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The clutch fan cannot turn that fast, so you needn't worry about it. As the rpm increases, so does the air resistance to the fan which prevents it from overspeeding. If it were a "fixed" fan, you should be worried. Since it has limited rotational speed, you are OK.
Some folks, in their infinite 'wisdom', put a flex fan on a hi-revving engine. That is just an accident looking for a place to happen....
7T1. What you said isn't all correct. My l82 came with a factory thermal clutch. Very dangerous heavy 7 blade in a high rpm motor
hot days and heat the fan goes into lockup mode. Because of the bigger crank pulley and smaller diameter water pump it is over driven Yes the clutch has some slip even in lockup mode but let's say 10% the fans were not balanced and not made for higher rpm. Then add in modded shift kitted auto trannies with nearly instant gear changes and they had enough of them come apart that nhra banded them from any class 11.99 and faster.
this was back in the early 80s when most cars like my 79 came with them
I went to a 10,000 rpm model stainless steel flex. Like all the other drag racers. I never worried about it again. Moved much more air and had lots less rotating weight we didn't have all the choices of electric fans back then
To the poster NHRA came out with safety rules for a reason When you start thinking about over 6000 rpm. It's kinda like the guy on the motor cycle with no helmet or the tiniest cheap 1/2 helmet. If your head is not worth protecting, just go for it
I'm big on SFI parts. Did you know that stock heavy dampers break from the inner to outside ring. Did you consider your highly over driven alternator. I broke both of them back when my vette was fairly new.
I installed the metal flex shield exterior , sfi flex plate, and the tranny blast blanket. Oh drive shaft hoop. I always had the tech inspection covered
This is what I had in blue color. The biggest blades and fit our stock fan shroud. Rated to 10000 rpm. Big CFM. Compared to the dangerous heavy stock 7 blade
I was thinking about putting the stock fan back in, will it be able to handle 6600 RPM
It'll be fine... What do you think the L88 and all of the 435hp cars ran for fans?
I run a Hayden Severe duty clutch and stock 7 blade fan on our 396/425 and it has seen 6500 more then a few times.
Now if you were talking about long, sustained RPMS at that range, i probably wouldn't run a mechanical fan at all....but for short bursts like 1/4 mile runs etc, it'll be fine. Just use a good GM fan and clutch.
The engine may be turning 7K rpm; but the thermo fan is not. It can only turn as fast as the clutch will allow it to do. Once it reaches and rpm level where the air resistance is equivalent to the clutch resistance, it starts to slip. No way can it turn more than about 3000 rpm.
Any 'fixed-blade' fan you run will rotate at the same speed as the engine; and the forces wanting to tear those fan blade apart go up exponentially as the rpm increases. If you have a hi-rev engine and don't want to run a thermo fan, go electric.
The engine may be turning 7K rpm; but the thermo fan is not. It can only turn as fast as the clutch will allow it to do. Once it reaches and rpm level where the air resistance is equivalent to the clutch resistance, it starts to slip. No way can it turn more than about 3000 rpm.
Any 'fixed-blade' fan you run will rotate at the same speed as the engine; and the forces wanting to tear those fan blade apart go up exponentially as the rpm increases. If you have a hi-rev engine and don't want to run a thermo fan, go electric.
Exactly.... at 6k rpms, the fan is probably turning 4-5k... The clutch will start slipping a lot at higher speeds like that.
As a no cost, 4 bolt, 5 minute, experiment, I installed the fan and drove the car around.
It ran waaaay cooler, even waiting at stop-lights, and waiting for a train.
The cockpit interior of the car also stayed way way cooler.
It did seem to steal a tiny bit of horsepower, but that could just be me? Seemed that a cooler motor offset this?
Can I run this for a while like this for a while if I keep Rpm down? what RPM?
What type of fan is it?
How much H.P. is this wasting?
What the moral of the story? the electric fan with no shroud wasn't big enough, and no shroud was making air flow inadequate?
Yes, any mechanical fan will eat up some horsepower.... Your fan being a 5 blade and the smallest fan clutch likely isn't eating up much power.... Maybe 5-10hp...
My 7 blade with the severe duty clutch ate up 15 rwhp on the chasis dyno...
Whatever method you use to pump air through the radiator....mechanical or electric...., it will absorb power from the engine. Directly from the mechanical fan; extra effort from the alternator (it's driven by the engine, too) if you have electric fans. The energy consumed is about the same; weight, etc could be different. But, no method comes "free".
Whatever method you use to pump air through the radiator....mechanical or electric...., it will absorb power from the engine. Directly from the mechanical fan; extra effort from the alternator (it's driven by the engine, too) if you have electric fans. The energy consumed is about the same; weight, etc could be different. But, no method comes "free".
Spot on. There's rarely, if ever, a free lunch in life.
Whatever method you use to pump air through the radiator....mechanical or electric...., it will absorb power from the engine. Directly from the mechanical fan; extra effort from the alternator (it's driven by the engine, too) if you have electric fans. The energy consumed is about the same; weight, etc could be different. But, no method comes "free".
Not even close.... First off, the electric fan only runs part of the time, as opposed to the clutch fan running all the time. Going down the road, most of the time my E fan isn't even running and I'm cruising at 180-185*…. where as a mechanical fan would be eating some power..
Lastly, the load on the alternator is definitely increased when the E fan is on, it pulls my idle down about 50 rpms, but its no where near what a clutch pulls for power. I've raced my car extensively and even left the fan on by mistake, it loses .5 mph on average.... Where as the clutch fan killed 1.5-2 mph on average...
I bet the alternator doesn't take more the 3-4 hp to run at full load....I may test this eventually on the chasis dyno next time I'm on it.. The best thing about the E fan is, it doesn't run when it doesn't need to....and when it is running, its cooling much better.
We all have our "beliefs". Some beliefs are actually based on reality; others are just what we wish them to be. Whether a mechanical fan or the electric version will be most efficient for a specific vehicle is more a function of the selection of temperature settings (thermo trip-point or e-temp controller settings) and the actual "needs" of the cooling system. The actual energy used for either is not as much different as you think. The mechanical fan runs all the time (mostly in "slip" mode)...but it is always pulling cool air through the radiator, too. The e-fan runs only when controller calls for it, but it sees larger swings in temp and works harder....when it works.
Bottom line: If both systems keep a running engine managed to the same average temperature, the amount of cooling air going thru the radiator MUST be about the same. Thus, the work done by either must be very similar. To the engine, work is work, whether it is done by the alternator (via fan belt) or by the water pump shaft (via a different belt).
It's not a magical mistaken belief. Electric fans will use less HP when running. Supplying 60A of current o electric fans requires under 1HP at all rpm's while a mechanical can easily be using 20-30 HP at the higher rpm's. I'll dig up the links to a couple of sites with test data that prove this tomorrow.
There's a simple reason why electric fans can use much use less power. They always run at their most efficient speed.
Last edited by lionelhutz; 07-03-2018 at 01:04 AM.
20 hp at what rpm? When idling at 700 rpm? (20 hp is probably more than an unloaded engine generates at idle.) When cruising at 1500 rpm? Or only when you wind it up to engine redline? Clutched thermo fans use considerably less energy than fixed-blade fans. Rotating mass is the biggest drawback for a thermo fan.
I can see if the clutch is locked up sure it will suck some power up, you can feel it.
Thing is if youre not racing it does it matter? Is it worth baking your engine?
Only thing about electrics I dont like is
1) if it fails youre stuck
2) a 2200 cfm 16 spal fan moves lots less air than a stock mechanical fan its night and day difference. With an electric you may have a temp fluctuation which I dont care for. Nitpicky stuff
They ea have their + and -. Ideally either get a dual elec fan setup, or a mechanical with an electric as an auxiliary.
Cant have enough cooling system imo.
If I had to do it over Id stick the plastic fan back on and use the spal on a thermostatic setup
Many yrs ago used to see guys run a clutch fan with a white plastic fan blade
1) Installing the clutch-fan with the electric still on the back of the radiator only restricts airflow a bit (for the e-fan footprint). So that will work OK as it is.
2) Yes. Your biggest issue was not having a full-width shroud on the radiator feeding ONLY the elect fan. With your setup, you could just install a plate over the output of the existing shroud, cut a hole for the e-fan, and mount it. Voila'....full-shrouded radiator with your e-fan doing the WHOLE job. [Sealing the areas of air leakage will improve cooling efficiency some.]
It's your choice what you want to do. You can go with option 2, if you want to go electric. If you do that, the 'turn on' temp for your controller should be around 200*F; the "turn off" temp should be about 170-180*F. If you go back to option 1, just remove the e-fan from the radiator.
With what you already have, I would probably go with Option 2 and controller adjustments, if they are much different than what I suggested.
06-30-2018, 11:32 PM
