Going to disagree with you to some extent pfarber. If the engine is still pretty new, then at idle (depending on idle speed) it will have more than 10psi even when hot. My old 261 would hold around 30psi at hot idle with appx 20,000 miles on it. Would peg the gauge when cold. At highway speeds would hold about 45psi when hot.
The relief valve in the oil pump does much more work than you might think. With the oil pump and new bearings throughout the engine, it can build lots of pressure on the system in a hurry so the relief valve helps to "dump" the excess oil (and lowers the pressure) back into the pan rather than forcing it through the engine at such an extreme pressure.
I bet when he gets the relief valve working properly his oil pressure problem will be fixed. His engine should be set up for full flow filtration so he also needs to make sure he uses full flow filtration.
If the bearings (especially rod and main bearings) were not installed correctly the engine likely wouldn't turn over. Even if it did start, it wouldn't run long without obvious signs of troubles.
If any of the oil passages were blocked due to dirt or sludge then the engine would also show signs of bearing troubles very early in the run cycle. Rod and main bearings just don't do well without a steady supply of oil.
The oil pump in the engine isn't that different to a hydraulic pump on a machine. Just pumps a different kind of oil for a different purpose.
