They came standard on 69 Z28's, so no doubt they were rated for 7000 to 8000 engine rpm's.

 

I don't think you can over spin it. They were used on the 302 engine and they sometimes revved to 8k and up.

Beat by one minute!

 

This fan was coupled to a fan clutch, so I don't think those fans got up that high as the internal viscosity clutch would free wheel or release. This was a great deal in slow traffic.

 

This. That's what came std on my 70 Z28.

 

Thanks everyone for the prompt reply. Just looking to change my pulley ratio to draw more air at idle without exceeding the fan's max speed.

 

Over driving the WP and fan is not a very good idea.

Do you have the proper fan shroud installed?

 

Shroud is correct.

I plan on using a photo tach this weekend to look at fan speed and see if the clutch is performing correctly.

 

With the clutch, chances are overdriving it would only result in more slippage in the clutch, not more air movement. This would then result in more heat in the clutch (see those fins on it? The are there for a reason). You may have a dying clutch which is slipping too much. The only other way would be to somehow drain the fluid and fill it with something thicker. Or put on an electric fan or flex fan.


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That's a good idea. It would be great if someone with a known good fan would publish a baseline of testing results. Something like "at engine rpm x, fan rpm is y" at several different rpm points. Folks may even be able to use a simple flash strobe app on their phones to verify? This may be overly simple as it doesn't take into the thermostatic properties of the fan.


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Understanding what you are saying but both testing point need to have the same ambient temp?

Humans are not known to service those viscous fan clutches. They are sealed and besides Hayen may use different fluid than GM.

I too and thinking of a dying clutch. But what ever clutch you buy, I am told not to buy the HD clutch. Read it on this site.