Hey guys I want to know if anyone has ideas on how to calculate cfm needs for an Electric Fan. I am running a new 2 copper core radiator on my 71 Demon with 340 and now have a Pro-Comp 16 inch fan that is supposed to move 2500 cfm. Does great driving down the road but stop at 2 lights and its up to 220 and climbing! I've been looking at the Perma-Cool unit that moves 2950 cfm as my cousin has one that he feels is moving nearly twice as much as mine plus the Perma-Cool unit has aluminum fan blades. Any help would be greatly appreciated! Maybe some one has an Electric Fan on their A- Body?

Werty, Is it set up as a pusher or a puller? 2500 cfm, should be more then adaquete for your set up.


If you have it as a pusher I would suggest setting up as a puller, them add a shroud.

JMO

Mike

Your fan should be adequate or at least nearly adequate if it is set up as a puller. A shroud would help as well to direct the airflow.

If your engine is raising by 30 or 40 degrees just from stopping at two lights, then I think you may have something else that's causing the motor to run hot. Maybe timing or mixture?

I am assuming the WP is in good shape but might be something to check. Maybe pinch the hoses (wear gloves) and see if you feel the water flowing?

I have a set of dual 11's on my Charger rated at 2670 CFM together and they cool my BB stroker motor all day at 180-190 degrees....even sitting idling on a hot day...

There is no calculation for cfm. It depends on too many things such as blade design, shroud, grille, physical motor size, etc.
If you're going to use electric fans they MUST pull some amperage. If the motor isn't pulling power it isn't moving air.
The fans you find at the parts house are good for supplemental cooling but should not be relied on for primary cooling.
How many of those cheap crappy things do you see factory installed in cars?
NONE!

If you have the room, go with a Mercedes fan upgrade on a 26" radiator. It's been discussed here at great length.

If you don't have room for that or are using a smaller radiator, go back to the factory shroud and thermal fan clutch.

I believe you need 5000+CFM if used for primary cooling. Aftermarket with that capacity is quite expensive so OE, either JY or new replacement is preffered. Replacement Chevy HHR fans aren't too expensive, Taurus fans are supposed to be good. There's a guy who likes Mercedes also.

The reason some of us like the Mercedes fan is the volume of air it moves. It's almost disturbing. The HHR and Taurus fans are puny by comparison.
Yes, it's more expensive but if you use it there should never be another problem with air flow.

I plan on going to the Mercedes fan route, but I think I will need to go to the Denso alternator first.

If you run hooziewhatsit's controller you'll be fine with a 78 amp square back alternator. That really cuts down on the fan's electrical consumption. There should be very few times when it's running at 39 amps. The lower speeds draw far less amperage and will cool most cars even with A/C running.


One thing I should have elaborated more on earlier is the cfm rating of fans.
There is no industry standard on cfm ratings. Manufacturers will run their fans with a perfect electric feed and with no restrictions in the way. That results in a perfect world rating.
In the real world, there's a radiator in the way and a less than perfect electric feed. The fan will have to work harder to reach it's maximum speed and maximum air flow. If there's not enough motor, there's not enough air flow. having enough motor means you will be pulling a minimum of 30 amps to get the fan running. If your fan suggested a 20 amp fuse it's not going to move much air. Another way to tell is if the fan has a 10 gauge or smaller wire on it. 12 gauge wire will get hot running a continuous 20 amps. A typical 10 gauge wire will get hot running 30 amps.

I agree with the others; something else is not right. I have a 1600 cfm (too small) fan on my 69 Road Runner with a 470 stroker and a MP water pump and my car does not go over 205 in traffic and stays around 190-195 most of the time. My car was also getting hot when I first got the motor together but little by little it started running cooler when I started tuning the carb for more fuel and got the timing set. When I adjusted the floats and idle mixture screws on my carb it was a night and day difference. My car was way lean when I first fired it and drove it for the first few times; my timing was retarded enough too that the headers were glowing red after about 5 minutes when we first fired it up. I would suggest adjusting your idle mixture screws using a vacuum gauge first and see if your getting enough fuel; check the timing too. I would start checking everything else from there; it can get a whole lot better. I ended up going way up on pump squirter size and jetting after that and it just kept running better and at lower temps.