oil pressure and crankcase pressure

If your oil pressure is too high, look into your oil pump. The oil pump has the pressure releif valve and spring that sets the pressure for the engine. The stiffer the spring for the relief valve, the higher the oil pressure that the engine will run. The relief valve bleeds off any pressure excess of what the spring is designed for. I have run the MP high volume pump with the high pressure spring and typically run 75 - 100 lbs with no problems.

I had a bad experience with a TRW oil pump 30 years ago. The pressure relief valve stuck between open and close and had no oil pressure. TRW rebuilt the pump for free, but did not compensate me for my engine damage. I sold the pump to someone for $25 and warned them what happened and to this day do not run TRW parts. Their "lab" analysis for my failure from TRW was and I quote:

"Small tiny minute particles small enough to fit through a stock oil pump pick up screen" had gotten wedged between the valve and valve bore and caused the valve to stick. I say if it can't handle what the pickup screen filters out, it is junk. I have run MP and Mellings pumps ever since with no problems. This was on a very clean 50k mile 70 340 that was disassembled and readdembled with a new cam and TRW pump. I changed the oil three times within 500 miles because the car sat in a body shop for a while and I did not want body dust in the oil.

So basically, the spring sets the pressure, and the valve blows off the excess above what the spring is calibrated for.