new electric motors are 100% efficient.

So where does the power gain come from?


Then on to more specific questions, I've read not so great things, including just the other day, about using efans in these trucks. What's the story there? And like always, does general information that mostly comes from 4.2 land apply to my 5.3? Even if the gain was just at the low end, 5% more HP and 5% better fuel economy, that's still pretty good.

 

[Mooseman]

5-10% more HP? On a 300hp motor, 15-30 hp? Nope. This Tahoe picked up 9 hp.

There was another video I had seen years ago where they did the same on a Dodge truck, That was just 2-3 hp.

The radiator is basically the same between the I6 and V8 with the only difference being the lower hose outlet position. Like I said in your build thread, they cheaped out on the radiator.

Oh and A/C performance is absolutely horrendous when idling.

 

[Blckshdw]

I tried this experiment and it lasted 1 weekend. Got a PCM of NC I6 fan shroud, got one of the strongest 16" Spal fans I could get. (since their kit comes with a 16" fan) A variable speed fan controller with AC trigger input. Also took the extra step to seal the 2 sides of the shroud with foam tape to ensure full air passage over the radiator.

It was May here in FL, and I went for some leisurely drives with the windows down. The temps climbed steadily as they typically did, but when I stopped at traffic lights, the temps would continue to tick up, when before they would at most hold steady. I had also wired in a manual switch so I could command them full speed when desired, and the best they could do was hold the temps where they were. There was ZERO cooling action at a standstill. I'd get more cooling once I got moving.

Seemed pretty clear, if this is how well it worked in May before I considered it too hot, July and August would probably be a major problem. Next day I took everything out and went back to stock. Didn't even have the time to post pics of what I had done... MAYBE going with dual 12" fans would have performed better, but I don't imagine by very much. Also the fan was loud as hell at full speed.

I do know some who've made efans work, but an aftermarket 3 row radiator, and a modded mounting method was required.

 

[azswiss]

So where does the power gain come from?

The electric fan draws power from the battery as well as the drive belt (via the alternator) versus a mechanical fan getting power only from the drive belt. Although there are efficiency losses in both the alternator and the electric fan motor the instantaneous load on the belt is going to be lower. There is also less inertial & drag loading from the spinning fan blades. Finally, the battery is charging all the time so any mechanical power draw is spread out over time versus when max power is being requested. The net result is that when you stomp on it there is more "apparent" power that can be applied to accelerating the vehicle.