Fan Clutch

my stage 2 465 has a romac balancer. that moved the fan about 1/2" further into the shroud. the fan blades are about even with the end of the shroud. runs cooler than the 430 ever did. has another point and a half of compression too. so, take it with a grain of salt.

 

GM part number?

All you've told me is that the new engine--and perhaps the new water pump--is more efficient than the old one. The fan is not more effective, if it's been buried too far into the shroud.

 

It's not rendered useless either as some are implying. i would not invest hours and money moving a fan back or forth 3/4 of an inch. it simply isn't that big of a deal.

 

SAE scientific studies demonstrate the amount of air moved through a fan shroud is very sensitive to small changes to the projection of the fan into the shroud.

"This clearly shows that the fan performance decreases for to small FpiS. Judging from Figure 24 maximum massflow is obtained somewhere between 55 % and 60 % FpiS.”

FPiS = Fan projection into the shroud.

See the graph in Figure 24 here:
http://mechcomp.com/webpage-mtrl/documents/2008-01-1171.pdf

The SAE fan position cooling studies date back at least to 1913 at which time they made a 50% projection recommendation for optimal cooling. Since then additional studies have varied in the 50-66% range depending on the configuration. If you look at the parabolic shape of the curve in Figure 24, the inescapable conclusion is that small changes from the optimal cooling position of the fan relative to the shroud do make a lot of difference.

 

What are you getting at here? You returned a clutch, you tossed a clutch you asked for a recommended part number and now you say it's not a big deal....

 

I wasn't looking for any recommendations. I warned the OP about my experience with the HD clutch. i tossed that clutch because it never disengaged, not because the fan wasn't oriented properly in the shroud. I didn't even think to compare the depth difference between the two clutches. I think you misinterpreted my post.

I'm not doubting or disputing that the fan should stick out of the shroud 1/2 way to maximize it's efficiency. I'm saying with it too far in it is still more than adequate to cool my 11:1 465. so I wouldn't tear your hair out moving the fan around. as long as its about where it's supposed to be its probably fine.

 

i can't seem to copy and paste of that article. cool read. according to the data there is only a 2% decrease in airflow between 66% in the shroud vs only 33% in. with that data i certainly wouldn't stress about fan orientation on the shroud. close enough is fine at 2%

 

Question for you guys. On a hot day with car running at around 180 degrees. Shut off engine and you can spin fan freely. Should there be some resistance? had this fan clutch set up fort the last three years or so with no overheating until idling in a parade last summer. Got up to about 220 degrees before it shut if off. Just think the fan clutch may be shot.

 

Modern fan clutches need to see something like 170 degree air coming off the radiator before they'll engage. The coolant temperature must be considerably higher than 170 to develop 170 degree air because the radiator isn't perfectly efficient in transferring heat. Hayden says that the coolant is about 30 degrees higher than the air temp. That means it will take about 200 degree coolant to result in fan clutch engagement.
http://www.haydenauto.com/Featured Products-Fan Clutches and Fan Blades/Content.aspx (see embedded links)

180 coolant temp won't provide 170 degree air. The clutch won't engage.
220 coolant temp should provide 170+ degree air. The clutch should have engaged.

If the radiator is shot, it can't transfer heat from engine coolant to the air flowing through. This could be the result of corrosion or scale build-up inside the water tubes, or the air fins can be corroded or not in contact with the water tubes. In other words, the problem can be in the "wet" part of the radiator, or in the "dry" part of the radiator. Either way, heat doesn't transfer, the fan clutch doesn't get warm, so it never engages. That's not the fault of the fan clutch...it's the fault of the defective radiator.

For the record, 220 degrees is NOTHING. Most engine "Hot" light sensors won't trigger until 240, 250, or 260 degrees. Modern cars don't turn on the fans until 210 or 220.

Does the vacuum advance work at idle? (does the vacuum advance work, and is it on manifold vacuum?)

Do you ever hear the fan clutch engage? It's unmistakable. The engine warms up (fast idle is best), the fan blows a lot of air. You think the clutch is engaged, but it isn't. Then--SUDDENLY--there's a friggin' tornado under your hood. The fan is ROARING. Dorothy and Toto fly around the engine compartment. If you never hear a SUDDEN and VIGOROUS fan engagement, the clutch is not engaging. I believe most folks have never heard a fan clutch engage, so they have no frame of reference.

 

Hayden says 3 turns or more on a HOT engine, it's toast.

I can't copy the link to the .pdf download, but it's embedded in the other link I posted above, and here:

http://www.haydenauto.com/Featured Products-Fan Clutches and Fan Blades/Content.aspx

 

That's what I expected. Non-Thermal (Centrifugal) fan clutches are crap. GM--Ford--Chrysler--AMC wouldn't have used 'em. OTOH, I don't know everything about every car, and I was prepared to learn something. I suppose some application, somewhere, has a non-Thermal fan as OEM.

I have heard that fan clutches built in the '60s used a lower engagement temperature than those built later. I have not confirmed this, but the guy who told me was entirely convinced.

 

Interesting read, but, several dependent and independent variables aren't taken into consideration such as -

- shroud depth
- fan blade depth
- fan blade count in relation to total rotational disk
- relation of fan blade depth to shroud depth
- pitch angle of blade in relation to diameter .. and both of these in relation to RPM
- RPM distribution relative to optimal flow fan design
- shroud inlet area in relation to exit area

.. and a lot more

I have a few friends still employed here with Grumman in my airplane club .. I will put them to task on this. If nothing else, it will provide them with several hours of argumentative discussion

 

I have the (short body) high performance water pump, and new fan shroud from TaPerformance. ('67 Electra, 430)
Original radiator. And replacing my 4 blade to a 7 clutch-blade fan #3462186 for '74-'79 Mopar with 2.75" pitch.

Summit lists Hayden 2747 HD clutch for both '67 Electra and '74 RoadRunner/Charger.
But some mentions it to be noisy. buickperformanceclub likes the 2797/NAPA 271301 but thinks its
noise before modifying it.

I got curious what the difference was between 2747 and 2947:
2797 = 3.66 height 3.25 bolt circle 2.62 fan mount dia. 2.58 mount dia. 6.45 over all dia 0.63 pilot depth 0.63 pilot dia.
2747 = 3.34 height 3.25 bolt circle 2.62 fan mount dia. 2.59 mount dia. 7.2 over all dia 0.56 pilot depth 0.75 pilot dia.
2747 =Heavy duty. 70-90% of the shaft speed when engaged. 25-35% when disengaged.
2947 = Severe duty. 80-90% of the shaft speed when engaged. 20-30% when disengaged.

Which makes me think that heavy duty would be better since it cools more disengaged and perhaps doesn’t need to engage as often as the severe duty in the city. Cooler and quieter.
My biggest concern is to find one with the right height. So I get the right distance to the radiator.

So I wonder if there are some other recommended clutches?

 

I'm trying out a 2765 this year which is REALLY short. The fan on my 1970 now sits with about .5-.750 inches of the fan outside the shroud VS being nearly flush like it was with the 2747. I had to shorten up the studs in the waterpump to make it mount up but when i pulled the original fan clutch 20 years ago it was the same PITA to remove that this one will be It will require you to start all 4 nuts before tightening them down. Its that close... FWIW I have noticed ZERO change in temps for my efforts.

 

Automotive fans throw a LOT of air "outwards", as opposed to blowing it "back".

The fan should be somewhere between 1/2 in the shroud, 1/2 out of the shroud, and 1/3 in, 2/3 out.

 

IIRC the factory idiot "HOT" light doesn't turn on till 256 degrees.
When I towed with my '75 Electra on a long uphill, you knew when that clutch engaged, the car lost speed and the fan roared!

 

If you decide to use the SD 2797, the cut-in temperature point needs to be modified (there's a write up on the PY pontiac board). It engages at a higher temp than the other clutches. It will be noisy, it will move a lot of air and it will suck up alot of hp.

 

How close should the fan clutch be to the radiator?
I checked my new Hayden 2747HD and it’s like 1.57” from the radiator which seems much.
Should I find a 1” or 1/2" spacer?


"The Flex-a-lite fan spacer kit is best when used with Flex-a-lite belt fan. Belt driven fans perform best when they are 3/4" to 1" from the radiator's surface." Flex-a-lite 14548 - 1" fan spacer kit.
Do Flex-a-lite make good spacers?


Allstar Performance ALL30182 - 1" looks more solid.
But one of the comments was that these put too much strain on the pump bearings.

Derale Flex Fan spacer - 1" 31510