A friend rebuilt a 250 Chevy and is wondering about what he thinks is low oil pressure at idle.The engine has new pistons,crank machined,all bearings replaced and so on.Him and an experienced mechanic friend assembled the engine.
With the engine fully warmed up with 10/30 oil the pressure at a 500 rpm idle is 20 psi.Running down the road is 45 psi.
I think the pressure is just fine.The slightly low pressure at idle is likely a bit excessive clearances on the bearings and or oil pump.

I think 20 psi at 500 rpm is fine if that is warm. It's not doing any work there. As long as it comes up quickly. An old rule of thumb is 10 psi per 1,000 rpm. That's in our older engines for street use. 45 psi down the road is fine.

were the cam bearings replaced as well?

He says yes and the crank journals were miked after the machine work.

The 10 PSI is said quite often ,I read it to. Think about it,if you were buzzin the engine along at 3000 rpm on a fresh rebuild and only 30 psi that makes ya nervous.I believe it's a racing thing,other words,60 psi at 6000 rpm.

20 psi sounds ok for 500 rpm. The rpm sounds low to me. I think timing for most of these and idle for factory setups is 625-650. I bet the oil pressure would come up more then.

I would be a little concerned on clearences as I am running a Chevy 194 motor with stock parts inside and unknown when it was rebuild to (.040 over) that has 30# oil pressure at 900 RPM and 60# at 5500 on top end.

Was a new oil pump installed as part of the rebuild?

TOTALLY NORMAL

sounds like it may be normal, bump the idle up like others said, 500 is too low. I like to keep the idle a tad high on old engines to ensure oil reaches every last part of the intended path. I'd go over 750rpms. Don't know what trans you are running, you need to stay below a certain point with auto trannies so they don't start stalling the engine when you are stopped and in drive. 1300rpm idle would not work Had a guy bring an older malibu to the shop with a new high perf 350 in it, he complained about stalling at every damn red light, and he kept adjusting the idle up. Must have idled 1200-1300. I dropped it to 800 and his stalling problem disappeared. Go figure

It's a manual tranny. The pressure goes up to about 40 at 1200 rpm.Told him to raise the idle.