oil pressure question

had the f-head rebuilt and then it spun a couple rod bearings was running at 5 psi. turns out the engine guy installed the wrong size bearings so we replaced those. he also used a melling oil pump and it is installed now and i got the jeep running tonight. now it idles at 20 psi but when i hit the gas it goes up to 40-45 psi but no higher. actually when it hits 40 it seems to drop and fluctuate in pressure. whats up with this? i dont want to run it now because im afraid of having the same thing happen again. should i install the original oil pump to see what that does or bad idea?

 

I'd run it as is, 40-45 is good PSI.
you know the problem was corrected
I can't see going back to an old pump
I would drive it and watch it

 

My new oil pump (supplied by machine shop) locked up (broke pump gear), so i put the original one back in my L-head and pumps at 40 or so psi.

 

Tidbits from FSM: "Safe minimum pressure is 6 lbs at idle".. and 20 lbs at 2000 rpm". Drive it. I might stick close for a 100 miles or so to just monitor what happens. If it starts to drop significantly, I would be concerned.

 

Not sure about the details of the F-head, but typical design has a pressure relief valve that prevents the pressure from going over some set limit. 40-50 psi is a typical setting - my pickup has 45 psi hot and 25 at idle and I consider that very good. A rule-of-thumb from Smokey Yunick (famous engine and racecar builder) is 10 psi per 1000 RPM. So, you are well protected by 45 psi peak.

The fluctuations you see could be the pressure relief valve opening and closing. As mentioned, I would worry if I saw a significant drop, but otherwise it's fine.

 

that is probably were your relief valve is set.if you want more oil pressure at higher rpm you can shim or change spring