I think you misunderstood me. The only components re-used in the "new" configuration was the block and the distributor and I'm not totally sure about the distributor. Everything else was changed including the oil pump. Therefore, the block is quite possibly the problem. Just one of the reasons the questions of block porosity arose. In addition, two different oil pressure sending units were used plus a manual. The manual one confirmed the accuracy of the electric ones. I understand pressure and flow...yet another reason to consider block porosity. A porous section of cast iron will resist the flow of cold oil far more than hot oil. Cold startup I have 55psi at about 60° ambient temp.
I tried two different oil pumps, one a high volume unit and the other stock. The high volume pump achieved nothing. Apart from break-in oil, the only oil this engine has seen is Mobil 1 10-30. I never considered a higher viscosity as I knew from the outset the engine was tight. As regards potential engine damage from higher viscosity oils, that's what I was taught (while apprenticing so many years ago), while also knowing added film strength can be (and usually is) beneficial in extreme environments. I had a brand new Bayliner boat with a Chev 307 and Volvo stern drive. This example doesn't exactly bolster my argument, but that 307 ate two sets of lifters (warranty, thankfully) using the recommended 10-30 weight oil. I switched to Castrol GTX 20-50 and the issue went away although the oil pressure stayed roughly the same. The real issue was never found but the 20-50 seemed to cure it. My Ford 351M would not spin at all with 20-50 in sub-zero weather and risked top end starvation, but would spin fine with 10-30 at -30°F. I take your point, though, on oil viscosity. I just never considered it because the engine was fresh. Thing is...I don't have a pressure problem at startup (55psi)...only when hot, at idle and in gear. Idle RPMs about 750-800 out of gear, less in gear. I could bump that up but this engine is just on the point of needing a high stall converter. A faster idle just makes for a more severe shift into gear.
Mains and rods in the order of .0015 if memory serves. Couldn't measure the cam brgs. Island D Machine reported all was good. As I said to other responders, I'm OK with it personally, having had 20 years and 20k miles with no issues. I disagree with your idea that a lot of oil would have to pass thorough the porosity to affect pressure. It really wouldn't take much although that would depend on the characteristics of the flaw. When the oil is hot and "thin" it will flow like the dickens up to a point, then friction sets in, particularly in something as coarse as a cast iron flaw. The more you try to push through the flaw the harder it is to do, so upstream pressure and flow increases and the problem goes away. Thanks for your interest.
I believe that was a Ford issue with 351-400M or maybe Cleveland. Don't think it was that common. TKS Wanna be my mechanic?
My evening task...I have another engine block and a shop manual. Going to see if I can visually find any potential spots. Thanks. 15-20psi at idle in gear has been my experience too in other Mopars I've owned. That's why I mentioned my other "proven block" that I've owned twice. Thannks.
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