I've searched for a while, now I think I am more confused. Here's my issue. I have a 383 with a novi on it. Normal driving its fine, but under boost starting around 3 psi, it blows oil out the dipstick and some out the breather. I capped the dipstick to avoid a fire, but I still get some out the breather. I do have a good check valve now instead of the junk aftermarket pcv valve after it blew out the rear main seal. That still leaks some just need the time to fix it. I need to do something different to fix this issue. Currently I run a pcv/check valve/intake from the drivers side vc and an open breather on the pass side. I tried from the pass side pcv/catch can/sc inlet but that seemed to make it worse which really does not make too much sense. I measured vacuum from the dipstick tube and at idle or revving it, it remained at zero with no change. That was with pcv and open breather. For the heck of it, I put a pcv valve in the pass side replacing the breather without any hoses on it. It now builds around 5 inches of vacuum at idle and decreased some as I revved it. As I am typing this, I realized I should have seen what the intake vacuum was, but my guess its higher. It also ran rougher than normal this way. My thinking is that there should be some vacuum, that my pcv may be a vacuum leak through the breather and I tuned around it. I was also thinking about adding an lt1 smog pump to run under boost. Free mod for me. I guess I just need some guidance from the gurus on what to do next. Thanks and sorry for the novel.

 

I hate to tell you this but you need rings. I would take it .010 over where it is now get some nice dish pistons for supercharging and some total seal rings.

 

Yeah rings are shot, or there is bore taper or both.

I run file fitted top and 2nd rings and ultra low tension oil ring on my 22:1 compression diesel which regularly sees over 10psi of boost and it don't spit any oil or have much blow by once its warmed up.

 

This motor has roughly 500 miles on it with total seal rings and 8.5-1 compression je pistons. I paid a great deal of attention to file fitting the rings and having a machine shop ensure the bore was straight and finish was right for the rings. I've read too many horror stories about total seal rings and finish issues to not make sure that was wrong. IF it was the rings, wouldnt it burn oil most of the time, not just a very little on deceleration after a hard run. I guess a leak down test would answer the question but I have a feeling that will be OK. I have read others having this particular issue. They ended up using a vacuum pump in the end which may be the way i will go. My question still is though, what should be the normal amount of vacuum in a crankcase under normal conditions.

 

I would say none, no vacuum. The one valve cover is vented to the intake tube, with the other having a PCV valve. Any vacuum applied to the PCV valve will cause air to be pulled in via the vent tube.

There are other areas that can pressurize the crankcase when in boost. Such as an intake manifold gasket leak into the lifter valley.

RBob.

 

Ok that makes sense.
My engine had more blow by when it was new for the first several thousand miles than when it had 230,000 miles. There was so much blow by those first miles I thought I screwed something up.
I also didn't have a turbo on it back then.