Running 570cid-600hp+ w/ high volume pump. Oil pressure during start-up,cruise 32-3600rpm, and once hot run great at 65-70psi. When I take engines up to 4000rpm - 5400rpm the oil pressure in the starboard motor drops to 25-40psi respectively to the rpm. Higher the rpm lower the pressure. Take the rpm back to cruise at 3200-3600 and pressure comes back to 65psi. When hot both motors idle at 50psi. Port engine rock solid at 70psi cold/running - 50psi idle. Starboard was the same until I pulled out of storage after this last winter. What is going on?????????

Sounds like you're sucking the pan dry or have a bad sending unit.

Check true pressure with a mechanical gauge,cut open the filter and check for debris. A nice filter cutter is under 50$,I just bought one myself I liked crocketts so much,Smitty

what do the oil temps do?

when you figure it out let me know, i have been having the same problem with one og my motors all summer

changed relief valves in blocks, replumbed oil lines. When i put a new filter on it is good for a day or two and then the problem comes back

Maybe a cracked oil pick-up?

Could also be windage. If the oil level is too high, the crankshaft counterweights are beating air bubbles into the oil, and sucked up by oil pump. I'd try dropping the oil level 1-2 quarts and do a short repeat just to see if it is the problem. If the problem actually then becomes worse, then you may need an improved engine oil cooler.

Windage, you need more low pressure area in the pan to disspate the high pressure created by the rotating parts. The fix is a larger pan.

Would it make any difference if you increased the vent size at the valve covers?

Breathers are upstairs, oil is downstairs. Your problem is in the basement. You can test to see if windage is the problem by lowering your oil level 1-2 quarts. Watch gauge closely and only do this for a short run.