I have a 355 sbc I had rebuilt last year and went to a car show this weekend and checked oil before I left and had 70 psi oil. On my way back from the weekend it dropped to 40 psi. I have a high volume oil pump and this pretty heavily mild- built.

My thoughts are either I'm not getting enough vacuum to my crankcase or my piston rings aren't doing the job. I had this rebuilt before because my rings never seated. Any suggestion? Also the oil is pretty black and has a burn-your-eyes effect when idling and blows black smoke and loses power @5600 rpm.. When it should be peaking around 6000.

The oil pressure has nothing to do with the oil level.

What would explain my drop in oil level then? Everytime my psi gets low, so does the oil level

You have a bad intake gasket? I know this was a common problem on 5.9 Dodge motors and it resulted in fouled oil and heavy oil consumption. (I know this is a Camaro forum and you're talking about a SBC I'm just using the 5.9 as an example)

How much oil did it eat? And an easy way to check for the sucked intake gasket is pull your PCV tube and feel for vacuum at the hole on the valve cover.

It doesn't surprise me the oil pressure dropped. An engine does lose a little after it warms up but 30psi is a little extreme. Is it the factory gauge or an aftermarket one? Because the Factory gauge will pretty much just tell you you have oil pressure or not, it's not very accurate.

Doesn't oil psi rise and fall with rpms?

How are you checking you oil level?

Burning eyes and black smoke is a sign of an obscenely rich mixture. I'd deal with that before any oil-burning issues.

It's a fairly new intake gasket? Idk if that's a problem but I'll check. I have an auto meter gauge. AFR reads more lean than it does rich.

Oil psi normally rise 10-20 psi when I'm driving regardless of what the psi is at idle. But I know one time it got to 10 psi and didn't change much. I'm checking Oil on the factory dip stick. But if my rings aren't sealing, gas and oil are going to mix, but I have no blue smoke so idk. That problem might be my 6.5 powervalves as far as burning the eyes