Quote:
Originally Posted by Formulajones
I don't know if I buy into all that. These clutch fans are what GM used on nearly all the high performance solid lifter engines and we zing those things up repeatedly. I don't think GM would have engineered them this way if that clutch fan was going to be a problem above 4800 rpm.
My little DZ loves 7,000 rpm. 51 year old stock clutch fan in place, works just fine.
I have the heavy duty unit on my 454 chevelle and can't tell you how many times I've buzzed that thing to 6500 over the last 35 years, lol.
Dad can't stay off the rev limiter set at 6300 in the GTO, with a heavy duty clutch fan on it.
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The engine is turning 6300, 6500 rpm, but the clutch slips so the fan isn't spinning that fast.
Heavy-duty and Severe-duty clutches slip less, though. (Unless they're used with fans having big pitch/high drag.)
Quote:
Originally Posted by P@blo
Its interesting how the Hayden website says to us"e both the heavy duty and the severe duty clutch the fans over 2.25" pitch.
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THIS is what I found on the Hayden web site.
https://www.haydenauto.com/en/techni...q-fan-clutches
Quote:
What is the difference between a standard, heavy and severe duty fan clutch?
Answer: Each fan clutch type is designed to simulate the performance of the original equipment clutch that it replaces. All fan clutches are for specific applications and should be applied only on the vehicle for which they are cataloged. Use of the incorrect fan clutch may result in poor cooling, excessive noise, reduced fuel economy or fan clutch failure.
• Standard Duty Thermal: Turns the fan 50-60% of shaft speed when engaged. Used with fans with lighter pitch (1-1/2" of pitch). Flat plate impeller design with 30 sq. in. of working surface.
• Heavy-Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged for increased cooling. Used with deeper pitch fans (2 1/2" of pitch). Land and groove design with 47 sq. in. of working area allows higher operating RPM's.
• Severe Duty Thermal: Turns the fan 80-90% of the shaft speed when engaged. Used with deeper pitch fans. (2- 1/2" of pitch). Land and groove design with 65 sq. in. of working area. Larger working surface provides cooler running and longer life expectancy.
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In other words, don't use the HD--SD clutches with typical automotive fans. The HD--SD clutches will never disengage unless they're driving a high-pitched fan that creates a bunch of drag.
Coupled to a fan with less pitch, the fan over-speeds; and it's noisy and wastes power. Maybe even dangerous.
But it will suck a lot of air, so guys use 'em and think they're "great for added cooling". Duh. The thing will never properly disengage. Might as well scrap the clutch and just use a solid spacer if you think you need a "Heavy duty" clutch on a wimpy fan. Don't forget to armor-plate the under side of the hood.
What I did not see was any mention of Hayden selling fans other than electric fans any more. There used to be three part numbers for clutch-style fans, two in the normal direction, and one for reverse rotation. None of the non-electric fans are in the catalog any more.