How much horsepower would I gain by using a 18" electric fan on my 390FE! I'm kinda tossing this one around. Thanks.

 

Save your money.
I'm betting good Food on this answer..... NONE!

If you dont have access to a dyno, you can proove it this way.

Find a steep hill. With good traction surface, on a good clear winter day. (The local baromerter at 29.95 is your truck's best performance day)
Do about three runs up this hill from a starting place to an ending place and time it carefully. You'll need a friend with a stop watch.
This run only needs to be a hundred yards or so.

Then take the fan blades off your truck and repeat the exact same test.
The stopwatch will tell the tale. No blades similates the electric fan installation.
Be sure and let the engine cool down between runs.

Torque is the twisting force it takes to power the truck up the hill.
Horsepower is the 'Speed' or 'Time' it takes to develop that horsepower.

I'm betting there is no discernable difference. And if I'm wrong, tell us about it.

 

Don't forget the drag on the motor when the fan comes on and the alternator has to make up the difference.

Ever notice how the idle drops for a second when an electric fan comes on?

art k.

 

The manufacturers do caim HP gains of 10 or so HP. They may not be verifiable, but I do like the idea of the fan spinning a full speed regardless of engine speed. Sitting on IH35, stuck in traffic in the Summer Texas heat, one can appreciate the higher air flow at idle.

I'm considering an electric fan. let me know what you find out.

 

I like the idea of an electric fan. They will increase power (the tradeoff between alternator drag and powering a mechanical fan is significant) but not enough to make it a good reason to upgrade. I agree with Gtex here. A fan running full blast at idle where it actually needs it is the way to go. You get very little flow from a mechanical fan at a stoplight where flow is the most critical. If your truck was always moving 60 MPH you wouldn't even need a fan. I plan on adding one to my truck. It will be thermostatically (real word?) controlled. That is how these newer cars are getting away with heater core sized radiators. I take one statement back. I will probably wire the fan to a switch in the cab. I trust my finger more than an automatic switch.

 

You should see some gain. Dont know if it will be noticeable or not, but it all adds up. Oh and ratsmoker, dont forget to flip the switch! I'd have both the regular switch and the thermostatically controlled switch and hook them up in paralell.

 

I like the electric fan idea. I will probably do that eventually. I think one thing the naysayers are forgetting is how much drag there is every where a v-belt goes around a pulley. If those things didn't suck so much HP, the auto manufacturers wouldn't have gone to the trouble to change over to serpentine belts.

 

To th original question: about 5 - 10 hp. Is it worth swapping just for power? Not unless you are running a full on drag truck. The drag you lose is fairly significant compared to the extra drag on the Alt. The idle benefit is signifcant as well. I think if HP alone is your only motivator then no it isn't worth the change. Throw in all the other +'s then it makes it some what worth the it. I know when mine goes back together it will have an electric rad fan. Of course it will be mainly used to race with.


Scotty

 

So, what size and CFM rating would you (or do you) use? I've been looking through lots of catalogs and the specs are all over the place. Does anyone know how much air the stock fan pulls at idle?

I'm seriously considering this mod too, so if there is anyone out there who has done it please let us know the specifics.

Mark

 

I didnt read but 4 or 5 of the posts, but Im gonna reply anyways.
Electric fans may not make you "pick up" a whole lotta horsepower but they are very nice. I run the stock fan and electric on my GMC and on my 390 FE I just run a electric fan w/ a thermostat on it so it kicks on at a certain degree. You can pick up those for a few dollars out of catalogs.
I have it set kinda low tho, just in case. I have it set at 150 degrees. It seems to stay pretty cool

 

OK, so if someone does a lot of idling, short moves, loading, unloading, city traffic, heavy-slow traffic, and maybe all with the A/C on, you would truly appreciate the benefits of a thermostatically controlled (w/manual bypass) cooling fan.
I'm sold! Where's this reasonable fan at? What catalogue?
My '73 390 has always ran a little warm in the hay field, even when it had a 360.
Thanks, s

 

I lucked out and got a fan off of a Ford something or other car. it was a 99.
I found the radiator and fan on the side of the road.
I got it and it fit rit on my radiator on the 390 and it worked!
Didnt have to make any brackets or anything, pretty much fit right on.
Fans can be found anywhere, parts stores, summit, jegs, etc.
The thermostat is fairly cheap and can be found at the same places.

 

One place that I have noticed that a electric fan is a must is on my 4 cylinder turbo charged car I will not say what brand for it is not a Ford. Nevertheless it is thermostatically controlled, and when I run the car hard the fan runs continously, even after I turn the car off, it would continue to run. I have noticed with larger V8 motors that when you run them hard and turn off the engine, the engine gets hot (noticed if you have a mechanical gauge), because the hot water rises, then when you go to start it back up, a few minutes later the carb is hot, the fuel is hot, and does not want to start. I think that a electric fan that runs even after the car is turned off is a great idea, HP gain or not, it's just money right guys.

 

I've been given a pair of 15" fans from a car that I'm thinking about hooking up in my truck. Unfortunately, I'll have to fabricate a bracket and some wiring. Summit sells a thermostatically (yes ratsmoker, *I* think it's a word) controlled relay for switching the fans, and I'd prefer to hook it to a key-on circuit rather than a manual switch in the truck.

I imagine that these two fans pull quite a lot of current; however, I believe that I've got the small 38 amp alternator. Any ideas where I should wire these things in, or if my alternator even will support these? I've got that '73 donor and it has a larger alternator, and I suppose that the regulator will go into my truck. But I haven't looked yet.

 

Wire it up on the starter solenoid
That way it comes on/off with the key
Easiest way I think, and alot less wire than running it inside the cab