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!

Right, which is why I think OP can easily just stick w/ stock

Stock setup with a catch can to avoid blowby being picked up, it'll catch what little you'll have move and not screw up normal operations.

Here is the current deal. I was an idiot and wasn't thinking with what I did before. Vent filter on exhaust and intake side goes to catchcan and catchcan goes to intake. Maybe not perfect, but it should suck the poison out now.


https://www.miataturbo.net/attachmen...ine=1444961254


Yes i need to loom the harnes and etc. Still a work in progess.

No, before you had it right. Now it's wrong.

EDIT: misread his post

I don't know, sounds like he had it right all along. Vent filter on exhaust, can between intake and pcv. There's only two lines on the catch can, so the exhaust side can't be hooked up there too.

It's pretty perfect for a street car!

Before both valve cover hose did a YY, connected together, and then to the catch can and then to intake. No flow only vacuum. Now air can flow through and go in pre throttle. I after the throttle would piss with idle as it would be a massive vac leak. Both in a Y under vac only idled OK ish.

It's not a massive vac leak though, it's a steady controlled crank cleansing stream that can be compensated for. The stock PCV valve is designed and sized accordingly, and it works stock.

At least that's how it should be, the catch can hooked up post-TB to the stock PCV hose port on the intake manifold.

What you've got now sees no vacuum most times. That would be a much better location for the exhaust side vent, if you didn't want a breather filter.

I have a slash-cut. Works well. Order of operations is :

Fresh Air > Moroso filtered VTA catch can (intake) > AN10 to Valve cover > ENGINE > AN10 to sealed Mishimoto Baffled Can > Vibrant Check Valve > Vibrant Slash Cut.

Sooooo Slash cut pulls vacuum, Fresh air comes in from Filtered VTA can, no nonsense in my intake manifold.

Car is NA right now, but will be turbo soon. The way I figured it is that as volume of exhaust gas increases, so will vacuum being pulled. Should work well when needed in boost/full throttle.

Do you have data on how much vacuum it pulls?

Nope. Not yet at least. Would like to get some data from it, but priority has been getting trubo going. :likecat:

Now it won't idle below 1200rpm. Even with the idle valve closed. I think it is the stock style route with out a pcv valve. Just don't have one here is all. Vent filter on the exhaust side. Starting to think a VTA would just be easier. I just wanted to suck the nasty out of the crank case. Most things I've read say vacuum on the crank case is good.



https://cimg8.ibsrv.net/gimg/www.mia...29288b6f79.jpg


This has no real vacuum under low load and idle.




https://www.miataturbo.net/attachmen...ine=1445203104


This I think is basically how the factory route is. EXH side goes pre throttle/post filter, intake valve cover port to catch now to intake mani. Won't idle even with valve closed and spaz idle. I imagine the stock PCV introduces enough restriction maybe to idle or I'm all screwed up.

Vibrant slash cut? I'm going to buy one and put a map sensor on it.

If vacuum is the important bit hen why not run both valve cover vents to the catchcan and then to the intake mani? No pre throttle post filter? Been reading through threads and so many pissing matches. I seems getting rid of the blow by crap is the the big issue. I'd think some air flow would be required for that, but I'm guessing the "flow" is from the continual addition of blow by gasses. Not from an outside source like a VTA filter. Stock both sides are on vac of one sort or another.


https://cimg2.ibsrv.net/gimg/www.mia...e09597878e.jpg


Always vac.

Pulling vaccum is cleaning out the crank case and pulling in cleab air. This won't work when under boost.

Just bought a slash cut to try out and see if it actually pulls vacuum.

They work at high load VERY well. Very common on circle track cars I watched when I was younger, everybody ran them to pull a vacuum on the crankcase for extra power. Those usually had them right at the collector of the headers with a 5/8" or so hose hooked to it.

Do these pull significant enough vacuum? Seems like this would be a really nice solution. Just run the passenger side valve cover hose to a can, and the other end to the pump. Keep your intake nice and clean.

Because there is no flow.

I don't know what's wrong with your car, but if it won't idle with a stock PCV setup with extra catch can something is terribly wrong.

Anything other than stock with a catch can is a waste of time. Normally one side is on the intake at vac, and the other is at ambient pressure to introduce flow, it can be vented to the atmosphere if no MAF. I am not saying this again.

I don't know, but it's not a PCV pump but a brake booster pump. I imagine it puts out a massive amount of vac at a really short duty cycle.

I agree that it needs vacuum, deezums. For anyone else disagreeing, do you have any long term results to show for anything else that doesn't use a vac source (at least for a street car)?

I posted my HF/PrimeFit can in another PCV catch can thread but I can't find it now. I recently took a look of the inside of the IM (on my other car) that has had a Husky can between PCV and IM since 2007, about 50k miles later, it is not that much dirtier (wish I started with a brand new IM). I can post a pic before/after but it is not a Miata manifold.

I think part of my issue was no pcv valve to restrict flow.

PCV valve is indeed needed. It actually closes at idle, and, if the right one, again under boost. It only flows in between.

Either use a 323GTX turbo style PCV, or stock valve with added check valve. I don't think it matters which side of the catch can, but if between the can and the valve cover, the can will see boost.

+1 for the 323 GTX PCV with a check valve

Run a quality can on each side. On the pass side run from the pcv or chk valve to the can then to the intake manifold orig. spot. On the dr side run the line from the valve cover to another closed can then to the intake tract somewhere behind the kn filter Not the bottom of the filter. The highest vac is idling which is drawing a vac through the pcv [which does not completely close in that direction] or chk valve. The air source is from the other side being vented into the intake tract which has very low air flow going on. As revs increase and vac decreases the pcv or chk valve starts to close and when closed at high rpm's the air hauling ass past the hole in the intake tract well create a vac., but that line needs to be plumbed into the hose and not the bottom of the filter to create the vacuum. The same thing happens but even better when FI as when in boost the valve closes and the air in the intake tract is really hauling creating even more vac then when NA. I just bought 2 Radium engineering catch cans and this is the setup I am going to do.

May I ask why you feel this way?

I have an n/a track car on sticky tires. After high-G, left turns (Laguna Seca T, T6, T9) I get a lot of blowby smoke. Meatball flag ensued.

Then mod your valve cover so that it drains and filers better.

Or do this. I made a turn-up of the breather port, so that it breathes from oboe the oil puddle.

https://www.miataturbo.net/attachmen...ine=1452540115

How so? I read this thread and so many others that my head is spinning, with lots of conflicting information...

Better yet, pull from the driver side vent instead, bUT that the one yout need to enlarge the vent hole on, aND add finter media.. Don't use the other one, where the oil pools.

I did both of them, but I'm 97% sure that my bent breather would have solved everything. Of course that's because it was my idea.

I would think that you'd be getting a different color flag if you're turning left at T4 :giggle: :rolleyes:

My phone posts are horrible.

:facepalm: Agreed (and fixed)!