The definitive "How do I catch can?" thread.
 

Hey guys,

I see threads all over on this forum and others about catch cans, and it seems that most people don't know how the stock PCV system works, and thus don't know what the fuck they are doing when then install a catch can system.

The purpose of the stock system is to allow filtered air to be sucked in from the crank case vent, through the head, down into the crank case, and out through the PCV valve into the intake manifold where the nasty shit is sucked into the combustion chambers and burned (putting you closer to knock in the process). The reason we have this is because even in a good engine some gases from the combustion events make it past the piston rings and into the crank case. These gases if left in the crank case form acids in the oil that cause corrosion and bearing wear.

Keep this in mind and it explains how to route things for a correctly operating system while using an oil catch can. Either that or just look at the diagrams :)

A normally aspirated engine doesn't really need a dual catch can setup, you can have a bit of vapor venting out the inlet vent side at WOT even when naturally aspirated, but not very much... with forced induction you will have a bit more venting from the inlet vent side under boost, and may benefit from the dual catch can.

https://www.miataturbo.net/attachmen...figuration-jpg

https://www.miataturbo.net/attachmen...-can-setup-jpg

https://www.miataturbo.net/attachmen...-can-setup-jpg


Keith


PS: Never put the oil from a catch can back into your oil pan, the better your catch can works, the more of the acidic crap is trapped in the oil in the catch can. I had a catch can on my EVO that I stuffed with steel wool, and the shit that came out of it was a horrifying mix of unburned fuel, water, and oil.

Why are you pulling crank case vapours into the combustion chambers on purpose?

Can I just built just btw. Inlet manifold nipple has a hose as you can see on the second pic (just make it out its under the cam cover one) and its blocked at the end, hose rather than nipple just for aesthetics.

https://www.miataturbo.net/attachmen...ine=1396404265

https://www.miataturbo.net/attachmen...ine=1396404265

Dann

The purpose of the PCV system is to allow the negative pressure in the intake manifold to apply vacuum to the crankcase.

The purpose of a turbocharger is to apply positive pressure to the intake manifold.

Think about that.

There are no "in" holes in my valve cover. Only "out" holes. "In" holes in the valve cover are only there to keep the Californians happy. Even in a stock car, the natural flow of both of those holes is "out" at anything other than an idle.

Lastly: there had better not be any filtered air in my crankcase. If there is indeed air (which contains more than trace amounts of oxygen) in my crankcase, it's because I have positively ventilated the crankcase.

With a properly setup catch can with filter media in it you aren't, the water vapor, oil vapor, and fuel vapors condense out in the filter media and stay in the catch can. The stock system is set up to burn this stuff because the EPA frowns on venting that noxious crap to atmosphere.

Back in the 60's and before, cars had a passive system where crank case gasses were just vented out under the car via a hose. The gaseous stuff vented to atmosphere and the oily gunk dripped on the ground under the car.

The current day stock system is an "active" system that does a better job of getting the crap out of the crank case using the negative pressure in the intake manifold to suck out the crap, and the vent tube that goes to the stock intake track to allow fresh filtered air in. It makes the EPA happy because the noxious crap goes to the intake manifold and is burnt in the engine. This makes performance enthusiasts sad because this noxious crap is perfect for lowing your knock threshold, so you can't run as much boost and timing for the same octane fuel as you could without this crap going into the intake manifold.

Keith

Interested to see where this goes. Subbed (on phone).

And the PCV valve is a check valve that keeps the positive pressure in the intake manifold from pressurizing the crank case!

When the car is in positive boost, the PCV valve is shut and any pressure build up in the crank case from blowby getting past the piston rings goes out the vent on the drivers side into the intake. This is why a car with a forced induction system can benefit from a second catch can, it prevents the noxious crap from the crank case from coating the insides of everything in the intake track, and keeps those same vapors that don't condense out in your intercooler from making it into your combustion chambers.

If you take any factory turbocharged car and take the intercooler off and dump some mineral spirits into it as a solvent and shake it all around you get black oily goo out when you dump it. This coating of crap reduces heat transfer as well as all the other nasty effects.

If you just have an out hole without any in hole you have a 60's style setup with poor ventilation. You can do a "vent to exhaust" setup if you do a venturi in the vent line where it joins the exhaust to allow the exhaust flow to draw a vacuum on the system. This is more complex than a PCV valve system, and the vacuum isn't as strong... but it is better than the passive 60's style setup, and in some ways is better for a forced induction setup since it has good vacuum even when the engine is under boost when you need it the most.

Keith

Let me get this straight, in boost, when your engine is producing the most blowby, we are intentionally halving the flow capacity of the PCV vents, in order to slightly improve the vac on the PCV when out of boost, and still feed the engine low octane gases?

You have zero vacuum when under boost, so you don't have "active" scavenging of the blowby gases... but they still are vented "passively" through the vent on the drivers side. And as soon as you go out of boost into vacuum in the intake manifold the PCV valve opens and draws all that crap out and into your catch can. Even on a track day event, every time you shift the PCV system is actively scavenging this crap out of your crank case, and when under boost it is passively venting out the vent side.

In the mitsubishi world, poor PCV operation results in oil dip sticks being blown out of the dip stick tube by the positive pressure in the crank case... this is common in two circumstances, a poorly executed catch can setup or a failed PCV valve that allows boost pressure into the crank case.

As a rule of thumb, if your dip stick is staying in your dip stick tube, then you are not building up significant positive pressure in the crank case :)

Keith

Apparently the above message is too short so I had to type this.

https://www.miataturbo.net/attachmen...ine=1396411571

Dude stop explaining how a pcv system works. What these guys are saying is why would you want shitty vacuum when you need it most (under boost) in exchange for decent vacuum it idle/low load.

Because it is better than no vacuum ever? As long as you still have the drivers side vent, and you don't have massive blowby or a leaking PCV valve there is never a positive pressure buildup in the crank case, so there aren't any problems due to over pressure.

With a passive system, you don't have vacuum under boost, or when not under boost... if you are satisfied with a passive vent system then have at it and enjoy!

Personally since the drivers side vent is large enough to prevent positive pressure in the crank case I see no reason to disable the PCV system when installing a catch can setup. The benefits of keeping the PCV system intact become clear when you have a two catch can system and see how fast the can on the PCV valve side fills up when compared to the can on the passive vent side.

Keith

tl;dr

I think you (OP) are confusing a separator with a catch can. Catch can catches the bullshit. Then you dump it in a solo cup every once in a while or forget about it and it makes a sexy oil explosion in your engine bay.
Separartor does the same thing but with less maintenance at the cost of effectively lowered octane when your busted ass engine blows tons of oil vapors into the intake manifold.

The idea is to take a vacuum from somewhere else, be it intake tract or as you mentioned earlier from the exhaust will give you negative pressure in the crankcase at all times but also increasing with load/boost. The idea of negative pressure in the crank case is not only to evacuate unwanted fumes but also vacuum helps your rings seal better. Less blow by, more power, happier engine.

Also regardless of how good you "filter" your catch can with steel wool pot/pan pads or shower lufas or whatever its not an air filter and its going to still dump blowby fumes into your intake manifold.

I have a solution:

https://www.miataturbo.net/attachmen...ine=1396414512

Ha ha a vacuum pump would be ideal, maybe a little too much fab involved for my tastes.

Hell, if I was going that far I would do a dry sump oil system. Anyone have a few thousand $$$ to contribute towards my build? :D

Keith

I have my Pcv port welded shut. Then I went -10 hose off my breather port to a slash cut at the end of my DP with a check valve. That it. Simple and effective.

FTFY.

Assuming the second vent is still in the factory location (post filter, pre-TB, or better yet pre turbo) then isn't there vacuum present when you are under boost from a venturi effect?

Brain has the dumb again.

The op's pcv setups are perfectly adequate for N/A cars and milde turbo setups. We really only run into problems with crank case venting in 1 case. Big power turbo cars making significant lateral grip. For cars like this we delete the pcv port on the head because if we leave it open it just dumps oil out on sustained corners. See my car or Bundy's for some of the most advanced crank case venting on the site. I no longer have a pcv valve because my car doesnt see significant time cruising, if it did I'd run one. I have a massive AN fitting on the head, with the small port in the head baffling drilled out And I tapped the block for a 1/2" NPT fitting just above the starter to run another -10 an line. Both go to my air/oil separator and into my pre-turbo intake with a slashcut. At worst the slashcut doesnt work in the intake and I still get the slight vacuum created between the turbo and the air filter. I just didnt feel like doing the exhaust slashcut at this time, and its also illegal for every raceclass above mine for some stupid reason.

You pretty much dont want to just vent both sides of the engine to air without pulling any vacuum unless you're incredibly lazy.

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fuck your vacuum. you think mazda was engineering vacuum in the crankcase when they put a restrcitor on the breather line to the intake? past the small tiny little opening for all the baffling? if anything that will create positive pressure.

go fuck your goat.

Quality Control Bot Activated.

:laugh:

If you are running long hard left hand corners without a pcv in a big hp turbo car you well be losing oil out the pcv port in the head and probably on even less hp cars as there is alot of oil on the top of the head when running high sustained revs on the track. I am running big hp with the pcv in the system then to a catch/seperator can. As mentioned above under boost the pcv should be closed. The other side goes also to a catch can with a filter for when under boost it should be the only one working. Been that way for two seasons and seems to work just fine. Also if you are running a catch can with a filter on it you shouldn't have vacuam anywhere in the system should ya?

resurrection bump to see if I can get a consensus. Obviously different people have found different solutions that work for them but I want to make sure my plan will work for DE's.

The previous owner had the pcv connected to a diy catchcan that he mounted in the passenger wheel well and the breather hose on the driver's side was about 2 inches long with a small air filter on the end. As I discovered at VIR this weekend, that setup results in oil getting sprayed out of the filter and all over the engine bay. :facepalm:

I then bought some 6AN hose and tried to tee into the pcv hose leading to the catchcan. Fail. The catch can filled up real quick (just doing pulls off track) and the exhaust will spit out a nice big oil smoke screen on full boost and off throttle.

So I now have the pcv hose back to the original catch can configuration and the passenger side is now hosed to a temporary catch can that I had to seal quite well as it still blew oil out easily. At least it doesn't smoke heavily now! :D

So should I just build a proper catchcan on the driver's side and be done with it? Or would it be better to weld the port shut and increase the driver's side connection to a 10-AN? I don't like how much oil the driver's side breather port spits out and since it doesn't do it on the street I'm guessing it is just because of cornering forces.

you need better oil control rings on your pistons...

except I get no oil in either catch can under full boost in a straight line. And I get hardly any oil in the passenger side catch-can on track

and even if my rings are in fact bad (good possibility) isn't the driver's side breather vent leaking oil a known issue on track miatas?

Search is good
 

Since searching solves everything...:party:

So clean and sealing the driver's side baffles, welding the passenger side PCV and welding in a -10AN bung to the driver's side to route to a catch can is my next project.

My setup is 1 hose from each side of the valve cover going to the can that has a filter on the top. Am I doing it wrong? The can isn't plumbed with a 3rd line for a return. It can also be a sealed can without a filter. It's not getting anything but some moisture and left-over assembly lube. Should I cut a 3rd port in the bottom of the can and lead it to my pre-turbo intake pipe?

https://www.miataturbo.net/attachmen...ine=1399920653

At the track, the engine ran really rough and filled the catch-can quickly when I had the breather vent hose tee'd into the pcv line. Like Brain said, might be due to excessive blow-by or whatever but I never had a problem with the setup (not tee'd) until I got on track

I also noticed when the car is warming up for the first few minutes, if I blip the throttle I get some kind of steam (similar to what comes out of exhaust on a cool morning) that comes out of the filter on top. I'm thinking I should take the filter off and use that third port to run to right before the turbo..

Running those two hoses to the catchcan is a simple passive system though you may want to stuff it with steel-wool to help scrub the air of nasty oil vapors before it is vented through the filter.

You DON'T want to plumb a 3rd line from the bottom of the can because then all of the acidic crap that pools at the bottom of the can would get drawn into the intake. Kinda defeats the purpose of a catch can. Replacing the filter with a hose to the intake pre-turbo would be an active system and would be more environmentally friendly but would increase the chance of detonation.

Installing baffles or some steel-wool in the catch can to stop the air from just going straight out of the filter might fix any 'steam' coming out of the filter. With how that catch can is designed, I don't see it being all that effective at catching anything

I'm not worried about appeasing the EPA but am worried that I have the wrong setup for my purposes. I do about 4000 street miles a year. The setup I have I see on track cars that likely do less.

I just want to know what side effects to expect from running the system I am and if there's anything I can do to improve it.

Venting through a catch can to the atmosphere like that will give you no side effects. That is essentially what my car has been running for the last 5+ years

You're overthinking it. That setup is fine, and certainly way better than the crap that came stock on your car.

Maybe I take people here too seriously, but then what does this mean "You pretty much dont want to just vent both sides of the engine to air without pulling any vacuum unless you're incredibly lazy."

First off, i don't know what that means, because you're venting a valve cover, not two sides of an engine. Sounds like something Leafy would say. :rofl:

They're saying that a catch can/crankcase ventilation is most effective when you have some sort of vacuum pulling on your ports.

And on paper, that's true.

In the real world, if you can deal with some of the smells you might get from venting to atmosphere and your motor is healthy, what you've done works just fine and is found on 99% of modified motors making far more power under far more boost than anyone who has posted in this thread.

I can deal with the smells, girlfriend can't, but she doesn't really like riding in it anyway. I keep telling her the faster I go the less you can smell but :hustler:

When you open the oil cap does yours smell like fuel a bit? I can't go smell mine now cause I'm sick but just wondering.

I've never had a car that didn't have at least a slight smell of fuel in the oil after some miles.

If it REEKS of fuel and your oil is watery as hell from fuel, then you have a problem.

I wouldn't say it's watery.

Will this make my BP4W tick? :rofl:

Possibru! Really the oil acts as a bearing, so if it's not there, you've got nothing to take up the lash.


And yes, i know that was a joke. :rofl:

If I wanted to NOT vent to air, would the following be a big deal?

https://www.miataturbo.net/attachmen...1&d=1418850744

Has anyone tried using something like a "slash cut" in the intake tract to create some amount of vacuum? (not enough to act like a pump, but enough to draw the vapors out and burn them up?)

yes I have. Info should be in my build thread.

Chiburbian has the best diagram so far.


One BIG thing I see missing in all of this discussion is the physical location of any catch-can away from heat as far as possible i.e. behind the headlight or up in the cowl area on the other side of the divider. This is because the cooler the environment, the more condensing it will be doing and less vapors making their way back into the intake/vacuum source. You also don't want to have the can running VTA- always keep a closed-loop system.

Having vacuum on the crankcase also makes a lot of seals very happy.

I've researched this for the last few months and here is what I've come up with. My car is only mildly boosted so all I need is a mild solution. I do not want to vent to atmosphere because I hug trees.

1) I installed a heavy duty check valve coming out of the intake manifold, which normally goes to PCV valve. This is because even my GTX valve leaked boost into the crankcase. Now under boost there is zero issues with boost getting in the crank case.

2) Added a separator/can in between the check valve above and the PCV valve. Because even a stock engine will suck plenty of oil though PCV into the intake. At least now I can catch most of it and drain it.

That sums it up for PCV side of things. Since under boost that side of things does nothing for for venting CC under boost I moved to inlet side of things (well in an naturally aspirated engine). Which becomes the only outlet under boost. I figured this side of things needed some attention because it was never designed in our NA engines to be the only vent for CC.

3) Removed the valve cover and the plates on the underside sealing the PCV and "inlet" chambers in the VC. I only resealed the PCV plate for good measure. On the "inlet" side I opened up the small ~1/4" hole between the center chamber and the passenger side "inlet" chamber to 3/8", just like others have done on this board.
The purpose here is to allow more flow since it will be doing all the venting under boost.

I also realized that if any oil got from the center chamber to the "inlet" chamber it could not get back into the center chamber to drain because the hole does not go to the floor of the "inlet" chamber.

4) So I ground out the 3/8" hole toward the chamber floor a bit to allow the oil to drain out of the "inlet" chamber back to the center chamber sooner. I couldn't make the hole touch the floor of the "inlet" chamber because is would mean the plate would no longer seal. So now the oil will only have to be ~1/8" high in the "inlet" chamber before it can drain out. Not ideal, but better than before.

5) Pulled the stock 3/8" "inlet" nipple from the VC. Drilled and taped for a 3/8" NPT to 1/2" hose barb fitting. Again, just opening things up for flow when in boost.

6) Because I really want to keep the oil from getting from the center chamber to the "inlet" chamber, I put cooper wool in the center chamber around the drain area. Not a lot. Just enough so that all blowby must pass though it to enter the "inlet" chamber. I kept the wool away from the 3/8" transfer hole because I don't want any condensed oil being sucked into the "inlet" chamber. Next I resealed the plates to the valve cover.

Opening up those ports on the "inlet" side should significantly improve flow of blowby during boost.

7) Installed a second catch can/separator between the new 1/2" hose barb on the VC and the pre-turbo (or supercharger) "inlet" hose. This can catches any oil that makes it out of the "inlet" chamber in the valve cover.

8) Lastly I wrinkle painted the valve cover black. Because everyone knows this is best for a well constructed PCV system.

Overly complicated because I hug trees? Maybe. Does everything the stock system does only better? Yes.

lol if you are still using the passenger side valve cover vent to do anything.

Ok, so ideally you modify valve cover to pull twice out of drivers side?

Aside from that, any complaints?

hello.

https://www.miataturbo.net/attachmen...1&d=1418908179

^^ LOL

That's exactly what I have now and I had oil coating the inside of my intake and pooling in my turbo. I'm not sure how much, but when the guy who is doing my charge piping took it apart to do some fitting that's what he said and I don't doubt it.

You need a better catch can, and some copper scrubbies in your valve cover.

In Brain's illustration and my current set up, I don't need a better catch can, I need a catch can period.

I'll work on the scrubbies.

My main point was wither or not it was acceptable to plumb the "breather" line into the intake path rather than have a standard "filter".

Thats how mine is, and I havent had a drop of oil in the intake tube or turbo since I stopped trying to use the block vent I drill and put the copper scrubbies in the valve cover. And by not a drop I mean after i cleaned the tube out brake klean from getting drenched by the messed up setup the intake hasnt even formed an oily film on the walls like you'd expect. Thats with a -10an fitting on the valve cover and a -12 on the intake tube.

Cool Jonathan, thanks. I started reading your build thread yesterday but ran out of time before you "finished" the catch can part.

Picture, please. I looked at build thread, so saw the copper wool in the cover, but I'm not sure how the ports are routed.

Yes and if a majority could come to a resolution on this matter so I have a guide for my catch can setup before the turbo setup gets installed, I would be mighty appreciative. ;)

Just vent both sides of valve cover through either one baffled can vta or vent valve cover in to sealed baffled can with the can exit going into the intake of the turbo. I like option 1 but if it has to be sealed option 2 sounds ok to me.

Intake slashcut, looking at it from the air filter side, and after taking this picture I realized it got spun 180 from the direction it should have been... ooops.

Attachment 238561

Routing

Attachment 238562

Attachment 238563

You probably saw the inner design of the catch can itself in my build thread and I dont feel like searching back to re-post that stuff. I need to come up with a more elegant drain design though. Right now it drains from the catch can goes into a crystal geiser water bottle taped to the swaybar.