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Discussion Starter #1
I am tossing a big arsed aluminum rad in the 67 and thought this would be a good time to think about the cooling system as a whole. I have an external trans cooler waiting to bolt on and now I'm looking at the fan and was hoping to get some input from folks smarter than myself.

Although I don't want this to be all about my engine as I am looking for some general guiding principles in cooling rather than specifics for me but I am running a mild 351W today with approx 300 horse. I will be building the 408 next year once I get the rest of the car done and on the road which should be pushing a little over 400 horse and 400 ft lbs. (Still needs paint and headliner.)

I have an Oil cooler I could run on the car for cooling but for a 400-450 HP target I think that's a bit extreme and just another failpoint on the vehicle.

So back to the Fan question... Has anyone done a lot of research on the merits and drawbacks of mechanical vs electric cooling fans? My own brief bit of research and just logic would indicate the electrics would be far more efficient simply due to their proximity to the rad vs the engine fan which is a couple inches back.. Combine that perceived cooling benefit with the fact that, however small, there will be a slight engine stress relief/HP gain by removing the mechanical fan blades and it seems like a win win.

Anyone got any thoughts, experiences or feedback?

Thank you all kindly.

Mark
 

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our 67 big block a/c ran right on the peg last summer in 117 deg in laughlin nev---every thing held it's own until i got off the highway and caught a 3 minute light---then she puked!!---i came home and immediately put in an alum radiator but still with the stock shroud/fan set up---and i got no difference in operating temp and still had the getting hot when you got off the highway---basicly a lack of airflow
i then got the 140 amp alternator , the spal 11" dual fan setup/shroud , and spals pwm/computer fan control---i had to add an idler pulley under the a/c compressor for belt to fan motor clearence--but it finally all went in---i used a later model 390 thermostat housing that has provision for another temp sender--i started off with the optional sender offered by spal---could't get the sys to operate correctly--i talked to spal tech and finally got out of them the fact that they tried to copy a chrysler sender---i bought a real chrysler sender and things improve greatly but not perfect---after many calls to spal tech and a bunch of unprintable words , one of the tech guys mentioned the word "ground" . i was using chassis ground as directed but ran a 6 ga wire from the bat neg terminal to my chassis ground lug---now everthing works as planned/designed---absolutely no temp over 200 deg and with the a/c on (both fans on full) the car will idle @ thermostat temp with 95 deg outsde temp---this is the same fan setup as shown by azcat and he should know about temp
i wish i wasn't in such a hurry to fix colleens car as i think the dual electrick fans might have worked just as well with the 4 core copper radiator as with the 2 row alum rad---if you think about it , all the new cars run @ 22+ deg and all have electric fans
doctordesoto


i have a 26" , 4 core copper big block (1968 bottom tank) with about 3000 miles on it if anyone is interested
 

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If you believe that the laws of physics are more than just suggestions...

More horse power equals more heat. Your stock cooling system may need to be upgraded. Most over heating is caused by mechanical issues: incorrect timing, wrong mixture, etc.

Brass conducts heat better than aluminum, but is much heavier. There is not inherent advantage to aluminum other than weight.

Once your car is moving, the fan is not needed. Calculate the cross sectional area of the radiator opening, and then multiply this by the number of feet you move per minute and you will get the air flow in CFM. For example a 24" by 18" opening is 3 square feet. At 30 miles per hour you move forward 2640 feet per minute, so 3 x 2640 is 7920 CFM. A Spal dual 12" fan will only move about half that much, most even less than that.

If your car overheats on the highway, the problem is water circulation mostly clogged radiators. If your car overheats only at a light, the problem is airflow. The easy fix is to increase the idle rpm. If your car overheats all the time, then the radiator is too small or extremely clogged up.

A fan shroud is critical. The fan should be 1/2 way and 1/2 way out of the edge of the shroud. The distance from the radiator is not critical to the performance of the fan, but it is critical if you have a thermal clutch. The clutch needs to be the right distance (depends on the clutch) from the radiator to properly sense the temp of the radiator core.

The clutch on a mechanical fan is a wonderful thing. It limits the top rotational speed of the blade. Fan blades are designed to work at a specific maximum rpm, spinning it faster actually reduces the amount of air it will move. A fan clutch allows the pitch of the fan to be more aggressive and therefore effective at lower RPMs. It also keeps the fan blade from coming apart due to centripetal force.

Some electrical fans use shrouds that only cover about 65% of the radiator,look for ones that cover at least 85% of the core. a factory shroud will cover more, close to 100%. Puller fans work by creating a low pressure area inside the shroud.

More cores is good, and more fin area is even better. The concept of moving the water too fast for it to cool off is a myth. What is important is the relative temperature difference of the water, the fins, and the air.
 

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Oh, and it takes MORE power to run an electric fan than a mechanical fan, due to inefficiencies. The amount of horse power it takes to move the air is the same no matter whether the motor doing is powered by electricity or hamsters. It is a lot easier for the hamsters to drive the fan, without putting an alternator and an electric motor in between them and the fan blade. Converting mechanical energy, into electrical energy results in a loss of efficiency (driving the alternator). Converting electrical energy into mechanical energy (motor driving fan blade) also results in inefficiency. Modern cars use electrical fans for many reasons, mostly due to packaging (front wheel drive with transverse engine mounting), air conditioning, and low rpm cooling issues. When coupled with a computer, electric fans can be very highly tuned to make them only run when needed, including after the engine has shut down.
 

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xr7g428---your right about the cfm going down the road and also right about the computer---thats why i went with the spal pwm computer system for my wifes car--unless the a/c is on , the fans don't run going down the road and as you know a big block early cougar with a/c can be a pain while idling for any length of time , especially with a heat soaked engine running across the desert--the spal fan shrout covers 100% of the rad and has 10 ea 2x3 rubber flap doors that blow open at speed to keep the air flow from being trapped in the fan shroud .many people would probably just put a toggel switch on the fan but i believe in making my wifes car as failsafe as possoble witout looking like a new car--without the a/c on , th pwm system starts the one fan at about 1/2 speed just above thermostat tem---as the temp rises , the fan speeds up to increase air flow---when it gets to about 200 deg(if it does) ( a temp i programed into the computer) the second fan comes on full---dropping the temp down to about 185 --then the # 2 goes off and the # 1 fan drops to about 1/2 speed--all i know is the swstem works very well and very well all by it self--the cost and effort is worth every cent when colleen takes off in her car
i think this is also why she never *****es about whats being spent on any of the car projects
doctordesoto
 

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Discussion Starter #6
Hey guys, thanks for weighing in.

Bill I am not sure I understand the bits in your last post. You say it takes more power to run the electric fans due to inefficiencies but that extra electrical comes at the advantage of less stress on the engine and freeing up a few ponies by not having the mechanical fan try and push the air around the block.

I am by no means an expert on electrical systems so please enlighten me if there is some basic underlying principle I am missing. Sure the electrical system has to have additional load to run electrical fans, but the whole reason for moving from mechanical to electrical is that you take the power requirements for moving the air off of the engine and transfer it to the electic fans. On our cars electrical systems the alternator is running constantly to power the charging system. Adding more fans to the load of the charging system has no bearing on the actual power it takes the engine to turn the belt on the alternator.. it is engaged constantly all the time. the regulator is what controls wether the power is used by the charging system or not.

So with the whole concept of removing unnecessary power robbing airflow movement from the engine an dputting it on the charging system which is running regardless of whether or not you have a use for it... I just dont see the argument that electrical fans rob more power from your engine.

Maybe I misunderstood you though.


Thanks for the input.
 

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Not sure about taking more power, but they do take power. An alternator will put out enough power to keep the system charged, but when you throw a big draw on the system with 30 amps worth of fans, it makes the alternator work harder. I have 2 electric fans on mine that are set to come on at around 170° and when they do kick on, the idle will drop because of the extra strain on the alternator.
 

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Discussion Starter #8
The idle may drop Mike but how could it be from extra "Strain" on the alternator? The alternator is simply an electric motor that generates current by spinning the wound copper spools around the magnets. It generates the same amount of amperage regardless of what the load is and the regulator determines where that amperage goes.

I'm going to do more research but it would be a real shock to me to find out that the alternator takes more energy to turn based on the "load".

Great to have this discussion guys. I'm hoping someone can teach me something as dense as I am ;)
 

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What you are missing is the basic physics of the process. To move a given amount of air requires a specific amount of energy. You can rotate a fan blade with an electric motor, or a gasoline powered motor, or a hamster powered motor, it doesn't matter the energy source, the amount of work is exactly the same.

All of the energy available in your car comes from the gasoline engine. It basically converts the heat energy of burning fuel into mechanical energy in the rotation of the crankshaft. You can convert some of that mechanical energy into electrical energy by spinning the alternator, and then convert the electrical energy back into mechanical energy by feeding the electrical energy into an electric motor. Every time you make a conversion from one type of energy to another, some part of the energy is lost in he process, primarily in the form of heat.

There are several misconceptions that need to be cleared up. First off, the cars electrical system, when running is powered by the alternator. The alternator has to do two things, recharge the battery, and to provide enough power to run all of the electrical devices of the car. The alternator output is not constant. The output of the alternator is controlled by the voltage regulator. One way to measure power is in watts. One horse power is approximately equal to 750 watts. Watts are equal to current, measured in amps, times voltage, measured in volts. So if you have an alternator rated at 100 amps, at 14.4 volts, it can produce 1,440 watts, or about two horsepower of energy. Since the conversion from mechanical energy to electrical is not perfectly efficient, it will take more than 2 horse power, (probably approaching double), to make that much electricity. The more output the alternator is asked to produce, the harder it is to turn it.

If a gasoline engine could spin an alternator and make more power than the gasoline engine, we would have an unlimited amount of energy and also a perpetual motion machine. Both of which are mot physically possible.
 

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So to compensate you put in a higher capacity alternator?
 

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Discussion Starter #12
Thanks for the update Bill. I'm probably just being obtuese but all my research is simply pointing to the electrical fans being exponentially more efficient. Doesn\t mean it's right but this thread : http://www.twoguysgarage.com/forum/showthread.php?t=9647 has a guy "saltmine" who used to work at GM testing cars on the chasis dyno. Here's his thoughts:

First, when I worked for GM, we discovered, on a chassis dyno, that a mechanical fan can draw up to 26 horsepower. Usually something like a seven bladed fan on a clutch, that is...Once the clutch engaged, the hp dropped sometimes as much as 26 hp.

Interesting stuff when you consider that at the worst an electrical fans load will draw only 1.5 to 2 HP tops. He makes the pretty telling argument that nearly every vehicle produced in the last 15 years has electrical fans and not mechanical.

Still more research to do for me but Im leaning electrical.
 

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Every time you make a conversion from one type of energy to another, some part of the energy is lost in he process, primarily in the form of heat.
All of this talk about conversions makes me think about diesel-electric power-trains used to propel cars, trains, and ships...
 

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All of this talk about conversions makes me think about diesel-electric power-trains used to propel cars, trains, and ships...

Shhh - you need to call them hybrids.

The way forward with vehicles appears to be electric power with a gasoline engine driving a big alternator to charge the batteries
 

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All of this talk about conversions makes me think about diesel-electric powertrains used to propel cars, trains, and ships...
However, when you're talking about trains and ships, those configurations are using the diesel-electric conversion as a transmission to propel the vehicle. In an automobile, a mechanical transmission is required between the engine and rear wheels which also robs horsepower. Another point could be made for the mid-60's when the transition occurred from the generator to the alternator. The alternator design was adopted due to the lower RPM amperage output being so much better. But, at what cost for efficiency? I'm siding with Bill Basore on this one. Anytime you make an electrical or mechanical conversion, it wastes more energy.
 

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Of course, you can always play around with pulley sizing to make your accessories (and that includes your alternator) spin faster or slower as you see fit. That is why under-drive pulleys are worth so much horsepower - it takes engine horsepower to drive the water pump, alternator, power steering pump, air pump and a/c compressor. A smaller crank pulley will drive all of the accessories slower for better high-rpm use. A larger accessory pulley will do the same thing for that one accessory. A smaller accessory pulley will make that one unit spin faster. That is why in most cases for high-rpm use, you'll see a smaller crank pulley to drive the power-robbing water pump slower, and a smaller alternator pulley to make it spin the same as it did with the original setup.

The 470hp 393W in my Crown Vic uses the stock two-row radiator, stock fan w/thermo clutch. It does not overheat even when I switched from the stock 7-1/4" crank pulley to a 4-1/2", although my alternator is having issues... I'll probably put a 5-1/2" pulley on it.
 

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My situation may not be the run of the mill, but I have reasons for using electric fans. I do understand that the alternator takes power from the engine, and as the load on the alternator increases, it takes more power. Mainly I did mine for aesthetics, but also the thought of a mechanical fan coming apart at 8000 rpm (would be more like 10 or 11000 with the pulley ratios) scares the hell out of me. I have roughly 600 ponies at the crank out of a 351 that is only street driven, so I could care less about a 10 or 15 horsepower loss. I get more loss through the trans than anything, that would be the place to look if someone wants some ponies back. I also went with a 180 amp 3G alternator. Once the power is applied to a 3G, they are hard to spin, and they really need a serpentine pulley on them. The original 65 amp would be better if you want to keep horsepower. A 3G creates a lot more juice, but creates a lot more drag at the same time. I still have problems sometimes with my belt slipping on the alternator pulley.

At any rate, electric fans can be very efficient if set up right, even the lower amp inefficient ones like I have. They are also much safer, just ask RagCat. Also, if a mechanical is just a tiny bit out of balance, they will destroy your water pump.

I know several people that have had issues with cooling after converting to electrics fans. They always say "It cools fine until I come to a red light", well duh. You MUST seal it well to the radiator, just putting it on and pushing those plastic radiator mounts through ain't gonna cut it. A fan will pull air from the point of least resistance. In order for it to pull air though the radiator, you need to make the radiator the point of least resistance. Shrouds are the most important part of a mechanical fan setup, the same goes for an electric setup. If you seal and cover the whole radiator, you can make an electric setup work just as good or better than a mechanical. I have all of about 60 bucks in my setup, that includes 2 fans and the controller (shroud was free).



Granted, I only have about 300 miles on the car, but it works like a charm. Have driven it on a 92° day and the temp never went over 195°. I also let it idle in my driveway for about 30 minutes to see if I would have any traffic light troubles, never got above 180° then. The trick is to set it up so that the fans can only pull (or push) air through the radiator, and it should be setup so that it comes from the entire radiator.
 

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1970fastcat is re conferming my thoughts---the big block in our 67 would not stay cool after a heat soaked run down the highway with a stock fan and shroud---just changing to an alum rad made little difference---putting on the dual 11" spal fans did the trick--the spal pwm controller was icing on the cake--the starting amps (or watts) on the 25/30 amp EA fans can be 150% so the system starts the fans at a lower speed and/or @ different times---keeping the surge @ a minimum
now to really stir up the pot---copper disaptes heat far better than aluminum---but the lead solder used to attach the fins to the tubes is a terrible material to transfer heat--the furnace braze techniques used on the alum rads makes a better thermal connection between the fins and tubes than copper---the guys who make race/nascar radiator use alum--i think it's a crap shoot---the WHOLE system needs to work together--my 47 sedan had a new walker radiator (brass/copper) and it always ran hot @ 70 mph with the a/c on---it had a 4 core--5/16 on c/l tube spacing--and a fairly high fin count per inch (like 14 or 16)----i replaced it with a 3 core , dimple tube brass/copper (beko rad--concord,ca)--7/16 tube c/l and 9 fins per inch---the car won't ever go past thermastat temp !!all the things i hated about that car went away with a simple radiator change--most of use have no problem spending thousands of $$$ on an engine trans combo but cringe @ a $ 450.00 radiator that protects that combo--thats life
doctordesoto
 

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Discussion Starter #19
Mike that is a sweet shroud. Thanks for the picutre. I wasn't thinking about actually blocking off the non-fan area at the back of the rad. I would think that would hurt the cooling but obviously not.

I'm still doing more research on this one but in the end I think it's safe to say there are arguments both ways and it's not about a "best" solution but whatever is best for your application. I'm going to try electric and see how it all goes down.
 

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Keep in mind that it isn't just blocked, it's shrouded. The shroud sits 3/4" behind the radiator, that way it seals all the way around it, but lets air move past the tubes and fins even in the areas that aren't directly in front of the fans.

I had one of my metal suppliers make it for me. They work with break metal a lot and made it out of .063 aluminum sheet. They put a 1/2" break all the way around it and 1/2" outward break on the sides for mounting to the radiator. I cut the holes in it with some electric shears and screwed a piece of 1/2" aluminum angle down the center for a little added support. It works much better than I ever expected.
 
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