between loose bearing clearances and probably wide rod side clearance the bottom ends a "bleeder". this seems to be very similar to a build i had a couple of years ago. mine was 18psi hot idling in gear with a heavy base stock 30wt oil and half groove mains. i tightened the bearing clearances up (.0005"-.0007" tighter), got rid of half the rod side clearance (i will never believe side clearance doesn't effect pressure. it's a hole, it's a leak!) and more than doubled low rpm pressure (with added full groove mains) and the engine runs smoother