fishslayer143

You misunderstand the way a clutch fan works.. it turns MOST at low RPM and very little at hiway speed ..a standard clutch slips, and may only turn 30% of engine rpm at 2500 rpm. even a thermal clutch works the same except if air temp coming thru radiator reaches its temp setting, it engages the clutch at higher percentage of engine rpm . A mechanical fan moves more CFM , than electrics, also can move more air by just increasing engine speed.. An electric cannot .

pauldana

You know that’s similar in some ways to the brushless fan the speed is regulated by the computer at highway speed’s when there’s a lot of airflow going through the radiator if it’s enough to turn the fan blades then there’s no power to be used
Or just enough power to turn at that pre-Determined RPM
aloso you can have ramped starts and stops, as well as programmable lowers speeds for cold weather aplacations
cant do that with a standard brushed fan

Bikespace

I'll stick to the twin 11" brushed Spal's for now. Their website says 30 to 40 Amps, depending on airflow, for the pair of them, which is a bit more than I measured. Also, they come with a shroud, so you don't need to fabricate one out of a cookie sheet. Thanks for the info on the brushless options!

pauldana

not a problem... BTW. Delta PAG also make custom shrouds..

pd

DorianC3

I must say... you gents (and the lady who also answered) are fantastic ! Soooo much information here to chew on.

A follow up - I used to have a 200 Amp alternator feeding a variety of circuits. With a base model 1969, I would presume that the OEM alt (in good shape) would be enough to feed twin fans.

Has anyone kept the OEM Alt ?

Bikespace

I have a 150A 12si alternator, which replaced the OEM one when that one couldn't keep up with my stock high beams. Figure 30 A just for the fans, full blast, when running. It would work if you do a lot of highway driving, but as soon as you hit traffic, you may be in trouble, especially at night.

carriljc

I have a Lincoln Mark VIII fan that I actually bought new and have been using for about 15 years. It's been great but they're not made anymore. Don't just go buy any so-called Mark-8 fan on ebay. Most of the crap you see will be T-bird or other Fords being called Mark 8 fans. Real Mark 8 fans are single speed. You can search and verify that info this website if you so desire.

ANYWAY, my Mark 8 fan has been wonderful, but if I was to do it today I would get a dual fan setup from a ~ 3.8L camaro. It is a pair of fans so you won't have the single failure concerns of a single fan. You can order these new also. Here is some info I found for these guys...follow this link:

https://www.corvetteforum.com/forums/c3-general/3527451-project-serpentine-belt-conversion-sbc-4.html#post1587817315

FYI: I had to upgrade my Alternator to a 140 amp CS-144 to support running this fan along with A/C, EFI, and associated electric fuel pump.

Bloodzone

Thanks for the education. I was thinking engine RPM had more of an effect on fan speed.

lionelhutz

I'm quite skeptical of the Delta PAG numbers. Directly according to their website;

"Brushed DC motors have a typical efficiency of 70-75%, while a brushless DC motor can achieve 96% efficiency, a +28% improvement."

So, they are saying that a brushless motor could be 28% more efficient, not that they are 28% more efficient. Marketing BS at it's finest. Data I've seen from other manufacturers of both types of motors put this number in the 10-20% range.

Then, their Watts/CFM used will calculate out to be over 2X that of a similarly sized brushed fan. How does a motor that could be 28% more efficient make the fan use less than 50% power to flow the same CFM? From the data posted here;
16" fan - 80W/1000CFM vs 186W/1000CFM - 43% power in for the same CFM out. This does not compute when comparing motor efficiencies.

I've have seen people post claims that they have a much more efficient blade somehow. But, that just implies that the brush type fan manufacturers haven't bothered designing their fans for best efficiency, which seem rather dubious.

On another note, sure a brushless fan motor by itself will be more reliable than a brushed motor since it has no brushes to wear. BUT, the electronic controller it requires can easily cause it to lose that reliability edge.



No, the stock base model alternator will not work, no matter what type of fan or how efficient they are.

Stock type 10SI alternators might only produce 20-30A at idle, which is barely enough to keep up with the lights at night. A hot-rodded 105A 10SI alternator might only get to the 30-40A range at idle which is still not enough for a fan or fans at night with everything else running. Be careful what you buy and definitely check what the idle amperage rating will be.

htown81vette

If your radiator is good enough having an electric fan failure is not even on my list of things to worry about. I drove my Corvette around everyday for months, and even through the summer months, 100+ deg temps before I realized that I had unplugged the electric fan (to do something else) and it wasn't even working! The ONLY reason I found out is I had it idling in a friends driveway for like 15 minutes before it started to overheat. LOL!

Gordonm

Not really. The stock non AC cars used about a 42 amp alternator. With twin fans pulling a lot of amps that will consume most of the alternators output. Now if you have headlights on and radio and running the car there is no power left over for them. Even the Ac alternator at 63 amps is marginal and if you are running the AC no way. There are upgrade kits for the stock alternators to about 80 amps. I did this to mine before I went to the LS alternator and it supplied plenty of power.

carriljc

I had a GM 12si 94 amp alternator installed and while it does well while at speed, it could not maintain voltage at idle. I now have a 140 amp CS-144 and it does just fine. You can search this forum for conversion pointers.

DorianC3

I am seeing a lot of numbers here on Amps...

What about CFM? What total CFM (sum of 2 fans?) is required to cool let's say a 400HP, 383 ? Assuming an aluminum radiator.

DorianC3

Incidentally, from what I am reading - it seems clear that step one is swapping in an aluminum radiator.

Jebbysan

My take on electric fans is different.....they work better yes but on am on the fence right now for a strictly aesthetic reason......
I spent a lot of money and time cleaning and powdercoating/painting the factory fan/clutch assembly.....and it works great....but DAMN is that thing heavy......I think it is like 12-13 pounds hanging of the shaft of the water pump.....which to me isn't cool from a racers standpoint....my engine spins up FAST and I don't like the physics going on there related to the clutch....but it looks like it is supposed to be there and the shroud is mint as well. I want an electric fan but want to leave the factory shroud in which looks kind of stupid.
My idea is to come up with an electric fan that fits in the 'halo' of the shroud.....this would do the exact same thing as the factory salad cutter.
And on the aluminum radiator tip....they work great too but my factory Harrison A/C style rad functions perfectly and cools my .030 over 406 in Texas just fine......so there is that as well.

Has anyone here thought of or has put a fan in the original shroud?

Jebby

Bikespace

Too many variables! Your best bet is to get data from people in your situation. For example:

On a 90 degree day, such and such engine and radiator, 30 minutes in stop and go traffic, electric fan turned on and off (full power) with a 50% duty cycle, voltage constant at 13.7 VDC.

With a report like that, zero margin, and all else being equal, you could possibly get away with 1/2 the CFMs of whatever was used in my made up example, though your alternator would need to be able to handle the fan running at 100%.

The links above should have the CFM ratings of the fans.

REELAV8R

i think the problem you may run into Jebby is finding an electric fan motor strong enough to be able to run a single fan that could produce as much air as your mechanical fan.
The mechanical fan can have it’s blades at a higher angle of attack and have much longer chords on each fan blade to Move LOTS of air. After all it’s being turned by the water pump who’s only limit is the belt(s) driving it.
An electric fan is going to be more limited in this regard, by size and amperage available, at least when you limit the diameter to one that will fit in your current shroud.
it would work I suppose but move less air. Without A/C and if it wasn’t too hot or humid outside it would probably keep up fine.

REELAV8R

i am using a set of these fans.

https://www.ebay.com/itm/Dual-11-Ele...YAAOSwm9tZvChR

i have them behind a Dewitt’s radiator and use a 110 amp 10si alternator. It keeps my 77 with A/C , th350 trans ( so more heat to dissipate) and 440 HP cool even on 100* days. Now our humidity is not high, maybe 30 percent, and that helps.

all electrical needs are met with the 10si. Been that way for 8 years now.

i would say a good aluminum radiator is a must.

Jebbysan

I thought this myself....I would have to look and see what is available....the shroud is too nice to remove!

Jebby

REELAV8R

just had a though on this....

what if if you put two electric fans in a series type arrangement? One in front of the radiator blowing through it and a second one in your shroud behind the radiator.

in this way the second fan would have to suck less and be provided with essentially a “head” pressure from the first fan making the second fan more efficient, particularly at low vehicle speeds where heating up would be a bigger problem.

wild card would be the available space to install a fan on the front of the radiator. Without A/C it should be doable.