I just had the bottom end of my olds redone (twice), I am pretty sure the machinest didnt allow for "looser" clearances, and I spun a bearing 5 minutes into the test run. The pressure never dropped (40-75)until I idled it down to do a basic check for leaks ect. (up to this point I was jazzed !!!!, all the vitals were perfect and it ran GREAT! ) when I shut it down, I smelled burnt oil and the pressure dropped to almost zero. I towed it in and tore it down, all but a few of the rods and mains were toast
So i didn't go back to the same builder, The shop I went to this time has alot of experience with the marine olds motors, lucky for me I shut it down before any damage was seriously done, he ended up mic'ing it/polished the crank, straightlined it, and re-size the rods, I took It out sunday and it ran and did great, but when I shut it down the oil pressure at idle dropped from 40 psi (cold) to 20 (warmed up) at idle, and would jump right back up to 50-60 psi when I accelerated.
I have a standard oil pump in it, and now rather than see what happens I am going to change it out. Mellings has two different pumps one is high "volume", the other high "pressure". Summits description of the "pressure" pump mentions for looser tollerences, but the "volume" pump, would have been my logical choice. I have already installed 2 drainback lines one each side for the oil return from the heads to the pan (hardlined),enlarged and matched the oil drainback passages from the heads into the block, polished the valley, de-burred any obstructions so hopefully the oil can get back to the pan quick enough.
So my question is ......wich pump should I go with, the high pressure or high volume ?