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electric cooling fans - brands and theory


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Does anyone have any particular preferences for electric cooling fans?

 

I'm using a Griffin aluminum 2-core radiator, 27 1/2" by 19" (it fits when angled forward, and when the stock Datsun sheet metal crossmember connecting the inner fender is cut out), and I'm trying to cool a 350 hp 454" big block. With the angled radiator, a pulley-driven fan is not practical.

 

Also, I'm sure that people have noticed the claims that while pulley driven fans may absorb on the order of 10 hp, electric fans supposedly draw less than 1 hp max (1 hp at 12 volts = ~60 amps!). Granted, the blades of electric fans are more efficient, electric motors are about twice more efficient than internal combustion engines, and there are fewer parasitic losses (rotational inertia of fan clutch, friction of pulley belt, etc.). But we're talking orders of magnitude here! I just don't see how the numbers stack up. Any ideas???

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I tried to use my two 10" hayden electric fans with a thermostatic switch on my Griffen 19X26 radiator and had to use a 6 blade semi flex fan instead. I'm not to sure how much HP you will lose, but that extra HP will do you no good when the radiator is belching fluid!

 

Mike

 

------------------

 

"I will not be a spectator in the sport of life!"

mjk

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Guest Anonymous

I've got a couple comments. First of all...you are just begging for a serious problem if you cut out any crossmembers and didn't replace it with anything. You are running a serious motor in there and should NOT be cutting out pieces to make a radiator fit. The reverse should be happenning...you better be adding some serious structural add-ons that you didn't mention or I would not even step in that car unless you have a death wish. The datsun unibody has enough problems keeping straight when left in its entireity.

comment #2. The radiator needs to be in perpendicular contact with incoming airflow. Your radiator is acting like a wall right now and not letting much of that air through. I'd bet you notice some pretty bad buffetting at highway speeds due to the giant bug scoop you have created. Do yourself a favor and ditch that radiator. Put the crossmember back in and get a good 4 core unit that fits right. You are running too big a motor to be running a 2 cored radiator. Your fan has nothing to do with it. You could put a 10000000kw fan that is 300% efficient in there and you would have the same problem(well..not really, but you get my point). Please fix these things before you kill yourself in this car and/or melt the engine into a single metallic blob.

 

SpencZ

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SpencZ,

 

Well, first of all, this car is still under construction, so it will be a while before I actually kill myself. :-) Second, it's a full tube car, with what amounts to a GT2 roll cage and extensive reinforcements beyond those required by the various race sanctioning bodies, and well beyond those described by JTR. The assembly is currently on a chassis jig, custom built just for this car. There is not much loading ahead of the strut towers. Funny cars, trans-am cars, and many others don't have any structure ahead of the strut towers (except for a lower bar to tie together the left and right side frame ends), other than some mounting mount for the nose clip.

I'll have some photos next week - I keep promising, but slides are difficult to get scanned.

 

Third, I've done a little bit of tooling around with air flow issues. In fact, I probably would not be making a bogus claim to say that I'm the only person on this list that has actually done laboratory testing on the flowfield over the Datsun Z. Granted, lab is not real life, especially with the so-called Reynolds number affects that govern things like flow separation and boundary layer stability. But, it's a start.

 

Angling the radiator to accept oncoming flow upstream of the air dam is a usual practice, albeit not with Z's. Also, with the stock Z hood lip geometry, flow above the grill-area stagnation streamline will separate, causing a serious loss in stagnation (total) pressure. The part of the fan behind the hood lip area is getting nothing but some minor eddy flow from the local upstream shear layer instability ("Kelvin-Helmholz"). And with the angled fan, ejecting the flow exiting the radiator cores (you do have to conserve mass, after all) is more efficient, given the location of the engine.

 

Two-core vs. 4-core is a moot comparison without actually considering the effective convective heat transfer coefficient. That is due to a number of factors, such as the tube shape and diameter, tube head losses, fin density, air flow losses across the fins, etc. The downstream cores of a 4-core radiator are much less efficient than the upstream cores. Thus, more is not always better.

 

The reason for using electric fans is NOT to eek out the last big of hp, but to build a more mechanically practical assembly. My motor is 6" further aft of the JTR setup, and the ducting to use an engine-driven fan would just not be practical. My question regarding electric fan efficiency was asked to learn 1) whether folks that have switched from engine-driven to electric fans really did notice an increase in hp and torque, and 2) to find out how advertised fan CFM rating compare with what people have found to be sufficient to cool their engines.

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Guest Anonymous

...So now everybody knows that you know what you're talking about. Why didn't you just clarify your question in the beginning so you didn't sound like a moron with a flimsy overheating death trap?? I guess you were waiting to trap somebody like me who hates dealing with Reynolds numbers and coefficients of frictions so you could sound like the smart $h!t. Anyway...sounds like a good project you have going. I'll agree with everything you decided to share with me on your project after I go back into my fluids and thermodynamics texts for refrence....next time give the whole scoop before asking any questions. It will help my ego recover and maybe encourage me to keep my mouth shut.

 

SpencZ

Going to bed before I start any more trounle...

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Lets keep it civil guys, there is no need to try to out-do one another. We are here to help each other out. Pete,Mike i hope i am not stepping on your toes here.

 

As for the fan issue here. I have a 475 hp

sbc and a 16" autozone special electric

unit. I do not know the flow #'s on this fan but it draws max 13 amps. I have 350 miles on the car and have had NO (0) problems with cooling. I am using the factory datsun radiator, and the car has NO air conditioner parts

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SpencZ,

First, lets all tone down a bit on the posts. I think Michael assumed that others had read enough of his posts and knew that he is A: smarter than the average bear, and B: a freaking rocket scientist. Anyway, no harm, no foul.

 

Now on to my reply to the cooling issue:

JTR makes a few claims about aluminum radiators that aren't true. Aluminum does require flushing more often, but it isn't a big deal, because you should flush your system once per year anyway. Also, aluminum radiators are MUCH more efficient in general, same reason aluminum heads are prefered.

 

Now, 2 core Vs. 4 core: This is a huge misconception. "Core" means nothing. What you should be concerned with is the diameter of the tubes. My griffen radiator is 19X26 and has 1inch tubes running thru it. It is BY FAR more efficient than the nice little 4 core unit I used to use. Always check to see what the size of the tubing in the Core is before you buy off on a 4core unit.

 

Michael, You seem to have this project well in hand. What is your target time/speed in the 1/4? Sounds healthy. How hard was it to cut and move the firewall?

 

Mike

 

------------------

 

"I will not be a spectator in the sport of life!"

mjk

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  • 8 years later...

I'm running the 19X26 Griffin Aluminum with 1" tubes and a Flexalite Black Magic fan (~2600CFM). 355 SBC, 11:1 CR, Performer RPM heads, Comp XE286H cam, 2.25" dual exh, stock body. I run a 180 degree thermostat and the temp gauge hardly ever moves beyond 187 degrees. It did climb to 195 one time last summer in Atlanta gridlock after 2hrs at 95 degrees outside temp. I've been running it like that (daily driver) for three years. The aluminum radiator holds up very well under daily driving.

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Wow, this thread certainly brings back the memories! 8 years ago I was less humble, though on balance at present I have far more cause for humility.

 

For what it’s worth, I too have a Flex-a-lite “Black Magicâ€, model 150. By now this has become a standard solution. It works tolerably well, even in hot weather, provided that the water pump is spinning (which it occasionally fails to do, for example upon throwing the fan belt; once in a rather awkward heavy-traffic scenario such an incident caused a temperature spike to 240 degrees). By now the front end of my Z is considerably revised from stock; the stock hood-lip problem has been solved – functionally, if not cosmetically.

 

What has not been solved is the thorny problem of lack of basic mechanic’s acumen for engine maintenance and tuning. A fellow on this board, whose car budget is less than the roundoff error of my budget, and whose Z now accompanies mine in the garage, went from headless shortblock to fully-running car in a matter of a few wrenching sessions over two weeks, and then proceeded to drive 1200 miles round trip to a drag race without major qualm or incident. 8 years ago I would have thought that I could have accomplished a similar thing. Today I know better than to even attempt it!

 

Sorry to hijack this thread (my own thread???) with sappy reminiscences, but it truly is disconcerting how little actual progress has been made in 8 years!

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