Jolly Green

Hey guys. Anyone have any experience with a vacuum pump for the Olds 455's? My oil pressure keeps dropping on my 455 during dyno pulls. The shop has checked the clearances multiple times and now they are looking into vacuum pumps to relieve crankcase pressure. Does this work in bringing oil back down from the heads? Anyone read the article in Popular HotRodding about the guy who built a 68 Hurst/Olds clone with a 455 and a Moroso vacuum pump? I just don't see alot of guys having problems with their high hp 455 builds. I even upgraded from a Melling pump to a Mondello and I am still getting oil readings dropping below 30 psi as RPM climbed above 3600. Everyone says its clearance issues but I have had 3 different guys check the clearances and they are always within tolerance. Not saying that isn't the problem BUT I am looking outside the box now. We have the Mondello restrictors in as well to reduce the flow of oil. Edelbrock RPM heads with the drains opened up and smoothed to supposedly allow better oil return.
Ok, so I meant to keep this to just asking about the vacuum pump but apparently airred the rest. So besides clearance issues, anyone have any other words such as oil remaining in the heads or if a vacuum pump is the answer? Thanks guys.

Smitty275

To answer the direct question, yes, I have a good bit if experience with vacuum pumps on BBOs.

Now to help you with your problem. But it'll take a few questions first. What block are you using? How has the bottom end been modified and what kind of power are you making? Flat tappet or roller, hydraulic or solid? What diameter and brand of lifter? How far is the oil pickup from the pan bottom and does it have a bar to keep the bottom if the pan from being sucked up tight? And lastly, have they thoroughly checked the main webs for cracks?

Jolly Green

The block is a 68 455 from a Delta 88. Expecting somewhere north of 500 hp. Stock rods/crank. Custom ground flat tappet cam with hydraulic lifters. Comp cams valvetrain and roller rockers. Stock diameter lifters, that's about all I can remember on those. Oil pan is a 7 qt from Moroso w/ associated pickup. Unknown about the bar or if the webs were checked specifically, but I know it was NDT'd.

Got a call this morning from my friend watching over the engine build at the shop. He said that they are looking to put a lower pressure oil pump in, restrictor pushrods, and rework the heads for better oil return. They are thinkin the heads are holding the oil. Thoughts?

Smitty275

None of those will solve your problems. Did they use Olds lifters or Chevy lifters? Huge difference as one will uncover the oil band in the lifter, which kills oil pressure, and the other won't. When these people say that the clearances are "with-in tolerance", what tolerances are they going by. Just what are the clearances? I run these engines to 7000rpm all the time with standard pushrods, HV/HP pumps, no work to the head oil return holes, and normal clearances. And with only 6qts of oil in the pan. It'll do it just fine with 5qts of oil in the pan but has issues upon rapid deceleration.
What oil filter do you have?

Mr Nick

Can you clear this up please? Sounds like your pressure is above 30 psi at idle and drops as RPM goes up???