No you would not be wrong on that point. Higher RPM would definitely see a reduced pressure if the suction side is restricted. Oil pressure is totally dependent on clearances in the complete system. Since rods have side clearances they are usually not a big factor considering the mains only allow metered flow. Some engines such as Ford FE's allow unmetered flow to the rockers which has always been a pressure issue in those engines. There is simply far too much oil fed there and by restricting it you can increase pressure to the rest of the engine dramatically. On to the rest of the equation. Since rod bearing clearance is a big issue and will make noise lets go on to the rest. If the mains are loose, you will see pressure rise with RPM and fall at steady throttle, if you ease off the throttle and see pressure go up a bit then you have too much clearance there. Cam bearings will lower pressure and there is nothing that will change that short of thicker oil either when cold or hot, hot will be lower. You have 5 feed holes directly to the pump that are letting more oil bleed off around those bearings ALL THE TIME hot or cold. Cam bearing clearance is about as critical as you can get in an engine ! Since the cam spins half the RPM clearances are held much tighter than rods and mains. There is less heat here, and with all those springs pushing in the same direction, depending on engine oil system design, some engines feed oil from the top and others feed oil from the bottom. Those that feed oil from the bottom are less affected than the other way, as oil is fed to the cam journal from the bottom the downward pressure keeps the cam closer to the feed hole restricting bleed off, the other way around gives the opposite affect. The other thing that affects oil pressure is the pump itself, clearances in there, end clearance in the pump/gear assembly, clearance between the gear teeth and then there is the pressure relief valve and spring ! Obviously if the engine is old the pump is worn since it gets all the crap from the rest of the engine first hand from the bottom of the pan before it gets filtered out !!!! Oil pumps are for sure easier to deal with then cam bearings. That should be the first thing to address on any engine that has problems. Just ask a shop tech that has worked on newer LS engines or any other engine that uses an aluminum body pump, AMC, Buick, Toyota, Ford in some cases, there are others but what's it matter. I don't recall seeing a MOPAR with an aluminum pump body. As we all know Aluminum expands more and faster than iron so it starts with too much clearance and gets worse. The result is obvious. GET it out of there and put in a good one. And before you put it in take it apart and check those clearances. End clearance in a pump body is easy to fix and it is the worst worry as oil that flows under those gears is not picked up by the next tooth as well as what gets from one tooth to the next. From that point you can roll in new bearings on the crank but if that isn't enough well you know what comes next. Pull that engine and disassemble it for new cam bearings. Those are your options. Thick oil wastes power!
