Hi knowledgeable crew!

friend of mine has 200 hours on a full rebuilt 500 efi, never went past 4k rpm except last week end
after keeping it around 4300-4500 for 2-3 minutes, oil pressure started to drop to close 20 on dash gauge in 5-7 seconds so he shut the engine off
put a mecanical gauge and did the test and read down to 27

so whats thr problem? Warming up opens up clearances? Where? I would of think it would become tigher with higner temps, not loose... suggestion?

Oil thins out as it warms up. Thinner oil = less oil pressure. Should have a bare minimum of 10 psi per 1000 rpm. Probably have some sloppy main bearing clearances. Disclaimer: I am not a Guru.

sloppy like too tight? Or too loose?

Sloppy means loose,,, like sloppy seconds.

did the oil pressure dropped to 20 psi after coming off plane or while at 4500 revs

Also, just to be complete, check oil level, as low oil level can show up at higher rpm as the sump (oil pan) gets sucked dry by the oil pump.

at 4500 after 1-2 minutes
back to normal when running 4000 rpm or less

it was leveled in the morning so i guess it should still be leveled 2 hours later but good point i will ask him

what is normal ? whats the swing from normal to 20

when it start to drop in takes like 5-7 seconds