Low oil pressure?

Talked to Larry Shepard yesterday and asking the question of the effective of leaving the plug out. The first thing he said was
"You want that plug in there or you won't have oil pressure."
I ask what happens when the plug is left out?
His answer was that the oil coming up from the pump going through the two passages then hits head on at the end of the passage where it turns to go up into the motor.
I said so it's the two passages coming together causing turbulence that is causing this problem he says yes. He said but turbulence is not the word that I'm looking for and I can't think of it.