And now for something different: Forced Induction Crankcase ventilation systems.

CarMichael Angelo

clearly, I’ve got something going on in that hole
15 Year Member
Nov 29, 1999
Birmingham, al
Something other than the standard topic(s) I guess:

Either I'm plagued with an engine that is destined to have ring seal issues, or my valve cover design has the vent holes right in front of the rocker tips, or oil blowing out under boost is a natural way or the other, I gotta deal with it.

This is a brand new engine with less than a hundred miles on it, so suffice it to say that the rings ( plasma moly) may not have completely seated yet.
Naturally aspirated, ( which it was for 90% of those 100 miles) there was no evidence of blow by even under hard acceleration... But put a turbo in it and......out it comes.

Maybe there's some sort of wonky cylinder distortion due to the fact that all 6 cylinders were sleeved? It'd have to be epic if it was, the wall thickness is now about .180" on all cylinders.

Anyway,...I digress.
I bought a catch can system. one end gets plumbed into the valve cover onto one of the existing breather fittings, the other end gets plumbed into the intake air path in front of the turbo.

My question is this:

Do I add a breather to the valve cover, or do I leave it sealed? If I leave it sealed, I'd be wondering if I'll actually create enough negative pressure in a high vacuum condition to create gasket suck issues. Or do I have to come up with a way to integrate a PCV valve of some sort to allow the engine to "breathe" in high vacuum situations, and then close under boost so that all of the positive crankcase pressure is routed through that crankcase evac system?

In N/A race cars, the belt driven vacuum systems have a small adjustable bleed valve plumbed in to restrict the pull so that gasket suck thing doesn't happen,..

But I can see that by even writing the question, I'm gonna have to find a way to let the engine breathe while in N/A mode.
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Wasn't a pretty sight...and I've got big hands
SN Certified Technician
Mar 2, 2015
The breather I have has a baffle and takes 2 lines one goes to the turbo inlet side and one goes to the valve cover. There's a round breather filter on the top.... drain at bottom. Under acceleration the negative pressure pulls vapors back into the inlet... at idle it doesn't waft vapors. It acts as an inlet for air to assist vapors going through pcv.

My pcv side runs ( when complete ) from intake, through a check valve, sealed oil catch system, and to the pcv valve.


Mustang Master
Aug 18, 2017
I'm n/a now but thinking back to my various supercharger set-ups I always had breathers on the valve covers
and a turbo coupe pcv. Never had any blow-by issues and was anywhere from 5-10psi.
I know there are a lot of opinions on the subject, one way check valves/elaborate systems and those are probably
the correct approach, but my set-up was simple for my simple mind lol and just worked.