Think it through. If you have 80 PSI at one end of a pipe (oil gallery in this example) and lets say 70 PSI at the other end of the pipe then you can understand that somewhere in that length of pipe there will be pressure but no flow. And the point of no flow can move back and forth in the pipe as the different leaks off of the pipe come and go.
Of course, if you have full groove mains then some oil is always going out to the rods but even then the leak at the bearing will be more when the the oil holes are lined up in the crank and block.
So just sticking an extra feed line in the system isn't the answer.
Thinking about it...if I were to do something like that when I tubed the block I would close of the ends of the pipe where they meet in the middle. Then you'd be feeding 2 mains from one feed and 3 from the other.
So no contradiction at all. You can have pressure and no flow. It happens in fuel systems all the time. Well, not as much any more because fuel systems have gotten better. But I still see it every now and then.
These oiling systems are simple hydraulics. System pressures vary a bit, say from what the gauge says and what the rockers and shafts see.
When I bought my first W2 engine the oiling system (for a wet sump) was sorted out. After a year I took it down for freshening and upgrades. And everyone to a man except me wanted to change it. That required removing some plugs blocking the feed from the lifter gallery. Once those came out, I couldn't keep a rod bearing in it to save my ***. Then I hurt the crank and when I did that it got worse because no one would cross drill it. Eventually I did cross drill it myself and I put the restrictors back in where they went. I NEVER hurt another bearing, even when losing focus ad shifting at 9k rather than 8500.
Like porting heads, you have to know where the oil is going and WHY it's going there. If you don't, it's a crap shoot on bearing survival.
To sum it up, the cross over has its place but its not some secret squirrel **** voodoo magic. It's pure hydraulics. And to that end, IMO guys need to spend way more time on the pickup side of the pump and not the other stuff. The biggest restriction in the oiling system is the suction side of the pump, not on the pressure side. Get the inlet to the pump as big as you can, use a rear sump pan, full groove bearings, stop the leaks at the lifters and you can shift at 9k plus and not hurt a bearing. If you don't' do the former but add the crossover you didn't fix anything.
