(2) 12" fans versus (1) 16" fan

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I didn't realize there were so many experts out there. This site is great!
 
If your using a 26” radiator probably the best fan is a Mercedes fan from the C class. I use this on my E-body 26” radiator and it will cool it running at 25% fan speed @ idle. The most I’ve seen it go is 50%. The drawback is it needs a controller and I’m not sure about the space on an A-body.
There is an extensive write up on Moparts if anyone is interested.

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I'm a firefighter by trade, so I have pretty extensive training on your example for positive pressure ventilation as it's how we clear smoke from houses. It's not a great comparison to begin with as there are a lot of differences between the examples that make the comparison fairly irrelevant. The air has to flow through and out of the engine compartment, for example, so the shroud isn't even close to the only thing that effects flow if you start considering the whole system. And it's not the biggest. The airflow out of the engine compartment would be a much larger factor for creating any kind of positive pressure and reducing flow through the radiator than even a fairly restrictive shroud. What you're talking about has more to do with the aerodynamics of the car as a whole than a fan shroud.

A few other issues- the fans shouldn't even be running if the car is moving at any kind of speed. If the radiator and the rest of the cooling system are operating properly the fans shouldn't even be on if the car is moving more than 25-30 mph, so all of the airflow at that point is from the speed of the vehicle which should be more than enough volume to be able to overcome a little extra resistance from the shroud. Meanwhile, when the car is moving slowly or not at all the shroud allows the fans to pull air across the entire core. The factory used shrouds for the stock mechanical fans, going without a shroud just reduces the efficiency of the fan regardless of whether it's mechanical or electric.

That's one of the reasons I used a factory electric fan set up. It has a shroud that was designed to work with the fans that it's equipped with over the surface area of that size radiator. Some of the aftermarket shrouds are a just a flat plate with holes for the fans- that's just a bad design. Same deal with fans that come without a shroud, you have no idea if you'll actually get the rated CFM because most likely the rated CFM was achieved using some kind of shroud for testing. If you don't replicate the testing parameters you won't get that kind of flow.



Yes, there are shrouds out there that have flappers and things that would be open when driving and closed when the fan is running. I personally think they're kind of gimmicky, the air flow through the shroud at speed has to be pretty darn restrictive before something like that is necessary or useful. Basically it's a band aid for a poorly designed shroud or undersized fan area.



Yes, you absolutely have to balance the entire system. All the components have to work together for the system to work the best. Sure, you can overcome some amount of undersized fan by running a larger radiator, or overcome a smaller radiator by using a much higher rated fan. Same goes for the water pump, pulley ratios, etc. But for best overall performance and efficiency everything has to work together. Run more fan than you have to and you're losing horsepower driving the fans. Run more radiator than you need and you'll lose space which may require running smaller fans, which could cause in traffic overheat issues when you're not moving enough air. Run too much water pump and again you're losing power driving the pump, plus you may lose cooling efficiency if the water isn't staying in the engine long enough to absorb heat.



If your system works that's great, it sounds like you have a fairly complicated set up with the twin turbos and intercoolers so going beyond the standard kind of set up and thinking may be totally necessary. A 200 amp alternator is something a lot of us don't have though, and something the stock wiring harness probably won't tolerate for very long. I was just pointing out that your CFM requirements, and therefore your amperage load to run the fans, would probably be lower with a well designed shroud. Of course, a poorly designed shroud may not help much at all.



Yes the Black Magic fans have a great CFM rating, but they come without shrouds so there's no guarantee they'll flow that much on your car. Plus, you can get fans that flow more air for half the price and were tested to go over a 100,000 miles.

I agree when going above the regular requirements, but the alt I have is a mopar looking one and also converted to 1 wire so stock wiring is out, but they have lower amp ratings as well, just have to compensate for the draw when adding to the charging system. Yes I have rewired the whole car with new wire, my setup should work for my setup still fabricating a few things still. Again I agree with what your saying, just putting how I did things out there.
* wow just looked at the black magic dual fans they pull 28amps, my 4 only pull together 12amps. Wonder if anyone's done a true comparison from 4 low amp to two high amp with a shroud test?
 
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thanks Fire Guy
WE did extensive for Chrysler on the grades of the California desert
The grapevine, the "Baker Grade" The 29 Palms hill
Shrouds work
Spoilers work on the raising the pressure in front lowering behind the radiator problem
and we found that slow pulls with a tailwind the hot air was just going around and around under the core support
IMHO there is not a electric that will work with a big motor and a loaded trailer
I use a 9 blade fan on my truck which is a FSB upgrade from the oem 7 blade high pitch fan
GM has an 11 blade (on my motorhome) which I need to try this summer
I have a two fan pusher off a Merceedez or bmw - had to trim the grille
really helps in stop and go and makes the AC work better
I use a 73 400 jn the speedo line controller to turn the fans off at 28 mph (they controlled the vac advance)
on radiators frontal are is best but do what you have to do
sometimes you can use a big block core support
no flex fans or plastic
 
I have to disagree. If you have a room that has air (from a fan or the wind) blowing into it, the room will pressurize and once it reaches equilibrem there will be no flow. If on the other hand you open a window on the other side of the room you will have some flow thru the room. The amount of flow will be decide by either the opening in the inlet or the outlet.

My point is that a lot of driving is done at a speed where the fans are not pulling more air than the airflow of driving is providing and a poorly designed shroud will block air flow.

A 1/2'' thick elec fan shroud , did block air in mine , the air flow isnt great with one that thin over all the rad.. Wouldnt work for me , but my engine produces a lot of heat !
 
I use a 2007 Chevy HHR fan to cool the 408 in my Barracuda (low 10 second street car). They are cheap (about 50 bucks), fully shrouded, pull a ton of air...works great. I have had one on my car for about 7 years now, no cooling issues. Just had to trim a little plastic off the fan motor with a dremil tool...then it dropped right in. It fits 22" radiators perfectly.
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If your using a 26” radiator probably the best fan is a Mercedes fan from the C class. I use this on my E-body 26” radiator and it will cool it running at 25% fan speed @ idle. The most I’ve seen it go is 50%. The drawback is it needs a controller and I’m not sure about the space on an A-body.
There is an extensive write up on Moparts if anyone is interested.

View attachment 1715492592

Looks awesome! I’d like to see that write up, do you have a link?

The only drawback is the single motor arrangement puts the fan motor right in front of the water pump pulley, so it would have to be pretty thin. That’s the nice part about dual fans, keeps the thickest part of the fan assembly away from the tightest clearance. But if it’s thin enough at the back of the motor that would be a great set up.

I agree when going above the regular requirements, but the alt I have is a mopar looking one and also converted to 1 wire so stock wiring is out, but they have lower amp ratings as well, just have to compensate for the draw when adding to the charging system. Yes I have rewired the whole car with new wire, my setup should work for my setup still fabricating a few things still. Again I agree with what your saying, just putting how I did things out there.
* wow just looked at the black magic dual fans they pull 28amps, my 4 only pull together 12amps. Wonder if anyone's done a true comparison from 4 low amp to two high amp with a shroud test?

Yes, but not everyone fully rewires their car for this. I haven’t. I run an amp gauge bypass and have my fans run off of relays but it’s all tied back to the stock harness.

I’m not sure your comparing apples to apples with the fans. Fans can be rated at start up or at steady state. The start up amperage is much higher than what they pull when they’re already running. With a 4 amp rating I seriously doubt that’s the start up amperage.

thanks Fire Guy
WE did extensive for Chrysler on the grades of the California desert
The grapevine, the "Baker Grade" The 29 Palms hill
Shrouds work
Spoilers work on the raising the pressure in front lowering behind the radiator problem
and we found that slow pulls with a tailwind the hot air was just going around and around under the core support
IMHO there is not a electric that will work with a big motor and a loaded trailer
I use a 9 blade fan on my truck which is a FSB upgrade from the oem 7 blade high pitch fan
GM has an 11 blade (on my motorhome) which I need to try this summer
I have a two fan pusher off a Merceedez or bmw - had to trim the grille
really helps in stop and go and makes the AC work better
I use a 73 400 jn the speedo line controller to turn the fans off at 28 mph (they controlled the vac advance)
on radiators frontal are is best but do what you have to do
sometimes you can use a big block core support
no flex fans or plastic

A 1/2'' thick elec fan shroud , did block air in mine , the air flow isnt great with one that thin over all the rad.. Wouldnt work for me , but my engine produces a lot of heat !

You guys are just silly. They make electric airplanes now, think about that for a second.

If a mechanical fan can cool a particular engine, so will an electric fan. All you have to do is match the cfm output of the mechanical fan, and all that comes down to is blade and shroud design and the amperage to the motor. The mechanical fan and shroud can already do it, so really it’s just matching the power and speed requirements with the electric motor.

Now, there might not be an off the shelf electric fan that will meet the requirements of your particular system because of the dimensions and power requirements, but that’s not the same as saying an electric fan can’t cool it.

I use a 2007 Chevy HHR fan to cool the 408 in my Barracuda (low 10 second street car). They are cheap (about 50 bucks), fully shrouded, pull a ton of air...works great. I have had one on my car for about 7 years now, no cooling issues. Just had to trim a little plastic off the fan motor with a dremil tool...then it dropped right in. It fits 22" radiators perfectly.
View attachment 1715492938

Also a nice set up! The other one that works for 22” radiators is the older Ford Taurus set up, I forget the year range. But I think the HHR fan is a little thinner?
 
I went with a Chevy HHR fan for my 408 build as well, but I wasn't satisfied with the mounting options. I wanted to use the mounts for the factory shroud, so I designed and 3d printed prototypes.

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Looks awesome! I’d like to see that write up, do you have a link?

The only drawback is the single motor arrangement puts the fan motor right in front of the water pump pulley, so it would have to be pretty thin. That’s the nice part about dual fans, keeps the thickest part of the fan assembly away from the tightest clearance. But if it’s thin enough at the back of the motor that would be a great set up.



Yes, but not everyone fully rewires their car for this. I haven’t. I run an amp gauge bypass and have my fans run off of relays but it’s all tied back to the stock harness.

I’m not sure your comparing apples to apples with the fans. Fans can be rated at start up or at steady state. The start up amperage is much higher than what they pull when they’re already running. With a 4 amp rating I seriously doubt that’s the start up amperage.





You guys are just silly. They make electric airplanes now, think about that for a second.

If a mechanical fan can cool a particular engine, so will an electric fan. All you have to do is match the cfm output of the mechanical fan, and all that comes down to is blade and shroud design and the amperage to the motor. The mechanical fan and shroud can already do it, so really it’s just matching the power and speed requirements with the electric motor.

Now, there might not be an off the shelf electric fan that will meet the requirements of your particular system because of the dimensions and power requirements, but that’s not the same as saying an electric fan can’t cool it.



Also a nice set up! The other one that works for 22” radiators is the older Ford Taurus set up, I forget the year range. But I think the HHR fan is a little thinner?
I `ve tried about 6 diff, elec set ups , even 3 at once , they wouldn`t keep mine cool.
I dont have room for a contour or hhr fan , and mounting factory shrouds on a crossflow presents another set of problem .
 
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