lifter galley crossover tube
Oil control is hardly simple physics. Making anything perfect is also impossible....
Back on the topic....it's tempting to go to an external pump and pipe the oil into the front oil feed port on the R3 block. Though I am not seeing the benefit over the 'rear feed' of a stock engine. If #4 is starved when you rear feed, #2 would be starved when you front feed. I'm think a true 'loop feed' (front and rear) would be worth looking into.
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Oil control is pretty simple when looking at how complex fluid dynamics can get. We're not dealing with supersonic flow, compressibility or latent heat or anything. It's literally just momentum, pressure, head and boundary layers. Most of which can be assumed away for a multitude of reasons. Aeration and windage are their own thing, but are well understood enough to be dealt with separately.
The idea behind the cross over is to help with mains starvation caused by the compromised OEM oil system which was intended to be easy to mass produce. Remaining constrained by that OEM routing seems silly when routing tubes isn't hard, it's just work.
Racing blocks used in sustained high rpm applications went to a priory main feed for this and other reasons and generally solved the issue, and lots of used parts show evidence of dedicated mains feeds in the cap. Seems like a bulletproof way to ensure both mains and rods remain oiled and actual physical findings support that approach. Ample grooving of the bearings can help, but only within some reasonable limit before more support is taken away than the system can handle when constrained by the main journal width of an OEM crank.
If one wanted to try and work within the OEM architecture, it should be possible to create a dedicated main feed for each journal in the main oil galley by using several spaced plugs in the lifter block off tubes. Then feed those spaced chambers with tubes tapped into the filtered oil supply at the rear of the block. Super undersized bearings with a maximum groove depth would also be a benefit, not to mention slowing the bearing velocity at the expense of absolute strength. A stepped tube could even be used to help balance flow supply to each main saddle. Similar to the way air ducts narrow down after each register.
It may even be possible to cut a deep groove into the bearing saddles of the block and route oil from the main feed to the bottom bearing shell (with a matching groove in the main cap which communicates with the groove in the bearing saddle in the block). This would be similar to what YR described, but without the external tubing. Fixing the supply to each main would still rely on addressing the supply imbalance at the main galleries though.
None of these are complex, but they are definitely outside the realm of mass production.
