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Old 06-16-2013, 02:28 PM   #1
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Default PCV popping out

Question for you supercharger-types...

The current iteration of my intake setup has the stock PCV one-way valve going into a T, one way goes to the brake booster (through the one way valve), and the other side goes to an adapter plate that goes between my throttle body and the supercharger. So, it never sees positive pressure from the intake-side. The other valve cover breather (driver's side) I have capped off.

When I first built the motor, the PCV seemed like it was a really loose fit, so I wrapped the base in a bunch of electrical tape (yes, ghetto), until it nicely stuck inside the grommet. Recently, however, it's started popping out once in a while. The electrical tape is getting gummy with oil, so I could just re-wrap it, but I'm wondering if there's something bigger at work here.

It has a tiny bit of pulling pressure to the side just from the T-line, but that shouldn't be enough to pull it out. So, I'm guessing there's some positive pressure in the crankcase. Would it make sense to uncap the other line, and run a hose from there to my intake (pre-TB) like there is on the stock system?

I've also just noticed that the PCV grommet is replaceable, so I can get a new one of those, but it seems like that's only part of the problem. Figured I should address it all at the same time.
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Old 06-17-2013, 01:54 AM   #2
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What have you done with the breather on the exhaust side of the valve cover?

When a Miata motor is making as much power as you are the stock crankcase breather paths are woefully inadequate. I actually have a -10 AN line tapped to a hole drilled in the side of the block that is hooked into the catch tank/oil separator for my breather system the exhaust side breather holes through the baffles has also been enlarged.
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Old 06-17-2013, 02:09 AM   #3
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At 200hp, I have the stock PCV system intact and it's working wonderful. The intake side goes through the PCV (granted I upgraded to a metal 323 unit) and then into the intake manifold. Maybe you should try moving it to the stock intake manifold location?

My exhaust side is vented to atmosphere through a tiny PCV filter, no catch can yet. I'm just starting to see a little oil residue build up on the filter, might be time for a small can.
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Old 06-17-2013, 02:14 AM   #4
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In the manifold it'll see a bunch of positive pressure. I'd rather not do that. The current position should see the most vacuum of any part of my induction setup, so that should do the most scavenging possible.

I have the exhaust side capped right now. Stock I think that goes into the pre-TB intake tract, so I can pretty easily tap a new line into my current intake tract and hook it up to that. That'd relieve a bunch of stress.

Either way I'm also gonna go pick up a new grommet from Mazda...
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Old 06-17-2013, 06:10 AM   #5
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Yup it sees butt loads of positive pressure. And we all run the 323 valves. And they don't pop out on us...

I'd definitely at least vent the exhaust side to atmo or the intake, to take as much pressure off the intake side.
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Old 06-17-2013, 03:21 PM   #6
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Quote:
Originally Posted by codingparadox View Post

I have the exhaust side capped right now. Stock I think that goes into the pre-TB intake tract, so I can pretty easily tap a new line into my current intake tract and hook it up to that. That'd relieve a bunch of stress.
Pretty sure that is the main source of your problem. The PCV valve won’t flow enough for the amount of blowby you will have in a healthy nearly 300 hp beast.

Another thing is the PCV vent location in the valve cover sucks as a vent. The baffling under the valve cover puts its pickup in the right aft corner of the valve cover. Combine with huge grip and huge power the oil pools up in that corner of the head when you accelerate hard out of a left hand turn. I have verified this for myself by pumping out nearly a quart of oil out the pcv vent hole during a track session with it hooked directly to a catch can. Flog it all day on the street without the cornering G's and it doesn't do it. What happens with the PCV in place is You will periodically get a big slug of liquid oil trying to go through the PCV valve It chokes it up and it slows gas flow so much you build crankcase pressure in a hurry. The exhaust side vent is baffled to right in the center of the head oil doesn’t pool up there. It is a much better crank case vent location.
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Old 06-17-2013, 03:34 PM   #7
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Yeah, I'll be giving that a shot tonight.

Just picked up a new grommet for the passenger side one on the valve cover. I guess that's what they're supposed to look like. My current one has hotdog-in-hallway syndrome. This should be a nice improvement.
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Old 09-15-2013, 02:54 AM   #8
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Quote:
Originally Posted by bbundy View Post
Pretty sure that is the main source of your problem. The PCV valve won’t flow enough for the amount of blowby you will have in a healthy nearly 300 hp beast.

Another thing is the PCV vent location in the valve cover sucks as a vent. The baffling under the valve cover puts its pickup in the right aft corner of the valve cover. Combine with huge grip and huge power the oil pools up in that corner of the head when you accelerate hard out of a left hand turn. I have verified this for myself by pumping out nearly a quart of oil out the pcv vent hole during a track session with it hooked directly to a catch can. Flog it all day on the street without the cornering G's and it doesn't do it. What happens with the PCV in place is You will periodically get a big slug of liquid oil trying to go through the PCV valve It chokes it up and it slows gas flow so much you build crankcase pressure in a hurry. The exhaust side vent is baffled to right in the center of the head oil doesn’t pool up there. It is a much better crank case vent location.

I just got back from the track. I think I'm having this problem. I have a 323 GTX PCV in the stock location (intake side) and a catch can on the exhaust side. I've pumped out a pretty decent amount of oil in a session or two. I have oil coming out of the valve cover gasket as well and I think some more oil coming out my turbo return at the oil pan. I think the culprit in general is crank case pressure. However it seems that it does this while not cornering too... I remember it was pushing a little oil out the exhaust vent it during my tuning session.
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