Mechanical Cooling Fan broke during 6000 rpm burnout.

slant6/4speed said

Remember everyone-Fan RPM is not the same as engine RPM. You have pulley ratios to figure out to find the fan RPM.

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This is what I was thinking. Might try looking for a different set of pulleys. I think the AC cars used water pumps with more blades on the impellers but also used a larger pump pulley to slow the pump down a bit.