Stovebolt.com Forums The Shop Area The Engine Shop 235 block water inlets

I'm trying to compare the water flow capacity of the early vs. late engines and pumps.
ve made a rough guess (via Photoshop) of the late water inlet at about 5-7/16" diameter, and the 2 smaller early holes at about 1-9/16" each.
Is this pretty close?
Forgive me, I don't have the parts where I can measure them.

That is a quite the challenge right there.
I am sure that you have considered:
Water pump pulley diameter difference.
Crankshaft pulley diameter difference (?).
Impeller design/size difference.
Your estimates of the block hole sizes seem very close to correct. Close enough, given that you are probably looking for a percent difference in total square inches of hole area between the two designs.

Thanks.
The late pump flow in GPM (with the same drive pulley ratio) is about 72% higher accoding to GM data, but I think the driving factor of that huge hole is the pump impeller diameter, it's many times larger than +72%: 23" vs. 4" areas.
I would guess that locating the smaller holes way up is Chevy's way of getting the coldest water to the hottest area of the #1, and the bigger late hole is the price you pay for simplifying parts - too much water reaches the entire face of the #1 jacket. There is no obvious way to mask part of that opening, unless you want to insert and attach a plate inside the block to direct flow upward, but how and made of what?
This "#1 too cold" supposedly plagued many L6 truck engines in long service: the hot #6 made it knock, but the cold #1 wore out its rings due to distortion and started burning oil first.