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How do I determine electric fan CFM needs? #2942524
07/13/21 02:03 AM
07/13/21 02:03 AM
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Aurora, CO
jbeintherockies Offline OP
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Hello,

I'm trying to figure out how much CFM I need to pull through a big block Chrysler Summit 4-core radiator (radiator link) to keep a street/strip 440 cool. Is there a formula to use (ex: engine HP to BTUs)? I read a good rule of thumb is to have fan(s) that can pull 2500cfm for an 8-cylinder (how to choose an electric fan). I was looking at this shroud and fan combo from summit racing (kit link). However, it advertises only 1500cfm, which may not get the job done. I am trying to help my dad; it is his car.

The car is a 1967 Plymouth Satellite with a street/strip 440, Indy EZ440 heads, .530/.232@050, 10.8 comp, 22 degrees initial/37 total timing (we are in Colorado and he uses race gas), auto, 4.10s, flowkooler pump, 160 thermostat, factory fan shroud with a flex-a-lite fan (no viscous clutch installed; but he has one that could be used). It is an original big block car, so it has the larger radiator core support opening. The trans cooling lines are going into an external cooler and then into the radiator. I am not sure why the guy who built the car went that route; but I may try to bypass the trans oil lines going into the radiator. That might help. I also need to check that the radiator cap fits the radiator neck correctly and the pulley sizes. The car overheats (230+) in traffic, but runs around 190 or so cruising down the road. I believe the issue is airflow.

Questions/comments/concerns/thoughts?

Thank you in advance.

Re: How do I determine electric fan CFM needs? [Re: jbeintherockies] #2942533
07/13/21 05:38 AM
07/13/21 05:38 AM
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A few suggestions and questions:

Read the very long “Mercedes electric fan” thread in the questions and answers.

Search for and read the Stewart Components cooling tips.

I assume you are at an altitude of 5000 feet and air temperatures in the 95 to 105 degree F range?

Will the car reach 230 degrees coolant temperature idling in your driveway on the hot days?

Has the car actually boiled over and ejected coolant?

What antifreeze make and water mix percent is presently being used?

It there a modification that prevents you using a factory stock fan?

You might ask around among friends and family as to whether someone already owns a wind speed device like the Kestrel, and a good IR gun, preferably one that also has an external type K thermocouple probe too. If not consider purchasing these.

Re: How do I determine electric fan CFM needs? [Re: 360view] #2942541
07/13/21 07:25 AM
07/13/21 07:25 AM
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Just went through all the cooling problems with my Hemi Dart clone. Aluminum radiator, 165 thermostat, duel electric fans from the radiator builder claiming they would cool a 1000 HP engine. The car would climb to 230 degrees quickly. After going through everything to solve the cooling problems it turned out to be the fans were not pulling enough air. Put on a pair of 13 inch SPAL electric fans, mounted to a home made aluminum shroud. Now the car never goes over 190 degrees.Go on SPAL's website and pick the CFM rating you are looking for. The duel 13 inch low profile ones I bought pull 3560 total CFM and work great. I will not use any other brand after my experience. Search the internet for best pricing if your go with SPAL fans. Hope this information helps you.

Re: How do I determine electric fan CFM needs? [Re: maximus] #2942582
07/13/21 10:52 AM
07/13/21 10:52 AM
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I've been down this road with my Cuda, so I'll make a few hopefully helpful comments: make sure your charging system and wiring is up to snuff. I highly doubt that the typical 79A Mopar alternator will cut it. The stock 12 ga charging wire will definitely not be sufficient, so start thinking about a higher output alternator and a much bigger charging wire. You also need to decide on your fan control system. Are you going to simply use a switch to turn the fan(s) on/off? Probably not the best idea for any sort of city driving, so think about what fan controller you want. There are many different options available.
Just wanted to mention these things, because they are often overlooked, but they are equally as important as choosing the fan(s) themselves. I can go into more detail about what I have done if you want.
Hope this helps.

Re: How do I determine electric fan CFM needs? [Re: 360view] #2942712
07/13/21 05:58 PM
07/13/21 05:58 PM
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Aurora, CO
jbeintherockies Offline OP
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Quote
Read the very long “Mercedes electric fan” thread in the questions and answers.

Search for and read the Stewart Components cooling tips.


Will do!


Quote
I assume you are at an altitude of 5000 feet and air temperatures in the 95 to 105 degree F range?


Around 5280, yes. Air temps are in the mid-to-high eighties F; not quite 95-105.


Quote
Will the car reach 230 degrees coolant temperature idling in your driveway on the hot days?


I don't know, never tested that


Quote
Has the car actually boiled over and ejected coolant?


Yes


Quote
What antifreeze make and water mix percent is presently being used?


I think it is Oreilley 50-50 mix. I know he has added "Water Wetter" and the VP Racing "Madditive" (Madditive link) additive.


Quote
It there a modification that prevents you using a factory stock fan?


None. But it the current factory stock fan shroud and flex fan aren't getting the job done, why do you think a switch to the factory fan would? I am not a fan (no pun intended) of flex fans. I run a factory setup on my small block barracuda and it works great. But I have a two-core radiator, not a four core. I can try the factory fan and clutch and see how it goes.


Quote
You might ask around among friends and family as to whether someone already owns a wind speed device like the Kestrel, and a good IR gun, preferably one that also has an external type K thermocouple probe too. If not consider purchasing these.


I have a Craftsman IR gun, but it doesn't have the external thermocouple probe. I think my voltmeter has a thermocouple probe; I'll have to check that.

Re: How do I determine electric fan CFM needs? [Re: maximus] #2942713
07/13/21 05:59 PM
07/13/21 05:59 PM
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Aurora, CO
jbeintherockies Offline OP
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Originally Posted by maximus
Just went through all the cooling problems with my Hemi Dart clone. Aluminum radiator, 165 thermostat, duel electric fans from the radiator builder claiming they would cool a 1000 HP engine. The car would climb to 230 degrees quickly. After going through everything to solve the cooling problems it turned out to be the fans were not pulling enough air. Put on a pair of 13 inch SPAL electric fans, mounted to a home made aluminum shroud. Now the car never goes over 190 degrees.Go on SPAL's website and pick the CFM rating you are looking for. The duel 13 inch low profile ones I bought pull 3560 total CFM and work great. I will not use any other brand after my experience. Search the internet for best pricing if your go with SPAL fans. Hope this information helps you.


Thanks, I will definitely keep your advice in mind if we go the route of electric fans.

Re: How do I determine electric fan CFM needs? [Re: mrob] #2942716
07/13/21 06:13 PM
07/13/21 06:13 PM
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jbeintherockies Offline OP
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Originally Posted by mrob
I've been down this road with my Cuda, so I'll make a few hopefully helpful comments: make sure your charging system and wiring is up to snuff. I highly doubt that the typical 79A Mopar alternator will cut it. The stock 12 ga charging wire will definitely not be sufficient, so start thinking about a higher output alternator and a much bigger charging wire. You also need to decide on your fan control system. Are you going to simply use a switch to turn the fan(s) on/off? Probably not the best idea for any sort of city driving, so think about what fan controller you want. There are many different options available.
Just wanted to mention these things, because they are often overlooked, but they are equally as important as choosing the fan(s) themselves. I can go into more detail about what I have done if you want.
Hope this helps.


All good advice. We are both well aware that the current factory square-back is not going to get the job done if my dad decides to go with twin electric fans. The charge wire has been upgraded already to either 10 or 8; I forget now. I was planning on using two relays to control the fans. The fan closest to the radiator inlet would turn on when the ignition key was set to the 'run' position. So it would always be running when the engine is running. I was going to use this relay setup (Hayden Auto Relay) to control the other fan and have it come on at around 185 or 190 degrees. I am aware of electronic fan controllers (ex: Dakota Digital electronic fan controller); but was trying to stay away from something like that.

I am curious, what shrouding and fan setup did you go with? Did you try hard to get a factory setup (factory shroud, factory fan, factory viscous clutch) to work before going electric? I am very much in favor of staying with the mechanical if possible; but I have my doubts that is going to work in this scenario.

Re: How do I determine electric fan CFM needs? [Re: jbeintherockies] #2942749
07/13/21 07:46 PM
07/13/21 07:46 PM
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jbe, in response to your questions:

Depending on the amp draw, 8GA or 10GA may not be enough. To give you an example: a popular Spal dual fan combo is P/N 30102052 and consists of dual 11 inch, 5 bladed paddle fans. At 0.6 inch pressure drop (basically the resistance through a thin radiator), they draw around 33A. Thicker radiator cores will draw more amps, so keep that in mind. On top of that the 33A draw is especially bad at idle when the alternator isn't spinning that fast. I don't know what all of your electrical loads are, but I ran 6GA cable from the alternator through a 150A fuse to the positive lug on the starter relay (which is connected to the battery).

Your idea about having one fan running all the time isn't bad, and only controlling the second fan with a temperature driven relay will definitely help lessen the "shock" of 2 fans kicking on simultaneously. I use the Dakota Digital controller that you mentioned to perform in a similar way. I set the one fan to come on at a low temperature and keep it running basically all of the time. The second fan just kicks in when the first fan doesn't cool enough (usually when idling).

I ended up with the Derale 16833 shrouded fan kit because it fits a 26 inch wide core pretty well. Beware, the fan cfm specs that Derale give are overblown! They claim 3750 cfm, but there's no way that's possible. I contacted the fan manufacturer about the fan specs and each fan is only capable of 1346 MAX cfm. So according to my math, that's around 2700 cfm total. Gee, that seems a bit less than 3750 cfm ...

I tried various mechanical fans. Different diameters, number of blades and blade pitches and none of them cooled my engine well at idle. The best combo was the 18 inch, 7 bladed Mopar fan with the thermal fan clutch. Even that fan wasn't enough to keep the temperature from creeping up at idle. There's nothing worse than watching the temperature gauge slowly creep up while you're sitting in at a stop light.

Hope this helps

Re: How do I determine electric fan CFM needs? [Re: mrob] #2942754
07/13/21 08:07 PM
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Flex fans do a real good job of not moving air. If you do have a stock fan to swap in, try that.

Re: How do I determine electric fan CFM needs? [Re: jbeintherockies] #2942762
07/13/21 08:17 PM
07/13/21 08:17 PM
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That is not a fan shroud, it is a air blocker.

Re: How do I determine electric fan CFM needs? [Re: 71birdJ68] #2942802
07/13/21 09:19 PM
07/13/21 09:19 PM
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I have the Cold Case radiator and fan on my 528 Hemi with air conditioning. Stays nice and cool about 190 all the time.

Re: How do I determine electric fan CFM needs? [Re: mrob] #2942828
07/13/21 10:48 PM
07/13/21 10:48 PM
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Originally Posted by mrob
jbe, in response to your questions:

Thicker radiator cores will draw more amps, so keep that in mind. On top of that the 33A draw is especially bad at idle when the alternator isn't spinning that fast.


That information is not quite correct. A thicker radiator with reduce air flow in most cases. Affinity laws state that for centrifugal loads like a fan, theoretical hp is the square of the flow and the cube of the rpm. That means that the power requirement (including amps) goes down quite a bit when the flow is reduced.

In addition, when you are idling, the voltage drops. Again the power is a cube of the voltage, so when the voltage drops the current drops quite a bit. Flow also suffers quite a bit.

In my race car, I went from a 55 amp alt to 120 amp. Gong down the track I went from 11.8 volts to over 13. Clearly the alternator was too small. The higher voltage increased fan and water pump speed to the point that on a hot day back at the pits car was 20 to 30 degrees cooler than before - usually around 20 degrees.


67 Coronet 500 9.610 @ 139.20 mph
67 Coronet 500 (street car) 13.300 @ 101.75 mph
69 GTX (clone) - build in progress......
Re: How do I determine electric fan CFM needs? [Re: 360view] #2942912
07/14/21 07:05 AM
07/14/21 07:05 AM
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If you are going to get serious about fan work, in addition to IR-gun, accurate thermometers, and electrical multimeter,
you are going to need to measure tiny pressure differences with a mini digital manometer.
After reading Amazon reviews I took a chance on a $36 HT-1890 “no name” Chinese unit and it has worked pretty well. These also can be valuable evaluating the low pressures of exhaust systems.

Years ago we had to use inclined tube mechanical manometers, some of which were 6 foot long and had to be perfectly level to read accurately.

Re: How do I determine electric fan CFM needs? [Re: jbeintherockies] #2943026
07/14/21 11:58 AM
07/14/21 11:58 AM
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Originally Posted by jbeintherockies
Hello,

I'm trying to figure out how much CFM I need to pull through a big block Chrysler Summit 4-core radiator (radiator link) to keep a street/strip 440 cool. Is there a formula to use (ex: engine HP to BTUs)? I read a good rule of thumb is to have fan(s) that can pull 2500cfm for an 8-cylinder (how to choose an electric fan). I was looking at this shroud and fan combo from summit racing (kit link). However, it advertises only 1500cfm, which may not get the job done. I am trying to help my dad; it is his car.

The car is a 1967 Plymouth Satellite with a street/strip 440, Indy EZ440 heads, .530/.232@050, 10.8 comp, 22 degrees initial/37 total timing (we are in Colorado and he uses race gas), auto, 4.10s, flowkooler pump, 160 thermostat, factory fan shroud with a flex-a-lite fan (no viscous clutch installed; but he has one that could be used). It is an original big block car, so it has the larger radiator core support opening. The trans cooling lines are going into an external cooler and then into the radiator. I am not sure why the guy who built the car went that route; but I may try to bypass the trans oil lines going into the radiator. That might help. I also need to check that the radiator cap fits the radiator neck correctly and the pulley sizes. The car overheats (230+) in traffic, but runs around 190 or so cruising down the road. I believe the issue is airflow.

Questions/comments/concerns/thoughts?

Thank you in advance.


Another data point: 1972 Dart, low-deck 451, .652/272@.050, 10.3 comp, 27 initial/36 total, 4-speed, 3.91, Flowkooler pump, 180 Milodon hi-flow thermostat, Champion 3-row 26" aluminum radiator, Ford Contour electric fans with Autocoolguy PWM controller.

Idles at 182 all day in 90+ degree weather. It does heat a bit on the highway (65 mph is 3300 rpm) and after 15 minutes it levels out at 198. Slowly comes back down once off the highway. This is probably due to the Contour fan shroud blocking airflow when the fans should not be needed at highway speed, but I can certainly live with temps at or below 200. Especially since it stays cool in stop & go (or just stopped) wink

Something to watch out for, besides the electrical upgrades which have already been mentioned: more small cores (4) is not better. All that metal interferes with the airflow and the multiple small tubes don't have as much heat transfer capability as fewer large tubes... IMHO the best radiator to use is a two-row with 1.25" or even 1.5" tubes if there is room between the core and the engine.

Chevy HHR fan is supposed to work well but I'm not sure it'd be big enough either. Also a Lincoln (Mark VII?) fan is a good one. But the Contour dual fan is cheap and readily available.

The additional trans cooler probably helps a bit, but I would not use it instead of the radiator cooler. It'd have to be pretty big depending on the converter... work

Last edited by DrCharles; 07/14/21 11:59 AM.
Re: How do I determine electric fan CFM needs? [Re: DrCharles] #2943093
07/14/21 02:12 PM
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Quote
Something to watch out for, besides the electrical upgrades which have already been mentioned: more small cores (4) is not better. All that metal interferes with the airflow and the multiple small tubes don't have as much heat transfer capability as fewer large tubes... IMHO the best radiator to use is a two-row with 1.25" or even 1.5" tubes if there is room between the core and the engine.


I like the two core radiators, too. But, my dad bought a four core and that is what I have to work with.


Quote
The additional trans cooler probably helps a bit, but I would not use it instead of the radiator cooler. It'd have to be pretty big depending on the converter...


It has a 10" converter. I will leave it as-is for now.

Re: How do I determine electric fan CFM needs? [Re: NITROUSN] #2943094
07/14/21 02:15 PM
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I have the Cold Case radiator and fan on my 528 Hemi with air conditioning. Stays nice and cool about 190 all the time.


What shroud? Electric fans I assume?

Re: How do I determine electric fan CFM needs? [Re: 360view] #2943096
07/14/21 02:20 PM
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a good IR gun, preferably one that also has an external type K thermocouple probe too. If not consider purchasing these.


What areas am I probing with the thermocouple probe, around the radiator core itself?


Quote
you are going to need to measure tiny pressure differences with a mini digital manometer.


How do I use a manometer? Where on the car would I be using it and when?

Re: How do I determine electric fan CFM needs? [Re: Sniper] #2943098
07/14/21 02:22 PM
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Originally Posted by Sniper
Flex fans do a real good job of not moving air. If you do have a stock fan to swap in, try that.


My brother has a factory fan not currently being used; not sure what diameter or blade count. I can try it with the clutch and see how it goes.

Re: How do I determine electric fan CFM needs? [Re: 71birdJ68] #2943099
07/14/21 02:24 PM
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Originally Posted by 71birdJ68
That is not a fan shroud, it is a air blocker.


Yea, cruising down the highway would probably result in HIGHER temps using Summit's "shroud". I'll keep looking.

EDITED: Re: How do I determine electric fan CFM needs? [Re: jbeintherockies] #2943735
07/15/21 09:30 PM
07/15/21 09:30 PM
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All of my temperature evaluations start with a 1/8 " tubular thermocouple probe adapted into the intake manifold as close as possible to the thermostat. Do be careful not to BURY the probe against the bottom of the opening/port as it will impact the readings and sensitivity. This will put the probe in direct contact with the coolant as it is leaving the motor. The main reason for using Thermocouples is they are extremely accurate, sensitive, don't lie, nor do they need calibration. The meters may but rarely do unless abused.

You can buy extension leads to run inside the car and watch the actual temperature changes. most Digital multi meters today have a plug in for the T/C's. Make sure you get the correct type of probe and extensions for your particular meter. Type J and K TC's & extensions appear to be, BUT are not interchangeable and will skew the readings. Both types are available inexpensively on eBay or Amazon as well as various meters / DVM's etc. An example is of the probe is in the link just below this paragraph. I'm sure there are others and possibly less expensive. I use an 1/8" oil pressure line compression fitting and adapt it up to what ever size is needed. The metal portion is also bendable to a point but not on a repetitive basis. If you are careful and do not overtighten the fitting you can move the ferrule or carefully remove it to allow repositioning for the next use.
THERMOCOUPLE EXAMPLE LINKY

You may be surprised at things that affect the temperature, like a semi changing lanes in front of you and the temp starts ticking upward until you fall a good distance behind him. Going north on I-29 can make the temp climb a bit, while turning around and going south makes it drop. This is on what appears to be level ground.
These scenarios have repeated many times with different vehicle's over the years.
As we all know, gauges can be wrong for many reasons, IR guns are good for a general indication but they need to be calibrated for the surfaces / coatings they are reading as well as the distance from those surfaces there are many variables that can affect their accuracy.
keep us posted beer

Last edited by TJP; 07/16/21 11:56 AM.
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