hard or soft copper line for a valley oil gallery bypass line?

92b said
What you said was "Having opposing feeds in the same gallery can stop flow at some point in the pipe." When I read that statement it struck me. It's not how I understood how hydraulics work. Maybe my understanding is wrong and I can learn something from this. That's why I asked you why you believe this to be true and if you could point me to some evidence to support your claim. Some of the lessons I've learned best are the ones I had wrong.

You have me mixed up with someone else.

Ok, it was explained to me in 1986 how that works. The guy is dead now and has been dead since 1995 so I can’t just ring him up and explain it to me in detail again.

The upshot was that two columns of fluid (most likely at different pressures) in the same pipe or tube is the side with higher pressure is fighting to overcome the lower pressure side. And it goes back and forth as the pressure changes.

Again, what do you gain adding another feed? You don’t. It’s not a feed or speed issue. That’s why big blocks smoke 5 and 6 get ate. You are feeding two shafts and 16 rockers and all those leaks off one main bearing.

The fix is to not feed the rockers off of one main or even two, especially when the cam has grooved mains.

If the OP is concerned with bearing life there are better things to do like stopping as many useless leaks as he can, forcing the oil to the mains and and working on the suction side of the pump.

The crossover does none of that.