Sirrotica, I appreciate the input.
I suspect the back of the block gets the least cooling and would be more prone to localized boiling. What might make it worse is my ac system's heater control valve, which stops all flow through the core, and prohibits the 3rd parallel flow path in the cooling system (heater+recirc+radiator) Without the heater flowpath the coolant won't have as much differential pressure to promote flow at the backside of the passenger side of the block, which equals bad. But then again, if there is no bypass flow through a heater hose, then it would provide more flow capability through the radiator path. Which benefits more? I don't know.
More flow is always better, even in those localized hotter spots. As nucleate boiling occurs along the channel walls, more flow strips away the emerging steam bubbles, which is great heat transfer. Lower flow allows the steam bubbles to coalesce, which creates a steam layer that drastically inhibits heat transfer. Yeah, that back half would have the lowest flow. Maybe that is why Pontiac (maybe all GM?) got rid of heater control valves early in the 70's?
Steve Barcak years ago talked about the hole in the deck surface that needs to be drilled, so you reminded me that was a thing.
I'd be curious what kind of dead head pressure a Pontiac water pump could make, and how much that pressure head takes things away from saturation. There are two means by which to keep from boiling: increase pressure, or lower temperature. If you increase back pressure, you move the system farther from saturation. But you also reduce flow, which reduces heat transfer, and promotes more saturation conditions. Which one wins the day?
With regard to the Champion, I remember Chris Casperson years ago proving to me that a properly designed 2 core is better than a 4 core - number of rows isn't the only metric. Total surface area of the rows is what matters.
I'm gonna roll with my Champion for now, unless I can find a way to squeeze a 28x17 radiator in. Battery tray placement is my current limiter for that. I STILL have yet to do a good chemical flush of the system to possibly address any surface area sludge coating. And I still need to replace lower hose and spring.
Yeah, the idle heating bothers me. It is very manageable for now, but it seems like it will be very air speed and ambient temperature dependent. And then there is the AC charge coming soon...
Yes, the EFI fattens up the fuel mix when less than certain breakpoints. 170 is the default FiTech breakpoint for normal op temperature, but I recently found out that I can change that. I set it to 150 for my current configuration.