Catch can hose. Why can't I do this?
 

Went to change the oil and have been thinking lately. My catchcan hise only went to pre throttle body. My thinking was under no load there would be next to no vacuume on the house and crankcase. The stock pcv setup is for a mass air flow. I'm speed density. So why no hook up directly to the manifold and always have vacuum on the hose? Idle valve should adjust for any issues and no need for a pcv valve cause there is no maf to meter air. Open throttle or closed shouldn't matter. Ideas? Haven't driven it yet, but is goes to idle fine in the driveway.

Sorry. On my phone. Pic didn't load
https://www.miataturbo.net/attachmen...ine=1444944769

What?

One side of the PCV needs to be hooked up to vaccum, the other side needs to be hooked to filtered air with a breater or by plumbing back to the intake.

With speed density you do not need to pull the filtered air after the MAF.

If you hook both sides of the valve cover to vaccum there is no way to circulate air through the block which is the sole function of PCV, positive crank vent...

With a turbo car with no aux vac pump there is no way to have PCV 100% of the time. There's exhaust slash cuts, but the PCV side of the manifold is closed under load, there's no air for the slashcut to draw from, no flow, no benefit. Just lots of burnt oil in the exhaust.

Edit: what you've got looks fine. The exhaust side VC hole, that goes pre-TB?

Crankcase vent to slashcut to pull vacuum under boost?

Why is the intake side closed?

What about intake side to slashcut all the time.

ALLOFTHECATCHCANTHREADS

If you like oil clouds and woefully under-effective PCV, then slashcut.

The intake side of PCV is closed in boost, mr check valve! If you were to put a slashcut on the other side, it will remove blowby, if that. No more effective than just venting the blowby to the atmo under boost in my opinion. Venting the block when the PCV is open just got a lot harder though, with the fresh air source being plumbed into exhaust and all.

Stock or stock with a breather on the exhaust side is the way to go with speed density.

Slashcut has a check valve so it only pulls vacuum.

What's the best way to pull vacuum under boost?

There is no way other than an aux vac pump or slash cut. Mini coopers run one off the camshaft, but they only use it for wasteate control, not PCV.

I wouldn't worry about PCV in boost, is what I'm trying to say. Regardless, you still can't have PCV without a fresh air source. Trying to hook up both sides to vac leaves no air source for either, ruining the purpose of both.

I think I confused you. Slashcut is pulling vacuum off the intake side. Exhaust is still fresh air.

That reminds me. I need to move the air filter on my exhaust side. Its so oil soaked that its probably a fire hazzard.

I think the mods need to open a subforum for you guys to go discuss catch cans and PCV crap all day. It's absurd how something so simple gets discussed this much.

You aren't allowed in this convo, you've got a catch can on the exhaust breather port while you've totally capped the intake PCV port.

Therefore, you've clearly no idea how fluid dynamics work, and just stick shit errywhere for the hell of it.

Slashcut IIRC from fail's thread works for shit and makes lots of oil clouds. It doesn't pull stong vac, and it makes your car look broken. Why still consider it?

cuz for all we know fae did it wrong? bbundy ran one, might still.

Need to look into what soviet is running.

Did he though, I can't remember.

One cool thing about all these new turbo cars is they all have some wicked heavy shit to go along with it.

https://www.fcpeuro.com/products/vol...FQ6maQodp1cHIg

I'd do that before slash cut. There's other cheaper, probably lower volume, pumps available too.

https://www.miataturbo.net/attachmen...ine=1444948263

This shit looks cheap. Wonder how much vacuum I could pull with it.

I should have added it is not a boosted car. Naturally asprirated. Both cover vents go to catchcan and one hose to intake manifold.

Yeah, that's wrong. There is no circulation if you apply vacuum to both sides of the valve cover.

The catch can goes between the intake manifold and valve cover on the drivers side, to keep the intake from ingesting oil. On the exhaust/passengers side, hook the vent to a breather, or to a second catch can with a breather vent on it.

Then, when the PCV is open air comes through the breather filter, gathers up all the blowby, dumps it in the catch can, and burns off the air used to carry the crap away through the manifold. If you weren't speed density, you'd want to source this air after the MAF like stock since it gets burned all the same.

I don't have a catch can or PCV system on my engine.

I do stick shit everywhere though, that part is true.

Fluids aren't my specialty, but I know the basics. I still say you guys start a subforum for PCV valve discussions!

clearly aidan hates you and wants you to fail

no other reason to suggest something as retarded as slashcut

lol

Read up on what a crankcase vent and a PCV system are. What they are, what purpose they serve, what they improve. They are two different systems. If you're doing something different than how 99.99999% of cars are setup from the factory, you should know WHY you're doing it differently before doing it. That's my rule of thumb anyway.

for whatever it's worth, I think this is a waste of time on an n/a car

Crankcase vent is not optional, blowby is always a thing in normal operation. If you have no crank vent, it will find some.

The sole purpose of PCV is keeping the nasty acidic byproducts from blowby from settling in the oil. Manufacturers have know this forever, and they originally used drag tubes, like a slash cut, for positive crank venting.

EPA say noo! You aren't dumping raw blowby on the ground, you must burn it. This is where the PCV came from, a way to get drag tube like vaccum while destroying the blowby and still increasing oil/engine life.

The unintended side effect is oil ingestion which is fine-ish for 99% of street cars. When you push the envelope, hi-po cars or otherwise, potentially burning oil is a possible engine destroying event.

Thus the catch can, comes stock on some cars, it only need go between the intake manifold and crank volume. If the ECU reads air volume, it needs to know about all the air entering the engine so you must pull post sensing medium. Speed density reads off the intake, thus it reads the PCV air just fine no matter where it comes from.

BBundy, if he even runs a slashcut, understands the benefits of positive crank venting. He's the .1% who should consider a slashcut, because he's always wide open. Street car, or a car ever driven on the street, no. no. no.

I finished writing the PCV subforum!