Helped run a 632 on the dyno the other day. We only got one shakedown run before we had an oiling issue. We think it is windage related, not sure. The engine starts to lose oil pressure after running for a while and it only recovers if you shut it down and let it sit for awhile. Could also be a sticking relief valve or something like that. We couldn't debug it on the dyno so the guy had to pull it off and take it back to the shop.

Could berelief valve or poor oil return something some of the big chief style stuff is known for. Also having the vacuum pump hooked up is not going to help that. Not unusual for us to have to add extra oil on the dyno. Be curious to see what he finds, the SB in the Vette we have to run a couple extra quarts in it, just does not seem to like running on the dyno in a static position, in the car we go back to 6qts with no issues, I know crazy.

Very nice! I'm building a 475" BB Chevy right now for my "shop truck".

Is the distributor shaft seated correctly?

Some of them have a slip collar and the shaft moves up or down too far and won't let oil pass correctly there.

We took the belt off the vacuum pump and that helped with the oil pressure. We were able to make a full pull on the dyno but when we finished the pull the oil pressure dropped way down at idle so we shut it off. This is the second time on the dyno. The first time the valve covers filled with oil and we couldn't make a pull. He added drain back hoses and had a new pan built. Those changes fixed some issues but it still isn't quite right. We had 8 qts in a 7 qt pan which might have been too much. We didn't want to run it low since we knew the valve covers would hold oil. I suppose we could've tried higher and lower oil levels to see if there was a solution.

Don't you just love custom made high end race parts that haven't been thoroughly flogged to get rid of the problems they create
I remember doing R&D for Bill Hayes on his ignition boxes, patience is the key to fixing some of those problems

What oil pump/bypass spring, and oil restrictors?

I've struggled with a few BBC with billet pumps that just moved too much oil upstairs for the pan volume.

This is the last 632 I ran on dyno

We had that issue w/ a Dart block small block a several years ago. We tried a billet Melling oil pump and it pumped way too much oil up top...starved the bearings. Went back to a regular HV pump and no more issues.

That could be the problem here too. But it is a bunch of work to change oil pumps on an engine like this so it is slow going. Engine has to come off the dyno, get flipped over and the pump changed. Then everything has to dry before it goes back on the dyno. Costs add up quickly when chasing problems like that at a dyno shop.