PCV/catch can setup for a street car
Hi guys,
I know there's a bit of info on the forum in relation to catch can setups. I've found Jason's thread where he has measured the pressure, as well as another fairly long thread. They all seem to be a work in progress. Anyway I daily drive my MX-5 but also use it for track days. I am currently only running wastegate boost but I want to be able to run up to 18psi eventually as the motor is fully built. I am already having turbo to manifold stud backing out issues at this boost level but that's a different story. Here is my current PCV setup: https://www.miataturbo.net/attachmen...ine=1358401727 Notice the catch can tucked under the suspension tower brace, then feeding back into the intake: https://www.miataturbo.net/attachmen...ine=1358401727 It seems to work OK for now, but I am assuming this will be an issue when power and boost levels are raised. Do you think there's any point in all or any of the following?
Thoughts? |
No thoughts, but that engine bay is pretty clean, and setup look good as well.
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i put my catch can between the PCV and intake manifold.
on your case the catch can only catch fresh air from the intake not the oil vapor. |
Did you add any baffling to that can? I have the same one sitting at home that came off my last car and hasnt made its way into the miata yet and I went through 3 variations of baffling before I got something that worked really well.
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It is filled with steel wool but that is all.
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You might want to switch to bras wool, especially if you switch to can to be on the pcv line. The brass wool is much less likely to break up and get sucked into your engine.
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why do you think you need to do anything different/special?
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I think your setup looks decent. Are you collecting oil in the catch can? My favorite catch can setups have both a pre-turbo "suction" pipe (which you have) and a drainback outlet for the can into the crankcase.
Oh and yes, I'd ditch the PCV. PCVs are for emissions not power. They also have the potential for letting boost into the crankcase and blowing engine seals. |
Originally Posted by AlexL
(Post 1002693)
Oh and yes, I'd ditch the PCV. PCVs are for emissions not power. They also have the potential for letting boost into the crankcase and blowing engine seals.
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I know I know but the stock miata PCV is made to be open at WOT and let crankcase fumes be pulled out and burned. Is it rated to hold back 20+ lbs of boost?
Or an inline check valve, yeah those work too :brain: |
the stock PCV is not made to be open at WOT. the plunger just doesn't always seal well. I'm still using a stock PCV with an inline check valve.
I don't lose a drop of oil, infact I'm pretty sure when I do oil changes I drain more than what I put in. |
Originally Posted by Braineack
(Post 1002722)
the stock PCV is not made to be open at WOT.
From wiki:
Originally Posted by Wikipedia
At idle, the intake manifold vacuum is near maximum. It is at this time the least amount of blow by is actually occurring, so the PCV valve provides the largest amount of (but not complete) restriction. As engine load increases, vacuum on the valve decreases proportionally and blow by increases proportionally. With a lower level of vacuum, the spring returns the cone to the "open" position to allow more air flow. At full throttle, vacuum is much reduced, down to between 1.5 and 3" Hg. At this point the PCV valve is nearly useless, and most combustion gases escape via the "breather tube" where they are then drawn in to the engine's intake manifold anyway.
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WOT means massive amounts of boost, which means the boost overloads the flimsy little spring and the plunger seals up against the back of the valve. PCVs are designed to close in boost and during backfires.
the pcv is pretty much a check valve, the only issue being they dont always seal so well. so you add a check valve that does, then the pcv can work in normal operation and boost will absolutely not creep past and pressurize the crankcase. the miata engine needs nothing special for low-boost setups as far as im concerned. |
is 18psi considered low boost?:party:
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Ok I just misunderstood you :hustler:. I agree with everything you just said.
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Originally Posted by 18psi
(Post 1002748)
is 18psi considered low boost?:party:
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So what's the solution? 1-way check valve or just gutting the PCV entirely?
ASSuming one doesn't have any need to pass emissions and is running an aftermarket ECU, is gutting completely the preferred way? |
well if you gut the pcv, youll idle at 3K.
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if you don't care just don't do anything. route the vc breather to atmo on the exhaust side, and leave the intake side the way it is.
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Originally Posted by Braineack
(Post 1002774)
well if you gut the pcv, youll idle at 3K.
.... Or a retarded BP thing that i've never run across on any other car i've ever owned. Maybe i should clarify: By "gutting" i mean removing the valve, running from that location to a vented catch can, not running back into intake.
Originally Posted by 18psi
(Post 1002775)
if you don't care just don't do anything. route the vc breather to atmo on the exhaust side, and leave the intake side the way it is.
Doubtful i'll ever run anything more than 17-18psi on my BP car, so i'm likely overthinking this? |
Originally Posted by concealer404
(Post 1002776)
..... not sure if trolling....
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Well I mean, the pcv is kind of already fully open when the manifold is under vac and closes as the manifold pressure becomes greater than the pressure in the cylinder head.
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Not true. It's fully open the closer to atmospheric, with more vacuum the plunger reduces the flow as it's sucked up against the inlet. it only closes completely with boost.
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Originally Posted by Braineack
(Post 1002781)
you're not sure im trolling because im suggesting if you open a huge port to atmospheric on your IM, behind your TB, you will idle at a very high RPM?
My simple question was whether or not that'd be stupid on a BP that won't see more than 18psi at the most. If i want to go over that, it'll be on a built motor and i'll re-visit the subject at that point. :party: |
Originally Posted by Braineack
(Post 1002781)
you're not sure im trolling because im suggesting if you open a huge port to atmospheric on your IM, behind your TB, you will idle at a very high RPM?
What about the MSM PCV? |
Originally Posted by vitamin j
(Post 1002791)
I think he means capping it off lol.
What about the MSM PCV? Hence the questions. :makeout: Is the MSM super awesome or something? I know on other motors we used to snag the 323GTX PCVs because they held up better under boost in theory. |
Originally Posted by concealer404
(Post 1002789)
I'm a little offended that you think i'd be stupid enough to not plug that hole. IF i do this, it will not be the first time i've removed a PCV system entirely. But previously that was on motors ingesting well more than 20psi of boost. (WAY overfilled, you know?) :giggle: Or on a motor that no longer had an intake manifold.
My simple question was whether or not that'd be stupid on a BP that won't see more than 18psi at the most. If i want to go over that, it'll be on a built motor and i'll re-visit the subject at that point. :party: most people here will plug that hole and weld a second bung on the other side where it has better baffles. |
Originally Posted by Braineack
(Post 1002793)
:)
most people here will plug that hole and weld a second bung on the other side where it has better baffles. So that answers that question, but is this something that would be overkill and more work than it's worth to do on a "mid-boost" MSM? (I'm not sure if that qualifies as over-filling.) |
I'd just let the factory catch-can do its job.
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Originally Posted by concealer404
(Post 1002792)
I have an MSM with an upgraded turbo that's about to get tuned @ 15psi or 250wtq, whichever comes first.
Hence the questions. :makeout: Is the MSM super awesome or something? I know on other motors we used to snag the 323GTX PCVs because they held up better under boost in theory. |
Originally Posted by Braineack
(Post 1002799)
I'd just let the factory catch-can do its job.
There's some issues with the factory catch can and how terrible it is, but for my street car, not likely to be a problem. |
i mean, the same can be said for the MSM turbo setup and ECU alone... so.
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Originally Posted by Braineack
(Post 1002806)
i mean, the same can be said for the MSM turbo setup and ECU alone... so.
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