Jamesc says it well, here is my take on it. Pump rotors big enough to supply max flow needed. By pass set to give proper max pressure. I run 65 psi HOT with 20w50. With steel rods. Passages big enough to flow more than enough oil to the bearings at all times. Bearing clearances sized to provide the proper hydrodynamic oil wedge, determined by the hp level and weight of the oil. 3/4 grove mains work for me. 7800 rpm, 4.15 stroke, 2.375 rod bearings, 900 hp.