i was questiong catch cans in the FI forum when i came to a realization.

im running a b18b1 1994... and as far as i remember, the breather outlet on the valve cover had a rubber line connecting to a mounted metal tube, which then ran to the intake pipeing just before the throttle body. Am i correct?

after replacing my intake pipe with an aftermarket one, i believe i reconnected that breather outlet directly to the inlet tube pre-welded on the intake. was that a mistake? am i letting in too much oil vapor and dirtying up the whole head assembly? i've seen alot of n/a g3's that have a little filter there instead. is that bad also?

im very concerned could someone please enlighten me. much appreciated.
big medek

 

I connected mine to the spot on my intake... but it's a '93. Still though, I think it just needs some kind of outlet. I know someone told me I could just buy some kind of breather valve for it, but to be honest, I'm not exactly sure what the function is. Bump for some more info.

 

<FONT COLOR="royalblue"> Helps release pressure @ high rpms. Filter is just kewl rice. Keep the hose. </FONT>

 

still.. as i understand it. there is an oil mixture with those gases that come out of the breather. i remember reading something about that helping the engine and gaskets stay sealed. but im under the assumption i would need to clean out the tb, IM, and injectors after some mileage because the oil leaving residue.

what do you guys think?

 

I don't know about that one... that's where the info goes over my head. I wouldn't mind hearing an answer though, bump again for info.

 

Normally, the PCV valve sucks oily air out of the crankcase, directly into the intake manifold. Then this breather tube lets fresh air into the crankcase to make up for what's sucked out.

At WOT there isn't much vacuum to suck out thru the PCV valve. Often, there's enough blowby that the flow reverses in the breather tube, pushing oily air into the intake tube. It still gets taken into the engine & burned... but it makes a little more of a mess. I never heard about that oil keeping the gaskets healthy, that sound a little strange.

That metal tube you remember is joined with a coolant tube, to keep it warm. That's so the oil stays more vaporized.

Taking off that breather tube & replacing it with a filter is functionally OK, but it's not legal. When the flow reverses, it releases oil vapors into the air.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">
Taking off that breather tube & replacing it with a filter is functionally OK, but it's not legal. When the flow reverses, it releases oil vapors into the air.
</TD></TR></TABLE>

Emmisions...we don't need no stinking emmisions.

 

I can't belive someone hasn't said this already, but you need to SEARCH a bit more. There are several good quality articles about Catch Cans and closed vs open PCV systems. If I remember correctly our cars are closed PCV systems, and when you just jam those stupid breathers on the valve cover you change the system. What you mentioned about: "that helping the engine and gaskets stay sealed" I have read similar write-ups talking about crank case pressure and leading to improper ring seal and blowby, etc....... Anyway, I can't pretend that I know/understand all the physics of it off the top of my head, but I am sure you can find all the info you need if you look.

One example: http://www.c-speedracing.com/h...n.php

 

thank you gentlemen on the replys. of course i will continue to research this matter.

and wraith, i have searched and read several differant articles on catch can info and the pcv system. and as a general rule of thumb, i always search first. never the less thank you for your insight.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Wraith_G2IC &raquo;</TD></TR><TR><TD CLASS="quote">I can't belive someone hasn't said this already, but you need to SEARCH a bit more. There are several good quality articles about Catch Cans and closed vs open PCV systems. </TD></TR></TABLE>

hehe, ive searched and read all about that stuff. Yet i still don't understand it. Hard to read and understand. Maybe im just retarded. Oh well, I guess il just go play with some blown pistons now. "Vrrrrrrrroooooooooom....boooommmmm....uh oh, blew up again"

 

please dont **** on my thread. being an adult means acting like one. respect others...

 

sorry if i offended you . However, i did a bit of researching on it as well since i didn't know the answer. I found out that if you don't care about the emmisions, it is best to not run it back through the intake. Less fresh air= not as much power. I couldn't find anything about specific power increases. However, if your wanting to run it back into your intake, the best way is to run an oil catch can. Most however, are unbaffled, and the best way is to baffle it yourself. Most people seem to use steel wool for baffle material. This will trap most of the oil, keeping it from recirculating back into the intake. Hope this helps you.

 

You need to think in pressure differentials when determining crankcase ventilation flow direction.

You also need to keep in mind that the PCV valve is a metering device that is most restricted at very strong vacuum and then fully closed when manifold pressure is very high. How high is very high? I dunno, but suffice it to say that any time you're boosting, the PCV valve will be shut off completely by the plunger.
Any time the plunger is anywhere in b/w the two extremes is when it flows the most crankcase vapor....probably during light to medium load cruising conditions where the manifold vacuum is good, but not real strong.

You need to have a lower pressure out for the crankcase under positive manifold pressure conditions, or you'll risk blowing out a crankcase seal or oil dipstick.

Having both the purge (intake tube) and blow (to manifold) ends of the system seeing boost creates stagnant flow in the crankcase....until it finds a way out itself, typically through the aforementioned seals or dipstick tube. A breather filter on the purge side allows the excessive crankcase pressure to escape.

For some of us tho, it's more about finding a way to vacuum-evacuate the crankcase rather than just bleeding off the excess.

As a last note, it's been widely accepted that oil vapors in the intake charge make the combustion process more susceptible to pre-ignition and detonation events. I would guess that it would be somewhat of a ala diesel combustion of sorts.

 

that was very informative. im new to the pcv system and crankcase vapors. and as you said it is widley accepted that oil vapors make an engine more succeptable to detonation etc. one thing i noticed is that cars running boost, and some squeezing nos tend to use the breather. i understand now why they would not wish to run it back into the intake charge. but what im confused on, is that you mentioned some people m,ake it an issue to have it vaccumed out instead of just allowing it to "vent" through the breather. is that what the catch can does? i know it responsible for decreasing oil vapors when baffled. does it help the vaccum at all? (i will continue to research still)

thanks for the good info guys.

 

A catch can alone won't do anything to create a vacuum in the crankcase. That's still a blow-out system, not draw-out.

You would have to run a dry sump oiling system or a vacuum pump to get any appreciable vacuum under a wide range of operating conditions. There are also a couple of other ways of doing it, like using exhaust stream velocity or the car's speed and Bernoulli effect to draw the vapors out.

A dry sump oiling system would be ideal, but most people can't agree with the cost and elimination of the AC to mount the scavenging pump. The same goes for the mechanical vacuum pump. You could use an electric pump (from a GM brake booster system), but they aren't designed to pump any fluid more viscous than air or anything that could precipitate out and clog the pump. There's also no way to control the volume of flow of the electric pump, so it would pull way too much at idle and then maybe not enough at full load and rpm. A mechanically, rpm-driven pump would be the best suited for that purpose.

 

wow... i never thought i would get so far w/ this thread.

one last question. im not boosted yet but plan to in the next couple of years. as of right now, my engine alone is unmodded except for my CAI. would removing the afformentioned tube, connecting the breather @ the valve cover to the intake charge. And having it replaced w/ a breather, be ultimatley healthyer to my engine. or do i need some sort of vaccum to help remove the vapors?

`and which way should i go about it when im boosting?

 

Factory turbos (Saab, anyway...) have that breather tube connected to the intake pipe upstream of the compressor. So it's got just the little bit of vacuum from the filter resistance.

Don't connect it downstream of the compressor, because that'll pressurize the crankcase.