5-Blade VS. 7-Blade Viscous Clutch Fans

[Moparman01]

Simple, is the 7-Blade viscous fan better (more air flow) that the 5-blade version? Between my father and i we have 3 cars with the 7-blade viscous clutch fans, one a 440 Cuda, a 383 67 Charger and my '71 Demon 340. None of them over heat, ever! I want to add on to my 69 440 powered Charger. I have brand new "Jaguar" clutch unit but i only have a 5-blade viscous fan. I can't find anywhere that re-pops the 7-blade, and old ones that are for sale are well over a $100 bucks!! I was thinking since my Demon runs very cool i might swap out the 7-blade from it and put in the 5-blade, and use the 7-blade for my Charger. Just wondering if there is really that much of a difference in over air flow and cooling potential between 5 and 7 blades, i don't want my Demon to start have overheating issues if i swap out the blades. Thanks! 

[Kern Dog]

I have wondered this too. The OEM HD cooling package included the 7 blade with the fan clutch, a shroud and the overflow bottle/jug. It seems to me that they used a 7 blade unit for additional airflow. The newer "Magnum" 5.2 and 5.9 engines used an even bigger fan so my guess is that more blades equals more flow.

[cdr]

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[myk]

The suspense is killing me!

[John_Kunkel]

What's more important, the fan diameter, the number of blades or the pitch of the blades?

[c00nhunterjoe]

I think the shroud is more important then the fan.....

[A383Wing]

I think the shroud is more important then the fan.....

if that was the case, then every car made would have had a shroud on them, which they don't

this is the blade I'm running on my cars, it really moves some air, and no shroud on one of my cars

http://www.ebay.com/itm/350991444070?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

[garner7555]

What's more important, the fan diameter, the number of blades or the pitch of the blades?

Good question.  Haha   My    would be a mixture of all 3.  Large diameter, with good blade pitch, and ample amount of blades.  (I think 5 or 7 blades would both be enough for normal application)  

I also agree with Coonhunter, the shroud is EXTREMELY important.  Without a shoud a lot of the air you're pulling doesn't go through the radiator.  

[c00nhunterjoe]

I think the shroud is more important then the fan.....

if that was the case, then every car made would have had a shroud on them, which they don't

this is the blade I'm running on my cars, it really moves some air, and no shroud on one of my cars

http://www.ebay.com/itm/350991444070?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Show me 1 car made today that does not have a shroud on it. I will even expand that to any car made since the 80s... or even 70s. All have shrouds, and elec fans have them built into them. The size of the fan means nothing if it is not pulling air through the radiator.

[303 Mopar]

Show me 1 car made today that does not have a shroud on it. I will even expand that to any car made since the 80s... or even 70s. All have shrouds, and elec fans have them built into them. The size of the fan means nothing if it is not pulling air through the radiator.

What fan are you running?

[ACUDANUT]

I think the shroud is more important then the fan.....

A 3 row rad. with a viscous fan package has made the shroud use (not needed) imo

[John_Kunkel]

What's more important, the fan diameter, the number of blades or the pitch of the blades?

Good question.  Haha   My    would be a mixture of all 3.  Large diameter, with good blade pitch, and ample amount of blades.  (I think 5 or 7 blades would both be enough for normal application)  

 

The point is, a steep pitch will move more air for a given diameter but there is a point where the pitch is so steep that the belt will slip trying to turn it at higher rpm's AMHIK...that's why a clutch fan can move more air than a rigid fan of the same diameter.

[A383Wing]

Show me 1 car made today that does not have a shroud on it. I will even expand that to any car made since the 80s... or even 70s. All have shrouds, and elec fans have them built into them. The size of the fan means nothing if it is not pulling air through the radiator.

My 70 Charger never had a shroud on it from the factory, so your statement has just been proven wrong

I also have a 1988 Dodge Shadow with 2.5 engine, factory AC, and electric fan, no shroud on that car either....

[will]

   The pitch can get to the point where there is an extreme dropoff in efficiency and a corresponding increase in load on the driver. They compensate this by adding blades to the fan. More blades, more air flow. A gas turbine has more blades with each successive stage, thus compressing the air to the point where the engine makes more air than it could ever use for combustion.
   They used various fans for cooling. I think the 7 blade was for max airflow for cooling, don't forget you need quite a bit of airflow for the A/C condenser. You need to change the refrigerant in the condenser from a gas to a liquid to cool the occupants.

[A383Wing]

which is why with the clutch fan set up, whether it be thermostatic or non-thermal clutch fan, if there are more blades and the pitch of the blade is great, then it will move a lot of air through the radiator at low speed, and then when the car is moving fast enough to cool the radiator while moving, the fan will basically be neutral and not hinder the air flow while moving

[c00nhunterjoe]

Show me 1 car made today that does not have a shroud on it. I will even expand that to any car made since the 80s... or even 70s. All have shrouds, and elec fans have them built into them. The size of the fan means nothing if it is not pulling air through the radiator.

My 70 Charger never had a shroud on it from the factory, so your statement has just been proven wrong

I also have a 1988 Dodge Shadow with 2.5 engine, factory AC, and electric fan, no shroud on that car either....

You missed the point. 99.99% of the cars have shrouds or some design to channel the air from the fan through the radiator. The electric fans, like what are found on your shadow, are direct mounted to the radiator thus eliminating the need for a physical shroud since a direct mount doesnt need to channel air. The purpose is to move the air across the fins. On a mechanical fan system, it the blades are close enough then a should is not needed in many cases, but at the same time, when the fan is that close, you risk contact and that has been seen on this site many times before. When the fan is roughly more then an inch away from the rad, a shroud should be used to keep the air flowing through the rad instead of turbulance under the hood.
    The cardboard test is a good backyard measuring device to test airflow at idle.

[John_Kunkel]

The shroud helps efficiency in marginal cooling systems but a lot of older cars with no shroud will never exceed the thermostat temperature. You can't compare them to modern cars that purposely run insanely high coolant temps to comply with emissions regs. 

[A383Wing]

You missed the point. 99.99% of the cars have shrouds or some design to channel the air from the fan through the radiator.

bet if you take a poll of the cars on this site, you will find that statement to be false also....I bet most of our cars here on the forum never had fan shrouds from the factory, unless they were AC cars

The shroud helps efficiency in marginal cooling systems but a lot of older cars with no shroud will never exceed the thermostat temperature. You can't compare them to modern cars that purposely run insanely high coolant temps to comply with emissions regs. 

and those modern cars usually have a one core radiator that is barely adequate for cooling a lawn mower engine....our cars have much bigger radiators

[ws23rt]

Hmm.

Air flow through the fins equals cooling. --- As I recall when driving my cars (back in the day )  Moving through the atmosphere gave the flow needed when the engine was working (making heat).  At idle not much heat was produced.---Engineers did the math and all was well.

I had no overheating issues that come to mind that were related to the original design with any of my many old cars.

I do remember a time for the need to block my radiator with cardboard in my 68 hemi RR just so I could keep warm myself inside the car. Also when driving in 90+ degree heat in that same car (btw no shroud)  overheating was not an issue.  The same goes for my 70 charger rt with AC.

So what is the big deal today??   Air flow and heat exchange are things that have not changed. -- Something has changed or we would not be talking about this so much.

The original question about the number of blades on a fan seems more a question about originality.  The pitch of the blades has something to do with air flow so it is a good question about which moves more air.   However if seven blades did pull more air it would take more horsepower to do so. Which equals more heat being generated.

[Mike DC]

 
Lots of unrestored survivors in this hobby have shrouds.

Lots of modified cars have no shrouds - and either aftermarket rads or owners who complain about overheating.


Hmmm . . .   

[Moparman01]

Didn't know this would get to be a pretty serious discussion, but some good info none the less! Well, i've never had a viscous clutch fan on my Charger, the radiator i had in the car would not allow enough clearance for the fan clutch (yes not even the "Jaguar" clutch, we are talking less than a 1/4 inch!). I've struggled with this car over heating (230*+) for quite a few years now. Last year i put in a brand new Griffin 26" aluminum radiator and still had over heating issues at idle. But, unlike my old radiator, the new radiator mounting flanges are flush with the core so i realized it had plenty of room for the fan clutch to fit with out being way to close to the radiator! So this weekend i finally put the 7-blade clutch fan into the car, took it out for a ride, and for the first time since the 318 came out of the car in favor of the 440, the car did not over heat!!! As much as i let it idle it never exceeded the 180*'s, which it's NEVER done before! It was only in the low 60's today so i'm not sure how it will behave when it's in the 80's-90's over the summer, but i have had it over heat in 50* weather in the past. I have to admit i was bit skeptical (and maybe still am) but maybe there is something to the viscous clutch fan set-up. And, yes, i also do run a fan shroud.   

[myk]

Hmm.

Air flow through the fins equals cooling. --- As I recall when driving my cars (back in the day )  Moving through the atmosphere gave the flow needed when the engine was working (making heat).  At idle not much heat was produced.---Engineers did the math and all was well.

I had no overheating issues that come to mind that were related to the original design with any of my many old cars.

I do remember a time for the need to block my radiator with cardboard in my 68 hemi RR just so I could keep warm myself inside the car. Also when driving in 90+ degree heat in that same car (btw no shroud)  overheating was not an issue.  The same goes for my 70 charger rt with AC.

So what is the big deal today??   Air flow and heat exchange are things that have not changed. -- Something has changed or we would not be talking about this so much.

The original question about the number of blades on a fan seems more a question about originality.  The pitch of the blades has something to do with air flow so it is a good question about which moves more air.   However if seven blades did pull more air it would take more horsepower to do so. Which equals more heat being generated.

Low octane fuels and the resultant highly  retarded timing settings are to blame, right?

[Nacho-RT74]

All that I know is:

AC cars got 7 fan blade, HD thermal viscous fan clutch, small pulley and 6 blades water pump ( although I haven't seen 73 and lates 6 blades water pump but 8s )

Non AC Cars got 5 blades fan on a regular thermal fan clutch, bigger pulley and 8 blades water pump.

[c00nhunterjoe]

Search this site for overheats and runs hot topics. Majority of them come down to not running shrouds, despite their choice of 5 or 7 blade fans. Sure, it might have been enough when they were bone stock. But how many of them are still like that now?  Strokers, compression, big cams, garbage fuel. How many of these cars have the better fans, aluminium radiators, and still run hot in traffic withiut a shroud? Every summer the new topics regarding overheating roll in and i have yet to see where simply swapping to a 7 blade fan is the magic fix.

[ws23rt]

^^