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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2019 Pontiac Heaven class winner
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