Kid Vette

OK, I'm going to show my ignorance. Exactly what are the advantages of a flex fan over a clutch fan. Is it less wight, require less HP, more CFM or all of the above? And if flex fans are better, why didn't GM ever stick them on the Vettes? Or aren't flex fans better? :confused:

I need to replace my clutch fan (its bent) and don't know whether to get a new clutch fan or go to a flex fan. I know a lot of people will say just go with electric fans but I don't want spend the time or money it would take along with installing a high output alternator to drive them.

Are there any magazine articles that do a comparison? I don't want to base my decision just on what all the advertisements say.

Smokehouse69

In my opinion no. I think you answered your own question Why did no car builder put them on cars? Because they aren't better, simpler yes, but better, no. Personally I don't think much of mechanical fans at all, and think that electric fans are the way to go.

Pete79L82

All I can give you is first hand dyno experience.

Clutch fan:
Pros: 2HP loss over no fan blade when clutch is disangaged. Hp loss with cluch engaged veries greatly with type of fan used. Better throttle response over a flex fan.
Cons: Does not like to be turn at high RPM. Always some clutch slippage, so will not flow as much CFM as a non-clutch fan. Clutch is expensive compared to a flex fan and spacer.


Flex fan:
Pros: Can be turned to higher RPM safely. Many choices of size and pitch to match your CFM reqirements.
Cons: Huge HP lose. Best flex fan I have found to use is a Derale 15" plastic fan, which has a 19 HP loss over no fan. Best metal flex fan I have found is a MR Gasket 15" , which has a 26 HP loss over no fan.

You will have to decide which features fits your requirements best.

Armstrong

When i bought mine it had a flexfan on it.
It works fine and cools great but i'm sure there is horsepower lost.
I plan on going to an electric setup someday but for now this is fine.
Other areas are recieving my attention at the moment.

No Ignorance shown on my opinion :cheers:


[Modified by Armstrong, 6:43 AM 9/7/2003]

Larry B.

You will have a lot more noise from a flex fan. I have seen flex fans come apart at high rpm.. There are two types of clutch fans: temperature (thermal) controlled and centrifical. You can adjust both types clutch fans to dis-engage at different points if you need more cooling. Electric fans take power too... It loads the alternator... You can't get something for nothing.


[Modified by bluevetteman, 6:50 AM 9/7/2003]

bigvette1

Pete79L82 - How did you come up with those figures? They are large.

3 options - stock fan and clutch ok, but may not pull enough air at idle and slow traffic, overheating.

flex fan - pulls large amts of air at idle and slow traffic, better cooling.

electic fans - pull air when needed at large volums. Drawback loss of stock look and about $300 for a good set.

jerryp58

"Hp loss with cluch engaged veries greatly with type of fan used"

Do you have a min and max for the clutch fan engaged to compare with the 19/26 HP loss for a flex?

Pete79L82

Bigvette1:
I came up with those figures buy running test on here.



When you do your own dyno testing you quickly learn the truth about what products work and which do not, instead of the distorted reality of advertising and advertising paid magazine articals. When I was testing fans I found some 17" and 18" flex fans that took as much as 40 HP away over no fan. I stress again thaqt these numbers are compared to NO fan.


Jerryp58:

I tested 6 different clutch hubs and 8 different fans in various combinations with over 200 dyno pulls. After a lot of head scratching I was not able to come up with a definate conclusion. When you do intensive dyno testing you have to get repeatable test in order to draw a conclusion. I like to strive for 2/10 of 1% repeatability. I could not get any where near this testing a fan clutch. One of the problems I had was trying to get the clutch to lock up. Because of the large amount of air movement in a dyno room I could not get enough hot air directed to the clutch to get them to lock-up on a consistent basis. By monitoring fan speed vs pully speed I realised that I could not get the clutch to lock up completely. The only thing I can say is that none of the clutch fan combinations loss more than 9 HP on any of the tests. How this relates to actual on-road conditions I don't know and don't want to draw any conclusions from. I do beleive that this would be a better test to run on a chassis dyno than an engine dyno.

Matt Gruber

as far as i can tell, fan tests are best at the drags or with a g-tech.
a stationary test is misleading because airflow at speed is ignored.
i've done some tests with motors/fans and the power to drive a fan decreases due to "ram air".
Off the line there is usually plenty of power(not always) so fan loss may not matter. certainly by 50-60mph fan loss gets smaller, LOTS smaller. Probably at 80 and up there is little loss: BUT this depends on the design of the car, so a test in say my 61 won't necessarily transfer exactly to my 72, for example.
The easiest test anyone can do is NO FAN vs. whatever, in the 1/4 mile. then use charts to compute hp loss, i am sure there is SOME, but not as much as on a dyno. :cheers:

MotorHead

How do you adjust a factory clutch fan ?

Matt Gruber

here is an experiment anyone can try.
on a breezy day, put a 20" house fan outside.
DO NOT PLUG IT IN
when a breeze hits it watch how fast it spins.
now imagine the wind thru the car radiator at speed.
fans take less engine power than you may think

Pete79L82

Now take that same fan and put a radiator in front of it and watch it stop spinning.
From experieance, not theory, I can tell you that a fan take a LOT of horsepower. Taking a fan blade off the engine will always lower lap times on a race track.

Pete

Matt Gruber

fans do take hp :cheers:
i don't think it 40 HP.
can these skinny belts handle 40 HP? day in day out? (i don't know, i'm just wondering)
But i hope you are right Pete, i'll pick up a few MPH at the drags. :cheers:

Pete79L82

Matt:

Instead of going to the drags, take a ride west on 44 to New Smyrna Speedway and see if you can even find an engine mounted fan on any of the top race cars. :steering:

Pete


[Modified by Pete79L82, 6:45 PM 9/7/2003]

Kid Vette

Thanks for all the input! I think I'm going to stick with a clutch fan. I'm sure electric fans are better but I'm trying to keep my car somewhat stock and I really don't think $300+ for a few HP is worth it.

I think I will start with a 5 blade fan that was used on non-AC cars and go from there. I can go up to a 7 blade fan if it turns out I need it. Somebody said something about adjusting the clutch. How?

So. . . any of you guys with electric or flex fans want to get rid of your old 5 blade clutch fan? I checked the Corvette Parts Interchange Manual and it says the same one was used from 1972-1979. Part number is 3991420.


[Modified by Kid Vette, 7:05 PM 9/8/2003]

71coupe

Ecklers sells a replacement fan for clutch type fans thats made from aluminum. (not that weight is much an issue as drag)
Also, PAW sells a non-thermo clutch that decouples at higher rpm levels. If it uses flyweights, I think it would be adjustable with lighter or heaver springs.

IMO you can't beat the reliability of an engine driven fan. Electric fans make a good supplement fan, but not by itself.

stpman

I don't know about that, I had an 86 Firebird that I drove for 8 months before I found out the fans (electric) weren't connected. it didn't overheat until I left it sitting while I ran into pick up some forms from the doctors office (friend sitting in the car). as long as the car was moving it was fine.

Steve :steering:


[Modified by stpman, 9:34 PM 9/8/2003]

Matt Gruber

when i was going to college in NJ i used to remove the fan all winter to get faster warm ups. They were direct drive fans, no flex, no clutch, on darts and valients. as i recall the cars were about 125 HP. Now, if the fans drew 40 HP, wouldn't i have noticed a big power increase? But i didn't.
Yes, i kept them off 8 months of the year.
.
Having an electric fan that is not connected proves that they are less reliable. They would not work if needed.

PRNDL

OK, I guess I will have to run a realworld test. I have a flex fan. The original clutch fan is long gone. Next time I am at the dragstrip I will just cut off the fan belt right before I stage. Then we will see if I improve my best mph! Then.... I wll call AAA and go home on a rollback! :lol: Unless I can figure out how to reinstall a new fan belt. :) MJ

Matt Gruber

Close :lol:
next time loosen the belt just enough so it slips. might have to experiment to get the "sweet" spot.
this will get gains from the water pump too, so it could be more dramatic!
just watch that temp gauge!