Roller, stock block, DOVE heads, eagle rods, stock crank, Lenco 4sp., Milodon deep pan. Oil pressure dropping to 20lbs by 3rd gear. Block has restrictors in the crank saddles now. Still have same prob. Have cook one rod and scrapped one crank. Please help.
Sounds to me that you are running the pan dry.
Having say 6 or 7 quarts in the pan when stationary doesn't relate to how much is there when the motor is running!
My suggestion is to increase the oil level by a quart maybe 2.
I have a similar problem with my 460, it has a truck rear sump pan and oil pressure drops on a run as well. I have tried higher and lower oil levels, lower seems better. I thought that maybe the oil is being whipped up by the crank. I have an automatic and shift at 6500 rpm and I have a high volume pump, pressure will drop to as low as 20 lbs. on a pass.
To be safe, start with adding oil. Specifically (and before doing anything), pay close attention to the oil pressure behavior, and then add a couple of quarts and monitor the oil pressure behavior again and watch for any changes in symptoms.
If the problem persists while you feel certain that there is more than enough oil, then try less oil as noted above. Indeed, I had a customer who was experiencing similar oil problems. By watching the oil pressure gage, one would think the oil pump was sucking the pan dry, and he has a 10-quart pan on his engine. Adding more oil didn't eliminate the symptoms, but taking out oil did. Dropping to just 8 quarts in the 10-quart pan seemed to prevent the oil from being drawn up into the windage, thereby leaving a good supply of oil in the bottom of the pan for the pickup. Stranger things have happened...
Ok going to check the drain back holes, and going to add more oil. I'm not the owner, just the one with the ability to be in contact with this Forum. I am member of the www.bigblockdart.com forum. Just found yours today. These forums are great for exchanging info.