I have two motors. Both with the same problem. Ones a 383 with 3000 Miles and the other is a 355 with about 200 miles. Both motors have awesome oil pressure but when you nail it the PSI pegs then comes down to 25 and stays. Both cars have a M55 Pump and 26 spring. Both cars have a miloden stock replacement pan. Oil PSI has also been confirmed on a Matco Oil pressure guage tested behind the intake manifold. You can rev it smoothly to 4000 RPM and have 60+ PSI and as soon as you would nail it to 5000 it comes down to 25 and as you lower the rpms it stays the same till you let off, and as soon as you do and hit the gas again it goes back up. Both shortblocks built by a well known performance shop. I talked with my neighbor whos a tech for GM and he says it could be something inside the oil pump causing this. But whats the chances that I got 2 of the bad pumps for some reason. I contacted melling only to hear that everypump sent out is tested. What can I do now?

 

HI MKos, Melling is correct I have been running there pumps for decades and have never had a problem with them, the only problem wher I have seen this happen is if you have a HV pump and stock 5qt pan, but then it usually keeps droping all the way down unless you let off, but with you having a MILODON PAN that should not be an issue. My guess is that maybe the did not set the pickup depth correct, you need the correct amount of clearance from the bottom of the pan, so when your at idle or you have a slow increase in RPM the oil has enough time to flow into the pickup, but when you hit it WOT then your pick up is restricted, just try to suck air through a straw fast then put it near a table and try it, then try the same with 10 straws and see the difference in volume. I know it sux but you may have to pull the pans and reset the clearance. Also check and make sure if they said they did set it that they brazed the tube to the pump. GOOD LUCK.

 

I had the exact same problem. I ended up installing a 6 qt. Moroso pan. Clearance issues kept me from going w/ a 7 qt. pan. It pretty much solved my problem. My oil pressure still drops when I nail it.........but barely. You're not by chance running solid cam/lifters are you.