Cooling fan CFM specs & Vairable pitch option

[Will L.]

As always, if a moderator feels relocating this thread is best, please do so- I just guessed at this section.

I am wondering if anyone has any CFM specs on any of the fans used from gmt400, Hummer/hmmwv or duramax fan.

I vaguely recall @WarWagon throwing out a number or two in the past but can’t recall if those were just electric or what.

In working on the hmmwv fanclutch adapter to spin on waterpump, an old thought of what is the best fan, yet available came up. Making an adapter to a non available fan or second rate fan seems dumb at best. So this lead to chasing variable pitch fans. I found some that aren’t insane expensive, but need some solid reference points to work off of.

I have the GM 15992650 long known best airflow of the gmt400, which according to John Kennedy fows better than the duramax fan from his testing. I also have the 6003064 Hummer blade that the AM General guys said was the best metal Hummer blade (I lucked out there), but idk what numbers the plastic ones did or if they are better or worse.

The variable pitch seems like a great idea to me, cuz I could set mine for max cooling, and ignore mpg. Others might adjust thiers for less cooling and better mpg.

There are also other fans I have found that are serious air movers that are fixed angles but again, need cfm specs to know what to compare.

As always any info is appreciated and any mild to wild concepts to share welcome.

 

[ak diesel driver]

Good luck on finding CFM numbers.

 

[Will L.]

Yeah, right? Haha. I figure you chased them on your fan um expedition...excursion...cant remember the pun name here.

 

[WarWagon]

Our fans are over 10,000 CFM. I took the TrailBlazer SS fan tested below and put it in "Patch". I immediately removed the useless fan from "Patch" after towing a load to Lake Havasu in 117 degree weather with the windows down and heater on high because it, at 10,000 CFM, didn't have enough blade pitch (and thus CFM) to keep Patch cool. I had smashed the KD fan clutch and steel fan with an Elk. This was the first trip after rebuilding a truck from the salvage parts. I put in a Dmax fan when we got back and problem solved. OOPS on my part as I thought 21" fan was a 21" fan forgetting about pitch.

I dug into this on a Trailblazer SS. I was asked to test some electric fans. I talked them into doing a thicker radiator instead because the mechanical fan couldn't close a lower temp T-Stat. Now discontinued Ron Davis radiator from Simple Engineering with the mechanical fan did close the lower temp T-Stat. The factory radiator wasn't thick enough for the 6.0L LS2.



To come up with CFM I took a race track wind speed meter and measured several points across the radiator in a grid. I averaged the MPH because with the fan circle above the radiator it's a airflow mess worthy of a GM like a LLY intake. CFM is dependent on engine RPM!

Even I am not crazy enough to measure MPH when the fan belt has reached it's limit at 5300 fan RPM screaming, squealing, while slipping. I run into the EV fan system limit at a little over 4000 FAN RPM, the belt noisily reaches it's limit at 5300 RPM. 4000 fan is ~3500 engine RPM. Possible road speed and ram airflow would raise this limit. Note engine RPM math has to include 90% max lockup of clutch

A popular mod for the TBSS was a LS1 electric fan adapted to replace the clutch fan. Frankly stick a fork in electrics at anything over 1200 RPM as the mechanical fan has higher CFM from there on up.

LS1 type replacement fans
12 LBS assembly plus any brackets and relays.
4"-5.25" deep. (Tips of motors)
18.3" tall
28" Wide.
2 electric fans
6 blades per fan
2.5” Fixed blade length
1” blade depth.
12.25” Fan dia (24.5 total fan area) Rest is blocked off.
4.25” Motor dia blockage center of fan
Lots of free space between blades.

Free standing, no radiator resistance for the electric test:

2400 RPM on battery voltage.
(2500 RPM in reverse oops!)
4925 freestanding CFM on battery power: avg 16.6 MPH. Installed CFM was not tested, that is radiator and hood down restrictions that lower the CFM of any fan.

Mechanical fan radiators in place and hood closed: (No cheating like electrics are rated without these restrictions in place - if they were the electric fan CFM would be lower.)

The fan and clutch assembly is 9.8 Lbs of rotating mass. (Shroud not weighed.)
Fan is in overdrive: Drive ratio 1:1.280
Blade count = 10
2.5” blade depth (pitch)
3.75” to 5”, inside to outside, blade width
Diameter 21” (Wow!)
9.75” of the center wasted due to clutch and fan center blockage.
No free air space between blades. (High suction ability for restrictive radiator stacks.)
18.75” shroud Diameter – rest used for double ridge air seal and noise control I guess.
13.5” from bottom to upper restriction on shroud. Upper shroud restriction is 3” from fan. This is from fan center being too high for radiator location. Top of fan circle is over the top of the stack.

First test: 'idle'
600 ENGINE RPM
768 FAN RPM
6.94 MPH avg airflow
2050 CFM

Second test
~1200 ENGINE RPM (Fast as HPTuners can command)
1472-1504 FAN RPM
14.62 MPH avg airflow
4350 CFM

Third quick test
800 ENGINE RPM
9 measurements all are +3 MPH over 600 RPM
10 MPH rounded up .06
2975 CFM.

Last test
~3024 ENGINE RPM (helper on throttle)
3424 FAN RPM
35.46 MPH avg airflow
10500 CFM

RPM differences? Yes, because the fan clutch even at full lockup is slipping reaching what I would call the torque limits. This is why the cooling fins are on them: wasting power.

 

[Will L.]

Ok, that is some helpful info. Thank you.

Currently talking to a guy, there is a 22” fan, that at 3600 rpm can push as low as 9,000 cfm to well over 21,000 cfm depending on adjusted pitch. But also goes from 6.5 hp to a gulping 23 hp used.
This is without a fanclutch. Adaptation is needed. And bringing the blades down to a 20” range would obviously lower the numbers. About 5 lbs in weight.

A long ways to go in figuring this out yet obviously. But if we are playing with less than 11,000 and we could see a 50% increase... I am not letting go of this idea easily.

 

[WarWagon]

You mis-understand. 10500 CFM is for a TrailBlazer SS and NOT enough for our trucks. The duramax fan and steel 9 blade fan deliver way more than 10500 CFM. I was running hot with the TrailBlazer SS fan because it doesn't have enough blade pitch.

The fan could also have flexed too much as these plastic fans can act like a flex fan.

To measure our fan one could ruin a fan clutch and lock the spring in full lock position. Then run MPH tests at diffrent engine RPM. Average MPH. Measure radiator and calculate CFM.

 

[Will L.]

Oh, ok. Shucks!
Well if I can get something set up to measure my blades, seems to be best option then still.

 

[Will L.]

I posted same thread on Hummer forum incase anybody there new any details.

This is a snipit from the case study done by Ricardo when they redesigned the hummer from the 6.5 to the duramax:
“With a new 6.6 litre engine producing 300 horsepower and 520 lb-ft (705 Nm) torque, it is not surprising that the cooling system would also be an issue for the AM General and Ricardo engineers to resolve. Heat rejection from the Duramax 6.6 litre is significantly greater than for the previous 6.5 litre engine – so as a result a larger cooling pack was needed, incorporating six separate component-specific coolers.
As Reedy explains, “We knew that the old engine cooling fan, at wide open throttle, was capable of drawing about 4200 cubic feet (120 m3) per minute of air through the cool pack. Clive Hughes and hisThermal Systems team at Ricardo did some early comprehensive analysis work and determined that we needed to draw more like 7900 cubic feet per minute through the cool pack to get the right amount of heat rejected.”

Only detail is those specs are what is going through the stack, not fan only. But some solid numbers to work back from. Maybe a place to contact about more specs.

 

[WarWagon]

Restrictions reduce CFM. So I am assuming the TBSS fan delivered X CFM in our trucks. It may not. The bias I was thinking of was "freestanding" electric fans vs. in place restrictions (radiator) of the mechanical fan delivering 2X the CFM.

 

[THEFERMANATOR]

My question about the other fans is there cfm free flow or through a cooling stack. I believe part of the reason kennedy said the 9 blade steel did better was he compared it to a duramax fan using a 2000 shroud. GM swapped to a 454 shroud when they went to the 9 blade steel fan. When you install a duramax fan you'll notice not much of the fan blade is sticking into the fan shroud which kills a fans efficiency. So I think thats why his testing found the 9 blade steel fan to be better than a 21" duramax blade.

How large a diameter fan blade can you run? The 06+ lbz uses roughly a 23" fan, but it moves some SERIOUS air. Or the 11+ trucks use a 25" fan blade in them. You may want to also take a look at the early kodiak blade. It's listed as 21 inches and has a ring around the outside of it to seal to the shroud better and prevent the blades from flexxing.

 

[WarWagon]

I know the 2008 HD duramax like our 2500 had a 25" fan.

Yeah, position of the fan in the shroud is critical.

KD had mentioned the fan flex as one reason the steel did better/same. This explains why the dmax fan pulls more air at idle but evens out at higher RPM. It's my observation the dmax has better AC performance at idle.

Either fan performs the same in keeping me under 210 ECT.

 

[Will L.]

This is one of the companies I have looked into. I will post a pic incase the link dies later for reference.
http://www.hoverhawk.com/

The company cuts down fan blades to what is needed frequently and affordable. So going to a 20” fan is no problem, and you can compare 22vs24vs26 and get the relative idea on a 20” both cfm and load.

They also said, yes these fans are designed to run behind radiators all the time.

Fans cfm in design can be rated free air or either obstruction. But when the obstruction could be variable, they usually rate based on free air. For isntance all electric fans for aftermarket are rated free air- not because it advertised better, but same fan could be used on 1988 Chevy pickup or a 2018 Chevy pickup and the cooling stacks are tremendously different.

When automakers design it, they pretty much know what the cooling stack will be for that rig, so they design the flow based on that load and work the numbers to where they get flow required as to not waste fuel turning too much fan.

I really like the adjustable fan pitch idea, because you can see in the 22” range from 9k to over 21k cfm!!!
Under 5hp to over 23 hp! HUGE variations.

The adjustment is made on the bench, not in place. But to be able to fine tune your cooling and mpg loss from it- win in my book. In talking to the guy from this company he said, it really is as simple as know the open air cfm of current fan, and being able to adapt this fan. Factoring in of corse the weight and hp load.

But having a “nut/flange” adapter made to hold this type of fan on a spin on waterpump or for the 4 bolt hold out guys, an extension flange spool... seems simple to me.

I started chasing this from wanting the best fan available to go onto the hmmwv 100% lockup style clutch, and am still pursuing it that way. But IF a viscous fanclutch could hold the load and a person can get more than enough air from it anyways...why not?

 

[WarWagon]

Bingo. The viscous fan clutch may not be able to take the CFM the fan wants to move and just slip instead.

Make sure more airflow is needed as some cases the radiator is too thin. AKA can't use all the airflow.

 

[Will L.]

If it flows “too much” it would just cool quicker. So less engaged time.

And the viscous clutch possibility slipping more is why I want to try the hmmwv fan clutch. On/off.

But now on the hummer forum guys are pushing again about a hydraulic motor to spin the fan so it can be against radiator like it should be. That would obviously eliminate fanclutch all together. A 24” fan could fit on hummer radiator if not for the angle. Instead it is 19.5”-20”. I’ll find some pics to show how rediculous...

But if these style fans would make the difference, wouldn’t need to change angle of fan. Same “fix” could Be for pickups and hummers.

 

[Will L.]

So the opening for the fan blade is for 20” fan and is vertical like pickups. The angle of the flat side it to the radiator. Look at the rediculous blockage and flow expected, and consider the radiator fins and tubes are straight like a normal pickup radiator.

Gee, i wonder why they dont flow enough- haha


I stole the pic from Dave @ bluehummer. Com

 

[Sand]

"Ridiculous" is an engineering understatement.
I like "epic fail "
Lol