So I think a lot of my smoking after high revs is due to old rings and a lot of blow-by going back into the intake. I was looking at the thread about installing a catch can, but for some reason I can't view it right. So anyways I have a couple of questions for you guys.

The last picture of how to set one up looks like the best idea to me (where the intake and exhaust valve covers go to the catch can separately), but why does it keep from over pressurizing the intake side valve cover if they both go to the catch can (over having them tee'd together)? And how functional is it to not have a vacuum source to it (like routing it to the pcv valve on the intake after the catch can)?

Also I've been having trouble finding one with two inlets and one outlet. Or are any of the other options better than this idea? And is there any material in the catch can to help separate the oil from the air?

I would like to keep from routing it back to the intake (unless you guys think it more functional) and making a hard suction pipe with no nipples off it, except maybe one for a recirculating BOV in the future. (my car also has trouble idling at time because the pcv hose going to the intake isn't sealing well and is sucking in unmetered air, plus like I said, it's burning a lot of oil when coming down from high revs I think due to the PCV system)

Thanks guys

the best thing to do is to install the catch can to the hose that normally attaches to the suction pipe... under boost, the boost pressure will shut off the PCV valve and any blow by will get pushed out through the breather side into the suction pipe... if there's enough negative pressure in the suction pipe, it could even pull any blowby through that breather hose too

another thing you can also do is run a motor flush.... either autorx over a few thousand miles and a couple of gentle rinses, or the quick way, which is a 10-15 minute rinse at idle using something strong such as BG Quick Clean (look on ebay)... what it will do is clean out the piston rings and free them back out in order to make them contact the cylinder walls better (this reduces blowby and therefore less oil consumption)... I recommend that after running this stuff to put some crap oil in there and run it for another 5 minutes before changing the oil a second time to put in the good stuff... reason being is, there will be the residual cleaning agent inside and that stuff is evil to oil.... might as well try to get rid of any of it as much as possible!

I was trying to keep from connecting it back to the intake unless it's just that much better than putting a breather filter on the catch can.

so basically like this?



is there much blow-by from the intake side? and why does the exhaust side create positive pressure under boost, but not the intake side?

your diagram is correct
you need to stop thinking about "intake side" and "exhaust side" because that doesn't really matter in the scope of things... on other engines, you have a one piece valve cover instead of the split setup like the CAs and RBs do, but the fact remains that the principles and operations of the PCV system remains the same on any engine

under cruise, you are under vacuum, the breather hose (which is actually self explanatory), provides fresh air charge into the crank case (which in this case is a hose connecting the exhaust valve cover to the suction pipe) in order to displace any negative pressure built up inside of it... this is because the PCV valve is open due to the intake's vacuum state and any crankcase vapors are being drawn out from the intake valve cover in through the PCV valve and into the intake... as I said before, under boost, the boost pressure will push the PCV valve shut and nothing can go in or out that hose connecting the intake valve cover to the PCV valve.... any blowby is worked past the pistons and into the crankcase... all blowby then must escape through the breather hose (the exhaust valve cover side) and into the suction pipe.... obviously oil vapors and other crap will get sucked in through the suction pipe, which is why a catch can must be put in its place...

some people delete the breather hose altogether and install a filter directly on the valve cover instead... this kind of works in reducing on-boost blowby, but it won't reduce crank case pressure (which when high levels are reached, it can blow out seals), and you also run the risk of making a big mess under the hood... this is why japanese tuners install catch cans instead of breather filters... it allows the PCV system to still operate normally but catch any of the vapors instead, but most importantly, stay emissions legal... keep in mind a catch can works best if it has baffles/oil separators inside of it... if it's just a can with 2 nipples on it, it's pretty useless

now back to what I said about "intake side" and "exhaust side"... in other engines, such as the SR, Mazda BP, Toyota 4AG, etc, you have a one piece valve cover... there are two hose connections on the valve cover setup in a similar fashion like the CA one... if you just picture for a moment that your CA has a one piece valve cover, you'll understand what I mean... the two connections are internally separated under the valve cover... the breather side will lead to a gallery in the head that connects straight down to the crank case; completely isolated from the valvetrain... it will NEVER meet any air directly from the head... the PCV side ("intake side" as what you described your CA), will have a pickup at the bottom of the valve cover and will collect vapors from directly over the head... it will go into a series of baffles (how well it's designed depends on the engine) before it gets to the nipple you see on the top of the valve cover, and obviously from there you have a hose connecting it to the PCV valve (which can be located either on the valve cover itself or the intake... doesn't really matter)... the CA also has the baffles, which is why you see the giant rectangular "lumps" on top of each of the valve covers where the nipples are

What you said about imagining it had a single valve cover is what I had originally thought, but when looking at the diagrams I saw boost arrows for the exhaust side but not the intake side and was confused as to why. Thanks for clearing that up.

So would there be any problem with teeing the two valve covers together and making them both go to a catch can then to the suction pipe and scraping the PCV valve? The suction pipe will always be under some sort of negative pressure (not near as much as the manifold when cruising though), or would evacuation be better to have them set up like in the diagram? Or possibly teeing them to both go to the catch can then splitting the outlet to go to the PCV valve and the suction pipe?

And one more question. Would there be any adverse affects of having a recirculating BOV since it will force air into the suction pipe?

mdb4879 wrote:What you said about imagining it had a single valve cover is what I had originally thought, but when looking at the diagrams I saw boost arrows for the exhaust side but not the intake side and was confused as to why. Thanks for clearing that up.

So would there be any problem with teeing the two valve covers together and making them both go to a catch can then to the suction pipe and scraping the PCV valve? The suction pipe will always be under some sort of negative pressure (not near as much as the manifold when cruising though), or would evacuation be better to have them set up like in the diagram? Or possibly teeing them to both go to the catch can then splitting the outlet to go to the PCV valve and the suction pipe?

that defeats the purpose of a crankcase ventilation system and it won't be very effective removing crankcase pressure

And one more question. Would there be any adverse affects of having a recirculating BOV since it will force air into the suction pipe?

no, because the turbo always spins (it's not a supercharger), and air will always get pulled into the turbo and forced through the intercooler and into the cold pipe, no matter what

Sorry if I sound like I'm being ignorant, but if I tee'd the outlets from the valve covers together (since there are motors with just one valve cover) then have that go to the catch can then have the outlet from the can split into two (one to the PCV valve and one to the suction pipe) shouldn't that be just as effective at relieving crankcase pressure? When cruising the motor would create vacuum and pull the air from the can into the intake and the suction pipe should also pull a little bit, then under boost the valve would close and all of it would be forced to the suction pipe, right?

no because the exhaust side valve cover is for the fresh air breather, whereas the intake side is where the vapors are meant to come out
you can't tie them together because that will screw up all the plumbing

if you want to catch both sides, you need two catch cans

And I would guess the exhaust side makes most of the blow-by because under load the valve is closed, as you said, and it's forced out of the exhaust side, so the intake side isn't as important as far as the amount of vapors coming out. I'll just set it up like the diagram then.

Thanks for the help

Ok, so now I would like to know what causes the oil to separate inside the catch can. Is there any material inside of them? It looked like a few of them I found that actually showed a cut-away just had the inlet with a tube going to the bottom (I guess to make sure they get all the way there) and it's just open to the top. I'm kinda skeptical about this because I know water and oil separators for air compressors have some sort of vapor absorbing material (like desiccant or some type of foam or paper). So how well do these catch cans actually work?

And now that I think of it, I know it'd look kinda rigged, but what do you guys think of using an oil separator with a drain for an air compressor?

it's supposed to condense back to liquid inside the catch can using the tube mentioned... a better way is with baffles that will separate the oil

but you got the right mindset about what will work and what won't.... as far as the whole issue is concerned, liquid is liquid and vapor is vapor, the same concept applies from other applications for vapor from gas separation

Hi I realise this is an old thread. But I have a euro ca18det an both sides are joined together. I'm going to install a catch can like the diagram above, so should I separate both sides? Even though the euro ca18dets come like this?

Well I was going to link you to the stickied threads in the FAQ section, but I realize now that most of the image links are dead or just plain gone. I'm not sure what happened there. I guess we need to start a new thread about it and re-link it.

The long and short of it is that it's been decided that the best way to handle the catch can situation on our motors is to have 2 catch cans. One between the intake valve cover and the PCV valve, and one between the exhaust valve cover and the inlet pipe for the turbo. The issue is this; the intake side only really flows when on engine braking (manifold is under a vacuum), but it pulls A LOT when it does. When you're in boost, the PCV valve closes and it does nothing. The other issue is that on the exhaust side, the air flows both ways through that hose. When under manifold vacuum, filtered air is pulled from the turbo inlet, into the valve covers, through the heads, and eventually makes it into the intake, after picking up lots of oily air and crankcase fumes. When in boost, the air moves the opposite direction. Lots of crankcase fumes are being brought up through the tube that goes under the intake and behind the manifold and connects to the back of the intake side valve cover. Then those fumes travel up the intake side of the motor, across the head to the exhaust side, back down to the back of the motor, and then out the exhaust valve cover and into the inlet for the turbo. Confusing, right?