i have a mark iv 515" big block chevy
-4' gm crank
-h beam rods
-wiseco aluminum mini dome pistons
-milodon oil pan 31557
-melling 10774 oil pump with milodon pickup roughly a little over 1/4" clearance from pan bottom
-block was line honed this winter and main bearings have .0025 clearance
-johnson +.300 tall hydraulic roller lifters
-comp 11-456-8 camshaft 242-248 @.050 and .566 lift intake and exhaust
-davis unified ignition hei distributor
-10w30 vr1 is oil used
-10 quarts of oil

long story short my engine has 55-60 lbs of oil pressure as long as i stay under 4000 rpm and anything over it drops as low as 25 lbs. engine has been run over 5 minutes in the water and maintains 55-60 lbs but drops at any higher rpms than 3800.

i can ride around all day long at any rpm under 4000ish and oil pressure is great!

IM AT A LOSS AND DO NOT KNOW WHERE TO GO FROM HERE!!! ANY SUGGESTIONS ARE GREATLY APPRECIATED

I wonder if your airating the oil or its just not draining back to pan fast enough, pooling in heads / valley. Not sure how to prove that out.

-Nick

did have my buddy pull breather out of valve cover and there is oil up top but nothing excessive. its draining back as it should and we were running at 3900-4000 when he checked

Does it consistently stay low or bounce around a bit? Maybe a thicker oil ?

it stays 35-50 at idle when warm after making a 5-10 minute run at 3800rpm. at 3800 rpm it stays 55-60 when running. anything over 4000-4100 it will drop quickly and sit at 20-25

i pulled the motor over the winter and went through it because of the same issue and its still happening.

Maybe cavitation in the oil pump, have you tried a thicker oil ? 20w50?

no cavitation in oil I've already eliminated that issue by running it until it quit by reducing oil level

Not sure what you mean by that ? Did reducing the oil level make the problem quit ?

Also 10774 is not an oil pump number. Which pan do you have ? I am thinking maybe you have the pickup a little too close to the bottom ? I like to see more like 3/8 to 1/2

oil pump is a melling 10774...

broke the engine in on a stand and it was definitely cavitating. so i removed a quart at a time until it quit.

my pan is a milodon 31557.

Okay, it’s listed as a ten quart pan. In case someone else uses that pan at sometime, wanna’ share how many quarts keeps you out of this oil psi issue ? :wink