[SS Engine Guy]

I'm guessing here but the problem is in the shutdown. Oil pumped to the lifter valley needs to get to the pan some way. On clean neutral systems u won't notice it but with some pans you will loose pressure quickly on decel with the motor still running. How that oil keeps the pick up covered on neg g forces still baffles me. I noticed this when belt drives first became popular as the belt drive cover blocks a little over half of the dr. side hole in the front of the lifter valley and on a big pan would drop pressure under decel. For years I lowered the front holes in factory blocks that Greg is talking about to allow any oil to leave the lifter valley on sbc's because stand offs in the valley were common to keep oil off the crank. I always tried to get any upper oil back to the pan as efficiently as possible by radiusing or lowering any return holes as I'm sure Alan does. Just to keep it off the crank. I know everyone says that the chev engines have great oiling systems from the factory and I agree but I have found some problems that needed to be addressed to make everything just right with different pans and driving practices. Greg, I slot new holes as low to the valley as possible on those blocks and probably bigger than needed. They seem to work better wider than taller.
Its a trick to make sure u have enough upper lubrication but only enough to make parts live. Some stuff works on some racecars but dosen't seem to effect others either way.