[Formulajones]

Originally Posted by STEELCITYFIREBIRD

IIRC... that is SOP on A/C equipped Pontiac's, over driven water pump....under driven pump on non A/C cars.

Correct. Matter of fact it's a pretty common trick as far back as I can remember to put an AC water pump pulley on a non AC car for someone looking for a little more pump speed.

[Formulajones]

Originally Posted by P@blo

Just to add to the confusion Hayden themselves indicated to use the heavy duty clutch for my application.

I really don't see an issue with that.

I run the heavy duty clutch on my chevelle that I spin to 6500, it's been that way for 35 years, and it's an AC car with the very small water pump pulley, which increases pump speed. It's never been an issue, makes 600hp and I can't get that engine over 175 degrees in the AZ summer heat buzzing 3500 rpm down the freeway.

As another example, dad's 571 makes 724hp. Identical cooling system setup with a HD clutch on the stock fan, stock shroud, and I do believe we stuck an AC water pump pulley on that car many years ago (it's a non AC car) for more pump speed. You'd think from everything you hear on the internet there is no way to cool a big engine making that kind of power on the street.
Again this thing runs very cool, never gets over 180 on the highway buzzing 3000-3200 rpm, and around town at slow speeds the engine actually gets very cool at around 155-160. It'll idle all day long in traffic and never budge. After a pass at the track, driving back the return road it's actually cooled down to 155 degrees by the time he gets back to the pits.

[68 Firebird]

Well seeing the hole in OP’s hood had me cringing.
And the fact my car was over diving the factory flex
Fan had me a little concerned(AC pulley set with no AC).
So I ordered a Napa Standard duty Thermal fan clutch and used a 7 blade AC fan
I was using as garage art(10008888). Well after a half hour
Drive the results were ok. Temp stayed 165-170 and zero
Fan noise. All done to avoid putting an extra vent hole in my
Hood. Just wanted to see the comparison since switching to
A cold case radiator last January.

[Jack Gifford]

Originally Posted by Jack Gifford

... I've NEVER seen a water pump pulley smaller than its crank pulley...

Well... that was a truthful statement... true but ignorant!!!
[what would you expect from a guy who drives a 1917 Buick every day?]

[Schurkey]

Originally Posted by P@blo

Just to add to the confusion Hayden themselves indicated to use the heavy duty clutch for my application.

Apparently, "your application" includes a deeply-pitched fan suitable for use with the Heavy-Duty clutch.

Originally Posted by Formulajones

I run the heavy duty clutch on my chevelle that I spin to 6500, it's been that way for 35 years, and it's an AC car with the very small water pump pulley, which increases pump speed. It's never been an issue, makes 600hp and I can't get that engine over 175 degrees in the AZ summer heat buzzing 3500 rpm down the freeway.

As another example, dad's 571 makes 724hp. Identical cooling system setup with a HD clutch on the stock fan, stock shroud, and I do believe we stuck an AC water pump pulley on that car many years ago (it's a non AC car) for more pump speed. You'd think from everything you hear on the internet there is no way to cool a big engine making that kind of power on the street.
Again this thing runs very cool, never gets over 180 on the highway buzzing 3000-3200 rpm, and around town at slow speeds the engine actually gets very cool at around 155-160. It'll idle all day long in traffic and never budge. After a pass at the track, driving back the return road it's actually cooled down to 155 degrees by the time he gets back to the pits.

"Cools great" because the clutch likely never disengages properly, and when it is engaged, it spins the fan faster than if you were using a Standard-Duty clutch.

What is the pitch of the two fans? Any chance they happen to be deep-pitch units like Hayden specifies?

It's working for you. That doesn't mean it's an optimum system.

[Formulajones]

I'm positive they disengage because you can hear the typical fan noise disappear as you accelerate down the road at a normal pace, much like my other clutch fan cars do.

I don't know the pitch of the fans. The Chevelle has it's original 7 blade clutch fan with an added HD clutch, and the one on the GTO was an OEM GM clutch fan that we had in the stash of spare fans, with a new HD clutch on it.

I don't know what you consider optimum but when we have these big engines making pretty respectable HP, and can make them run cool in the Arizona desert heat, it's a win all around in my book

I have no interest in changing it. We made that mistake on dad's GTO thinking there was something better. All that caused was a hot car, found out very quickly the stock setup with an HD clutch and a good radiator not only keeps it more than cool enough, it works better than anything else I tried.

[HWYSTR455]

Believe when Schurkey mentioned 'optimal' it was in reference to the fan disengaging at an appropriate rate. The HD fans engage more at lower RPMs and never fully disengage like a 'standard duty' clutch will. But obviously, a slight loss of power/HP is not a concern in your app.

I believe the bearing is larger in the HD clutches too, which help them last longer, but it's been a while since I used one.

HD clutches do have a tendency to shorten belt life, something to keep an eye on.

Many do the AC pulley 'upgrade' and overlook the fact that, depending on the year/series of pulley setup, also require the crank pulley as well to maintain proper groove alignment. On the pre-70 setups, the diff between the AC and non-AC crank pulley is about a half a groove distance different. The dreaded belt-squeal is a tell-tale sign.

New OE-type replacement fans are available, and are a safe way to go when going to a clutch fan. Originals can and do fail. If you're running over say 5-5500 RPM regularly, it's not a bad idea to use a new one over an original that's been in piles and kicked around over the years.

.

[P@blo]

1975 stock 455 with AC and Hayden recommended the 2747 heavy duty clutch.

[1968GTO421]

Originally Posted by HWYSTR455

New OE-type replacement fans are available, and are a safe way to go when going to a clutch fan. Originals can and do fail. If you're running over say 5-5500 RPM regularly, it's not a bad idea to use a new one over an original that's been in piles and kicked around over the years.

.

Sounds good to me. Is anyone besides Ames selling quality new OE-type replacement fans ?

Thanks