8.1l rebuilt engine low oil pressure
 

ok 03 8.1l bored.060 over. crank measured stock clearances. melling oil pump 10w30 valvaline oil

since first start up i have had 45-50 psi of oil pressure at start up and once warm i get about 20 psi at idle and 40 at 2000 rpms

seems a bit low to me. havent put a manual gauge on yet but since the machine shop took all the plugs out im wondering if there was a restrictor some where that should have got put in and didnt

You should be fine, I haven't checked on the 8.1 but the 454 vortec's spec for hot idle is 20 psi.

Technically it's fine oil pressure, as long as they're making 10psi for every 1000rpm you're good, but in mine I do like to see 30psi at idle when the oil is at it's hottest. Which Melling pump do you have, the HP or HV?

i have the hv melling pump.. the thing that really bothers the hell outta me is in wot when the oil is at its hottest the pressure drops.. from 2500-4500rpm it goes from around 40-30

Part Number: M-77HV

Yep, that's the high volume, same as the one in my build... and No the OP falling off like that isn't normal. Either one of two things is happening, you have too much clearance somewhere, OR, is the oil is sloshing away from the pickup tube, and the pump has enough balls to start sucking air. That isn't unheard of with the HV pumps. Another possibility is the pickup tube has fallen off the pump.

My suggestion is to add an extra quart of oil and see what it does.

Speaking of the oil galleys... Not sure what they're doing with them, but indeed, many kits I see have two plugs with holes in them to lube the timing set, and you really should only need one. If the main galley plug has a hole in it I doubt you'd be making that much OP. If the extra qt of oil doesn't have an effect, I'd start asking questions to whomever assembled your engine.

its due for a oil change anyway so ill change the oil tomorrow and see if that does it.. also gonna go to a little heavier oil... machine shop did the machine work and i did the full assembly

added a quart of oil.. no change.. wot drops pressure still.. gonna swap out oil pressure sending unit.. if that doesnt give me a answer then its time for a manual gauge and then dropping the pan

HV oil pump was the issue... changed to oe pump and sits at 40psi at idle and goes up with speed of the engine