At the age of 16 years, I learned the hard way (twice) about fan blades. Coming home from work one night, I wound up Dad's '51 Henry J six in the middle of Coyote pass leaving East L.A. One of the four blades of the fan broke off and came through the hood......started shaking like hell. Back to Ford Blvd. on the way to work for a hood and another fan. Cost me a weeks pay and he was more than upset.
THEN, maybe eight months later, in the same place, I was copilot in Dad's other chopped and channeled '51 Henry J when HE wound that little hot rod flathead four up and did the same thing except this time it sliced a hole in the top tank of the radiator. He detonated on me even though I tactfully pointed out that HE was driving, not me. I still had to remove the HOT blade right there in the dark while he stomped around looking at his custom Henry J hood with the '50 Merc nose leaded in. Lessons.........
The '54 vintage Chevy six has a stock water pump/fan ratio of 1.41. The fan runs faster than the crankshaft. 4000 rpm crank = 5640 fan rpm.
On my 235, I needed a later Chevy Harmonic balancer (6.75" instead of the 6.0" original) to bolt the serpentine drive pulley onto. Now the ratio changes to 1.59. 4000 crank rpm = 6352 fan rpm (Scary!!)
The answer is a larger water pump pulley, but which one? Evidently the dimensions of the multitude of water pump pulleys is classified space shuttle technology. No one wants to share this information, nor is it listed anywhere that I could find.
I finally got a response from a very courteous gentleman at CVF Racing who took the time to sell me a pulley that is close enough to modify and mount on the original '54 Chevy water pump pulley (part # BBFL1WP).
Three modifications are required, bore the center hole to .980, redrill the bolt pattern to 4 on 2.25" bolt circle, and add a 1/8" spacer between the water pump pulley and the new aluminum pulley. This pulley moves the fan forward 3/8" which I need to clear the serpentine idler.
This new pulley is 5.9" in diameter and will result in a pulley ratio of 1.14.
4000 rpm crank = 4560 fan rpm. Much improvement!
As soon as the pulley is back from Dick's machine shop I will summarize the results.