Hello, I am working with a B18c1 head/ B18a1 block. The connection between the air intake tube and the valve cover provides "fresh" air into the head to force or replace oily air leaving the engine through the PCV.
When will the pressure inside build to the point the "bad" air tries to go back up the tube and into the air intake?
I am not refferring to the normal oily air that goes into the intake manifold to get re-burned. I am concerned with the hose from the valve cover/ air intake tube.
I want to know if it is useful to put a one way check valve in the tube to prevent the "bad" air from trying to go back up into the intake tube? Maybe use a "Y" connection right at the valve cover nipple - good air can come in but bad air is shunted to one of those little stand alone filters??
Does this idea have any value? I will have an oil catch can between the PCV and the I.M. return, so I am thinking all "bad" air should be annhilated.
Thanks. RFT

 

It depends on how much blowby you get past your piston rings. So it's not an exact point, but it's at higher rpm & more-open throttle. Whenever the amount of blowby exceeds the amount sucked out thru the PCV, then the flow reverses in that vent line.

You could put another catch-can in that vent line. If you use a check-valve you risk pressurizing your crankcase - not good.

 

What do you think of the "Y" idea with reversed check valves at the "Y". The "Y" fits right onto the valve cover hose barb? The "good" air line is open one way inward draw; the back pressure is handled by the reversed check valve into a catch-can??
You know where I saw a "Y" vacumn tube? On the back side of the intake manifold for a B18c1. There is a "Y" connection splitter.
I know you will say "put the dirty air hose up your nose!" haha. I am going to try this. Little check valves are inexpensive, or maybe I should go to the junkyard and cut out some booster cable check valves - they are one way, right? Thanks.
OK, I'll just go out and inhale the bad air now.........

 

"Put the dirty-air hose up..." ummmm... nevermind
(JK)

Yeah, that sounds good, except for legal EPA emmissions stuff. Plus the restriction of the outwards-pointing check valve. That won't be completely free-flowing, there will be some restriction unless you get a fairly high-capacity check valve. Maybe a brake-booster valve will be OK? Then you still gotta worry about the check valve sticking closed.

That collection of Y-fitting, check valve, & catch can has to be pretty low restriction so you don't pressurize the crankcase.

 

ok thanks. rft