No, I have read those two footnotes and the fan/viscous data is from a Society of Automotive Engineers (SAE) on the then new 340 V8.
Some of the generator shaded area in the graph showing variation is from a SBC 350

You'd think the SAE would know the difference between a 5.6 and a 5.7l engine. Of course one wonders where they found a 350 with a generator since they started using an alternator in 65 and the 350 came out in 67. Basic mistakes like that makes you doubt the data.

As long as you stay moving Sniper. My electric fan never runs.

Clutch or not to clutch.

Just how much gain is there to be had by a clutch?
Are you running pro stock where every last horse power needs to be there?


For me, a failing fan clutch is one less thing I have to worry about failing down the road. Be it a torgue drive or temp controlled IMO makes no difference. Sooner or later it will fail.

Ive heard the argument a direct drive fan is noisier , I'll call BS to that . Mine inst loud at all and I assure you I can not hear it windows open or closed, I surely cant hear it going down the road

what controller did you use ? TIA.

Always room for one more opinion. Even when that opinion is the complete opposite of all the other posters.

So,,,,,,Just how much is to be gained by adding a clutch fan over a direct drive fan ? Anyone done a side by comparison

is the blade pitch any different between the 2 styles of fans
The diam and blade count is the same. Then makes since the only gain is horsepower. So whats the side by side comparison ?

Other than keeping original is there any good reason not to do an electric? If your rad and cooling system is up to par the electric should never kick on unless you're sitting in traffic.

It is not a big deal nor is it worth arguing about. Virtually all OE manufacturers went to the clutch fan as they became available and cost effective. Especially our Mopars. If you want to live in the pre-68 +/- era, that is your prerogative. For the rest of us, post '68 with a clutch fan or post '85 +/- electric fan is the way to go.

Your opinion goes against 50+ years of experience for the OEs and most posters here. And you are welcome to it.

There are no simple answers to your question as the size, pitch and number of blades all come into the equation. Normally a Clutch fan will have a more aggressive draw when engaged than a non clutch version but only drains the power when it's needed. The non clutched version on the other hand is a constant drain on the output of the motor whether it's needed or not.

I believe when people say a direct drive is noisier they are likely referring to an aftermarket flex fan some which can be very noisy.
If I remember correctly articles in the past have claimed a 7-10 hp difference on a healthy V8

A post over at A bodies only claims a 15 HP difference was verified on a dyno, I'd like to see the article as the only way to confirm that is if they used the same exact fan w and w/o a clutch and repeated the test several times
LINK TO A BODIES POST

Some of the 18 wheel trucks now use fan clutches that you can engage or disengage electrically.
I would not mind trying one of those.

I liked my experiments running without any radiator fan,
except the one time I hit a near traffic stall on an Atlanta ring road
during hot weather when I wanted the AC to have airflow while barely inching along.

Try running that big 7 blade fan without a clutch at 6000 rpm or more. You will be wasting 40 horsepower if the belt stays on. A fan clutch is the next best thing to electric. Better than a flex fan. On some cars, electric look/sounds too stupid, so you need mechanical.

I tried the electrically engaged Horton on my '96 Diesel Dually, I saw NO gains at all. When engaged it was NOISY. Later I got an FL-60 w/ Cat 3126, 250hp with a viscous thermostatically controlled fan. I went back to stock and sold the Horton. I'd like to try the Mercedes electric setup but don't really want to upgrade my '60's electrical system to deal with it.

Mack has had that since at least 1980. I would turn the fan on when going down hill and use it for braking and max cooling then over-ride the fan and shut it off when climbing the other side. Yes, I said "braking": that's how much power that fan is making when it's locked up. Speaking of brakes, if the water temp was too much and you still had hill left to climb and had to switch the fan back on, it was like tapping the brake.

I took my fans off all my Rams. One has an electric and I never use it. But, I don't have gridlock to deal with either.

Carry on with your debate about clutch vs solid...........I'll stick with my electric or no fan at all. Less water pumps to replace too because that heavy turd is not beating on that little bicycle bearing that's in the water pump (which fails every time)


And Joel, yes, I agree with you the electric fan looks stupid on a vintage car, especially to folks like you and I that appreciate a stock appearance. But the benefits out-weigh the esthetics. Hide it inside the rad shroud, that's what I do.

I ran the Mercedes fan on a blown Hemi A body I built a few years ago. There was no room for any kind of mechanical fan. It did a great job of cooling. I would have one on my Cuda today, but the clutch fan does a good job and I like the period correct look.

The only down side with the clutch fan was when I ran the KOS races at the local track. It was tough to keep the engine as cool as I wanted while sitting in the staging lanes when we hot lapped. No overheat issues, just wanted the engine cooler at the line.

Agreed, I've run nothing but 5-7 blade fixed fans for decades on my toys, no complaints, then again for those that can hear their fan over their exhaust note, then their not driving a real "musclecar" in the first place....

Who would have thought you could this much discussion over a fan?

Well it has been raging for many years and there is no definitive answer.

Form over function, stock or custom, how hot is too hot?
Most cars and trucks work well ‘most of the time’ with any fan type.

The poo hits the fan when it’s a hot windless day and you hit a JAM!
I haven’t daily driven a Mopar for many a year, but I have friends who do.
One uses an Ali rad with an electric fan and the other has an original rad and clutch fan.
Both live in around the biggest car park in Europe called the M25 motorway...

Well on the whole, they both do OK most of the time...

Once the engine gets really hot, it’s real hard to get the heat back out with an all iron engine...

The one thing about the Mopar thermostat controlled clutch fan is how they say it will give more HP. Thats true when the fan is not kicked in but when the car is hot the fan will kick in until you pick up enough speed to get enough air through the rad. I know I remember my 83 Ramcharger with a 318 and clutch fan and AC would engage when I sat at a redlite for a minute or two in 80 plus temps. Then when I took off and got to third gear it sounded like it was still stuck in first or second as the fan was screaming. After about a mile at 65 mph it would disengage and then you did not hear it. And they work fine on the street but for a street strip I think the RPM style clutch fan may work best as it just slips more as the rpm goes up. I always thought if I was racing my car and had to wait for someone at the line and my car hit 180 or more the clutch fan may kick in and rob some HP when I take off. Course I dont know how much it would kill in HP but it seems the RPM would work best for that. Ron

It is all about trail and error. If you are a car show groupie then run a clutch and you can not hear it when the car is shut off. I have run and electric water pump drive on my motor on the street cooled ok but was a better choice for the track. Right now I run a 26 inch nice clean factory rad, mated water pump and housing rad has the shroud.I do not run a clutch on my factory 7 blade fan. I also have a hi flow thermostate 160. It is a 430 ci Hemi and it is more than stock and see a lot of RPM. Mech. gauge shows 163 degrees.I have driven it in 90 plus degrees and it still runs 163. I can see on the gauge move when the 160 opens up. These clutch fans have some noise to them so you might have to live with it. I have seen more than one fan come apart at the track so High RPM might not be a good thing for the factory clutch. Your choice of what you use, some times there is no answer to your question until you play with parts.

With a clutch fan, I run the lighter weight aluminum 7-blade fan.... saves a little weight from the common steel blade fans that are with most clutch fans.