Either your pcv valve is bad or you have a vac leak in the catch can system somewhere

Unlikely. The check valve is brand new. It is, however, massive compared to the stock valve. So are the -10 AN lines. If I remove the breather filter and cover the hole with my finger, idle returns back to normal. At the same time I can feel a massive vacuum sucking against my finger.

speaking of the check valve: theoretically when running naturally aspirated, there shouldn't ever be the need for one since the air and blowby gasses only go out through the valve, never IN...?

You can't use a check valve there. Bonafide PCV valve or use nothing and block off the port on the intake manifold.

And so thanks to the collective brain power of MT.net there is scientific evidence that Eunos91 is a moron. Dang.

https://cimg8.ibsrv.net/gimg/www.mia...8f22d22fbe.jpgPCV valves limit flow during idle, are fully open during cruise and block flow during WOT.

Yep, I completely missed the fact you didnt have a PCV. I thought it was just common sense that you could have kept it.

So are your rings just not sealing at all? You shouldn't be able to pull air in through the crankcase.

Rings are supposedly sealing well. Block was bored and honed, and new supertech pistons with Wiseco rings installed. It's not blowby that causes high idle, but rather the improved flow from the inlet (breather filter) through the valve cover and theVC outlet, through the catch can and into the intake manifold. Now that I understand the difference between check valves and PCV valves it makes sense. If I cap the inlet, idle returns to normal.

I will try using a PCV valve from a supercharged Mercedes C-Class

https://cimg4.ibsrv.net/gimg/www.mia...6a6afd424e.jpg

Or run a pcv valve. It closes (or nearly) at idle. Opens off idle. Closes under boost.

Or don't run the passenger side to the intake manifold.

You are running a check valve in the passenger side. What's the point of making that side bigger if it can't do anything under boost anyhow?

edit: I'm way late to this party

Yet another reason both sides of my valve cover go to the catch can and neither goes to the intake manifold.

Not venting to atmosphere keeps polar bears and German TÜV scrutineers happy. Of course I could run both VC lines to a shared catch can, and from there to the intake (pre-turbo). However, I was expecting better vacuum from the intake manifold than from a slash cut right behind my big ass cone filter

william, the check valve was installed to protect the crankcase from positive pressure when my EFR is in

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Maybe something is lost in translation, but what exactly is wrong with my dual catch can setup?

​​​​​​[intake manifold] - [catch can #1] - [PCV] - [valve cover with baffles and copper scrubbers] - [catch can #2] - [slash-cut pre-turbo]

under cruise: a little bit of air enters through catch can #2 path, through valve cover and exits through PCV and catch can #1 along with blowby gasses and acidic waste. There the crappy oil mist is caught, while the air goes into the intake manifold. Active scavenging, polar bears happy.

under WOT: PCV shut, so only passive scavenging of blowby gasses, plus a little help from the slash-cut negative pressure. Any oil that makes it past the baffles inside the valve cover will be caught in catch can #2, before the gasses enter the intake pre-turbo.

I was thinking this is the proper way to do it for a dual duty car that sees both daily driving and track days.

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yeah, forget my current setup. My idle issues result from my misconception regarding the PCV valve (unlike my previous understanding it is NOT a simple check valve but limits air flow at idle as well. My idle issues shall resolve when I receive a proper PCV). Also my N/A is only temporary since I have been waiting for my turbo kit to arrive for weeks and wanted to break in the engine anyway. As stated above, my turbo setup will run a catch can #1 + PCV valve into the intake manifold on the passenger side, and a catch can #2 into the intake before the compressor wheel. -10AN lines all the way.

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@bbundy didn't have any trouble with a block port, its working fine for him. He had trouble with the intake side breather. Under hard turns valve cover would fill with oil and then get sucked out.

The block vent worked fine for him, (and I drilled one on my block). So now he runs a block vent (behind the alternator) And the exhaust side of the valve cover to a catch can. And possibly sometimes an exhaust slashcut. He can explain more if he shows up.

There it is: https://www.miataturbo.net/race-prep-75/should-i-drill-hole-my-engine-block-69247/

i'll try my dual can setup. If it fails, I'll cap the intake manifold intake, dump the PCV valve, and run both VC lines to a t-connector, from there to a catch can and then to the intake before the compressor wheel. Less vacuum, but less complexity at the same time

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Intake catch can helps pull vacuum at cruise and clear out the crankcase. Kind of a street car thing.

Sorry to necro this thread but I'm about to put in a catch can due to not enjoying the smell of oil when I get fully into the boost for more than a couple of seconds.

My current plan is to go for maximum vacuum (even at idle) on the crankcase.

Both valve cover barbs into a Y, into the catch can inlet.
From the catch can outlet, a Y with two lines.
One side to the intake port, with a one way check valve (no PCV).
Other side to the pre-turbo filter area, with a one way check valve (no PCV).

My thinking is that I would pull 20in of vac at idle because there is no way for the crankcase to suck in any air except past the rings.
At boost I will still get decent vacuum in the crankcase because the pre turbo area will provide suction even when the intake is under pressure.
The check valves will prevent any positive pressure from flowing out of the intake manifold and the catch can will prevent any oil from getting into the intake.

Does this seem like it would work as intended or am I just asking for a high idle? There is going to be a decent volume of oxygen inside the crankcase at start, so I figure when I first start the engine it will take a while to evacuate.

Is there any harm to sucking 20-25in of vacuum in the crankcase? My thought is that it would drastically reduce the boiling temperature of any water vapor in the oil and facilitate removing it.