So, this is a 350 (+.040) BUICK motor in my 1968 Buick GS California. I had a local builder reman a viable 1972 long-block, as the car had no motor/trans when I bought it. I spec'd the cam, as Comp was doing custom grinds for the same price as off the shelf. It's basically an XtremeEnergy flat-tappet 268H with 112 lc to be a bit more EFI friendly. Stock rockers (new), stock pushrods, etc. It is NOT EFI at the moment, but that has nothing to do with the problem. The rebuild was fairly straight-forward, just a cast-piston street motor. He did work the heads over and was able to fit 2.0" x 1.55" valves along with some light porting and clean up. The engine runs great and is probably one of the strongest street 350 Buicks around. It dyno'd at 352hp (crank), and the most they put out stock was 280.
The oiling system is essentially stock, other than an upgraded TAPerformance front cover/oilpump assembly. After it was dyno'd, I brought it home, put it in the car, and it was turn-key, ready to drive. Drove it real easy for 150 miles and then started getting into it more. The car went away for body/paint and then upholstery. I got the car back and noticed the oil pressure almost ZERO at idle. I don't honestly know when it started creeping down - or if it did it all of a sudden. Anyway, I contacted the builder and he said there was no oil problems on the dyno - I wasn't there for the dyno run. I was running 10/30 Valvoline with a Fram filter for the first break-in oil that I was running after the dyno oil. He said to put an STP filter on it and run some straight 30 oil and see what it did. I did that and there was no change, other than a TAD higher initial (cold) pressure. It originally had the stock oil pump with a HV kit (spacer plate and longer gears), so I ordered the WHOLE front assembly from TA just to see if that changed anything. It didn't. Same as before.
Basically, it starts cold with 60 or so oil pressure. Then jumps down to 20-ish. After a few street miles, town driving, the oil obviously warms up and it drops to 3-5psi at idle, 18-22 at cruise (2800-3000). At idle, the lifters DON'T bleed down at all. There is no racket from the motor. It is quiet and smooth. 180 thermostat, alum radiator, electric fans, never gets over 190 (temp that the fans come on). No oil cooler.
Finally took a vid and want to see if anyone here has any ideas. I've NEVER had a motor do this. It now has 20/50 Valvoline, K&N filter. The pressure has not changed with ANY of the three filters I have tried. The 20/50 has been the best oil pressure yet (no big surprise), but I am just amazed how it starts off great and immediately settles down. Just watch the vid and let me know any ideas you guys have.