I currently don't have any issues with my cooling system but I have sometimes wondered if I should get a fan clutch.

If it ain't broke don't fix it

Ed

 

I sure does eat the HP without the clutch. A stock type steel fan with no clutch, like -30hp. but if your not worried about it, it works so keep cruising.

 

While I share the overall thought about Ed's statement above if the fan noise doesn't bother you leave it alone. Yes you may get better hp while it is not engaged and overall mileage will go up a bit. Usually clutch fans were used with high performance or AC cars with the usage of higher pitched larger diameter blades for maximum cooling that do make more noise overall. The clutch lets them spin slower until needed reducing noise..

 

Quieter, more HP as it is less drag on motor....why not?

Standard duty clutch fan would be fine considering you have no cooling issue currently. You just need to get the right bolt pattern clutch for your fan.

 

I ended up switching from Std Duty to Severe Duty Fan Clutch because of overheating.

Flex fans are noisy obnoxious monsters. I dig my fan clutch.

 

I would not open that can of worms....as above... if it's working, why mess with it ?

 

It sounds like you have a solution looking for a problem.

 

Some, including me, would suggest the "problem" existing currently is more noise, especially during Hwy driving, and more engine load (= less gas milage) and loss of HP. not using a fan clutch

Agree on the point OP has no "cooling" issue.....but in the bigger picture a clutch fan would be beneficial.

 

OP sig notes 427 SBC....a HD clutch fan would engage fully at a lower engine temp vs standard duty which given his CI may be the direction to go. Typically HD clutch fans were used on AC cars as they have the condenser to also pull air through.

The only other consideration the OP might take beyond fan clutch is get a 7 blade 18" fan.

While driving at speed, especially Hwy speeds, the airflow through the radiator is doing the heavy lifting relative to engine cooling which is where a clutch fan relaxes more taking strain off the engine. Less fan noise and likely a small bump in MPG.

 

OP sig notes 427 SBC....a HD clutch fan would engage fully at a lower engine temp vs standard duty which given his CI may be the direction to go. Typically HD clutch fans were used on AC cars as they have the condenser to also pull air through.

The only other consideration the OP might take beyond fan clutch is get a 7 blade 18" fan.

While driving at speed, especially Hwy speeds, the airflow through the radiator is doing the heavy lifting relative to engine cooling which is where a clutch fan relaxes more taking strain off the engine. Less fan noise and likely a small bump in MPG.

I am running SD clutches on both my 400hp 355 71 SS and my 68 high compression L79 331 and both have AC. I am in the NE but haven't had any overheating issues however the L79 does have a nice 1.25 inch X2 Cold Case. Maybe I should switch to HD clutches especially with out recent temperatures.

 

At slow speeds and low rpm the clutch fan will move the same amount of air as a fixed fan.
At faster speeds and higher rpm I’m may not move as much but at higher speeds like over 30 mph it doesn’t matter. So imo the clutch fan is a win win and should not impact cooling at all.

 

I spoke with Hayden and at low speeds the Standard Duty clutch is only about 20% engaged during low heat operations. HD is about 30% at the same point and max is around 75-80 SD and 90% fully engaged HD. They never truly lock up either.

 

Here is a decent short read on the subject. I think I will definitely go to a HD

FAQ - Fan Clutches

www.haydenauto.com

 

I have EDIT: heavy duty fan clutch, 18" x 7 blade fan and CC 23" radiator in front of my 411hp 355. Here in SoCal it gets over 100 degrees in summer. Even stuck in stop and go traffic for 30 min, no cooling issues but I also don't have AC

I do however have a HD water pump

 

I have standard duty fan clutch, 18" x 7 blade fan and CC 23" radiator in front of my 411hp 355. Here in SoCal it gets over 100 degrees in summer. Even stuck in stop and go traffic for 30 min, no cooling issues but I also don't have AC

I do however have a HD water pump

Obviously pitch on the blades really comes into play between SD and HD or even Severe Duty. In your case you are using the HD cooling radiator with a greater cooling surface that helps compensates for a less effective clutch. 100f degree stuck on a highway with no AC, no thank you sir.....Ugh!

 

Some 411 on different aspects of standard vs heavy vs severe duty fan clutches and the fan blade pitches relative to each

4s410-fan-clutches-standard-heavy-severe.pdf

 

Not to over kill this topic but here is a better link that talks about initial engagement and max with the SD,HD and Severe duty. I promise no more links

Thermal

www.haydenauto.com

 

I was having overheating issues in traffic with the stock 4 blade fan. I Purchased this 18 inch 7 blade fan from Pick-N-Pull for less than $15. It's from a 1979 Cadillac DeVille. The pitch is very aggressive and it really moves the air when the Hayden HD clutch engages. The part number on the clutch is 2747.

A HD clutch is necessary with this fan.

Here is a comparison of the Cadillac clutch fan with two aftermarket fans with less pitch. Which of these three fans would you want when stuck in traffic on a hot day?

I installed AC in a 1956 Chevy which caused a preexisting overheating problem to get worse. Installing a clutch fan from a 1978 Cadillac Seville 100% cured the overheating problem this car was having.

I am currently working on installing a BBC in another 1956 Chevy and it will also be using a Cadillac 7 blade fan.

 

Some fans have some relatively low RPM limits on them. On a high revving engine the lower fan speed with a clutch fan reduce the risk of tossing a fan blade through the hood.

 

6 blade mechanical HD Derale fan. standard aluminum water pump. 160 stat. full shroud. top and bottom filler panels. cools my 11-1, 540 horse to 175 all day long. the hottest i ever seen it with this setup is 185 sitting in traffic with an ambient temperature of 95 for 12 minutes

 

Thanks for the replies. I think I will go ahead and try a fan clutch. I can always switch back if needed. Looking at the Summit questions and answers I should get a standard duty clutch ( 2705) based on my fan pitch. It says for a pitch 2 1/2 in and greater use the HD clutch. Less than 2 1/2 in use the standard. My pitch is about 2 in.

 

I may have spoken too soon. I may need a different fan also. My current fan just has 4 slot holes for the bolts and a small center hole to fit on the spacer. I guess if I get a clutch I need a fan with a large center hole?

 

Yes you need a fan for a fan clutch. Need to match the center hole size and bolt pattern to a corresponding fan.

My 5 blade fan clutch did not bolt up to my new 7 blade fan so I had to get a fan clutch for the 7 blade

specs of hole size typically are provided in description of fan and fan clutch

 

How about a twist?

My ZZ4 is a reverse-rotation motor. Talk about a headache to find a fan/clutch combo that works!

Solution:

• Replacement Cooing Fan is Dorman 612-108 455mm (18") Dia., 5-blade, Reverse Rotation
• Replacement Fan Clutch was a Hayden 2734 Heavy-Duty, Reverse Rotation - I step drilled the female pilot to 0.750"dia. X 0.125" deep. Later replaced with a Hayden 2785 Severe-Duty as it has the .750" pilot hole.

 

How about a twist?

My ZZ4 is a reverse-rotation motor. Talk about a headache to find a fan/clutch combo that works!

Solution:

• Replacement Cooing Fan is Dorman 612-108 455mm (18") Dia., 5-blade, Reverse Rotation
• Replacement Fan Clutch was a Hayden 2734 Heavy-Duty, Reverse Rotation - I step drilled the female pilot to 0.750"dia. X 0.125" deep. Later replaced with a Hayden 2785 Severe-Duty as it has the .750" pilot hole.

• View attachment 308499

I used that same fan but had bad luck with some clutches. The best CCW clutch imho is this.
It's a little pricey.
More Information for GM GENUINE 1540109 (rockauto.com)