This is a very common misunderstanding.

The only part of the engine that seems vacuum is between the throttle body and the engine. And by vacuum, I mean measurable on your boost gauge vacuum, 20" of vacuum, what have you.

The turbo inlet is simply filtered air. It's at atmospheric pressure. Worst case under full load there will be a VERY small amount of vacuum but you would need a differential pressure gauge to measure it.

Some information -
Intelligent Modification: Measuring Intake Restriction (Part I) | Tuner University

Dale

 

No, not engine vacuum from expanding intake stroke volume and throttle body restriction.

Vacuum from the primary turbo inlet duct being a venturi between the airbox and the primary turbo.

As in how a carburator or compressed air vacuum pump works.

 

If you hook your boost gauge up to the primary turbo inlet duct, you would barely see the needle move off of 0. For all intents and purposes, that duct is atmospheric pressure. Air is drawn through there of course, but the pressure is minimal.

The OMP nipples are designed to just vent. In theory they can just be vented straight to atmosphere but Mazda for emissions reasons has to have anything that could have an evaporative emission plumbed back into the engine's air intake to be burned and scrubbed by the cats.

It's like a plumbing drain in a house, you have to have air behind water or you will have problems draining. Or putting your finger on top of a straw.

Dale

 

Update: Problem seems to be resolved

I did a number of items all at once (not the best way to root cause the problem but it was more convenient to knock everything out together), so I am not sure if it was the combination or one thing in particular. It started with me pulling the OMP injectors to verify I had the correct jets installed in the housings. While doing this, one of the factory OMP lines broke near the banjo fitting. I decided to replace with RP SS braided lines, then did a few other things. Here is the summary:

-New OMP lines. Factory lines looked like they had a bit of oil crud inside of them? Maybe some of this was intermittently making its way into the combustion chamber.
-OMP injectors vented individually to atmosphere instead of being teed into a single line vented to atmosphere. Shouldn't have made a difference but I suppose there's a little less resistance on that side of them now.
-Changed from 10W-40 conventional to 20W-50 synthetic. This seems like the most likely cause in reducing the oil smoke for obvious reasons.
-Ran without premixing. I was only mixing 1/2 oz. per 1 gallon, but I am wondering if the premix could have gone bad? I was using a bottle that I opened new, but thinking back, it was at least 2.5 - 3 years old. I suppose everything has a shelf life.

It's probably the oil change that helped this, but maybe the other items were contributing in some small way as well. Wanted to share instead of having yet another open-ended thread.