I've been searching for an oil burning issue for the better part of a year now (since I put my 350 in), thinking it was a tuning issue or a PCV issue because there's oil in the tube that goes from my PCV to my intake manifold. I have ALSO been searching for missing horsepower for a while.

Here's my epiphany: They are ONE AND THE SAME ISSUE.
When an engine is under WOT, it SHOULD NOT pull any vacuum (maybe 0.5inHg). HOWEVER, when an intake (In my case a stock '86 TPI off a 305) is overly restrictive, the engine tries to get the air it needs elsewhere and will pull vacuum under wide open conditions. I personally have a 350 bored .040" over with double hump heads off of a 69 Z28, a COMP Cams XR269HR camshaft and 10:1 compression, so my TPI is holding back my engine by probably 70-100 horsepower at the crank. With that much of a restriction, my theory is that it may be pulling just enough vacuum to open the PCV and pull oil into the intake manifold. I will be testing this on Tuesday with a spare vacuum/boost gauge a friend of mine has to confirm, but before then, is my theory correct? Could the issue simply be a part matching error that I've made when I built the engine by overbuilding everything else compared to the intake?

@SbFormula just dropping a mention here so I don't chuck another email into your inbox lol

 

The calibration of aftermarket PCV valves is highly suspect. There were different factory part numbers for those on different engines for a very specific reason.

Evidence of excess PCV flow would likely appear in the plenum as varnish accumulation in a short period.

 

It is a bone stock ACDelco part for my 1986 305. While it is on my 350, I have tried to use the ones off of a 350 car before, and even an LS as many people here have said will help, and the issue persists. All ACDelco part numbers. I can guarantee that the oil is coming from the PCV.

 

A restrictive intake should not cause excessive oil ingestion from the PCV system. The more likely scenario is excessive blowby and crankcase pressurization due to rings not seating properly.

 

The motor only has about 6000 miles on it. Just enough for the rings to have seated. And I believe I explained above, that I know it's coming from the PCV because there is an oil coating inside the hose that goes from the PCV to the intake. It's an aftermarket valve cover too, and not an expensive one, so the baffles are likely not quite up to snuff. I KNOW the oil is coming from the PCV, I'm just trying to track down WHY.

 

I would try putting the stock valve covers back on. The baffles (or lack thereof) will make a difference in oil entering the PCV system. If that doesn't fix your issue, then crankcase over pressurization is likely the issue, which will push excessive oil into the PCV system. I agree that in 6,000 miles, the rings should have seated by now, but there are reasons they may not have (and if they haven't by now, they aren't going to).

Machine work, honing, cleaning, measuring clearances and assembly techniques can all be factors in a quality outcome.

 

My 2 cents worth!

I doubt a bit of vacuum at WOT would pull oil that much. If vacuum is present at WOT, the PCV valve will actually restrict flow. I am more on the side of excessive blow by or possibility of vacuum leak from intake gasket.

However, maybe you want to speak with @EDGE . He had a problem with excessive oil through the PCV system. I believe he solved it using an adjustable PCV valve + somehow how the PCV valve was sitting in the grommet.

Check out his posts and maybe try contacting him:

https://www.thirdgen.org/forums/tech...r-baffles.html
https://www.thirdgen.org/forums/tech...d-gm-only.html


Post#19
Just wanted to update. I went with one of those fancy Wagner adjustable PCV valves and the problem seems to have been solved. Before I had 4 to 5 oz of oil in the catch can after 25 minutes of driving. Now I get basically a smear of oil. One thing they mention is to make sure there's at least 3/8 inch gap above the baffle. I had less then that. Valve comes with rubber shims to raise it.

 

 

I have had great luck using the PCV called out in the early LS engines for oil consumption. It is a fixed orifice, small hole drilled in an empty PCV valve shell. Every engine I have used it on practically quits pulling oil into the intake manifold from the PCV system.