Catch Cans? whats the deal

[DennisRB30]

I have also seen a pic of a RB25 where the left rockercover hose connected straight up to the PCV valve and I did not see a hose comming up from that location. I'm not sure if it is a variation or if it was changed. Does yours have it?

[browny]

ok, now this is why I am confused.

On my RB20 the standard PCV system appears to be slightly different:

Maybe I have it drawn wrong?

How would a catch can for this system be plumbed up?

[Steve]

Between the rocker cover and the turbo inlet pipe.

[DennisRB30]

Thant would work, but it would only filter fumes on heavy throttle, during light thottle fumes would enter the plenum (although its not a huge issue but why not prevent that too if you can, I'm sure it would prevent the sparkplugs fouling a bit.)

According to a pic of a redtop RB20 I have infront of me, the system is how you drew it but there is no hose connecting the 2 rocker cover pipe connections. For best results you would hook it up the same way as my drawing but the brown hose would connect to the right rocker cover and the blue hose would connect to left rocker cover.

[browny]

The silver tops definitely have the hose connecting the two covers.

So if I want to be fussy and filter the fumes entering the plenum is this correct:

OR should I remove the rocker cover connecting hose?

[DennisRB30]

Yep. That will work. It just doen't use active crankcase scavenging, but if your not worried it will be fine. It looks good.

[adam 32]

why not just block the PCV valve off completely using a blanking plug?

[DennisRB30]

I think you need to do some more reading.

[Steve]

Browny, if you do it that way, air will just follow the path of least resistance, so you wouldnt get clean air going through the rocker cover - not that I think its necesarry - so it would be easier to just block off the line to the plenum as adam32 suggests.

[Damo]

Sydneykid,

where in carpoint.com is this "know your rights" i cant seem to find it.

[Ash]

just say sure officer u can look under then bonnet, then fart around for 5 mins saying, i was told there is a latch to open it here somewhere!

[browny]

Steve, The OEM piping doesnt look like it draws fresh air in anyway

I want to keep this 100% legal so blocking off the PCV is not an option.

[Steve]

Air is drawn from the air intake pipe before the turbo.

From a legal point, if you block the line from the plenum to the rocker cover, it does not make the car illegal, as the fumes are still being plumbed (via catch can if you have it) back into the plenum through the air intake and not just being vented.

[browny]

The air drawn from the intake does not neccesarily make it into the main body of the rocker cover because the two breather connections are joined.

Also, i'm in the situation where I need my car engineered, AFAIK one of the stipulations is that all emissions equipment is retained.

[Steve]

OK, dont do it then.

But just to clear it up. The breathers are joined, but in the stock form, the line from the rocker cover to the plenum comes out of the side of the rocker cover, not from the connections on top of the rocker cover.

If you have a close look at the engine, it will become painfully obvious.

Just so you understand, PCV is positive CRANKCASE ventillation, there is a one way valve to stop air being forced from the plenum into the rocker cover, ie, prevent a boost leak, BUT it doesnt matter what path the gasses from the crank case take, as long as they go through the induction system and get burnt in the cylinders. This is only done, as previously mentioned, to appease emissions requirements.

[browny]

On an RB20 all the connections are on the top of the rocker covers

[DennisRB30]

Originally posted by Steve

Browny, if you do it that way, air will just follow the path of least resistance, so you wouldnt get clean air going through the rocker cover - not that I think its necesarry - so it would be easier to just block off the line to the plenum as adam32 suggests.

Do not block off the PVC valve. How many times do I have to say it. The way you brownie drew the pic is good. If you block it off, all fumes will go through the intercooler and turbo at all times as it is the ONLY path. There will always be some oil left in the gasses even after it has been filtered so it will block your intercooler over time. With the PCV system in place the filtered fumes will go straight into the plenum and not through the IC around 98% of the time. The filtered fumes will only go through the IC under heavy throttle with the valve in place. This has nothing to do with crankcase scavenging. It just makes logical sense and to dissagree would just be down right subborn.

The silver RB20 is one of a minority of engines that does not SUCK the fumes out of the rocker cover. This is done to reduce oil consumption in a highly stressed engine. The usual way of doing it sucks most of the oil fumes out before they can condense back into a liquid. If it were me I would revert it back to the normal system by removing the hose that connects the rocker covers together.

Just think about what would happen inside the crank case. There are oil fumes in there, and unless your rings make a 100% seal there will be raw fuel and combustion by products in there aswell. It only makes sense that when the oil fumes recondense, they will mix will all that other nasty crap and end up in your sump. Having the PCV system hooked up the way it was originaly designed sucks a lot of this crap out before it ends up mixing with the oil. I would rather have this crap sucked out before it contaminates the oil.

And for the 6th time. Even in the sliver RB20's case, THE PCV VALVE WILL DO NOTHING FOR EMMSIONS. Looks at Brownies pic and pretend the PCV valve was blocked off. The fumes would make there way out to the intake and get sucked back into the engine anyway. Hopefully we can all see how this would happen. Understanding that, you might ask why its there in the first place. That answer lies in my first paragraph! To stop 98% of the oil vapours going through the intercooler and dreamatically reducing its thermal effeciancy over time.

[DennisRB30]

Brownie, just do it the way you drew it. It looks at least you understand about the fumes through the IC thing. But if you would also like the benefits of active crankcase scavenging (how ever minute they might, or might not be) Hook it the way I showed. Theres a bit less plumbing too. You just need to find some decent one way valves.

Heres a modified version for a RB20.

[Steve]

Dennis, you are pretty paranoid about fumes going into the cooler. I dont know how you could say 98% of the time the fumes go directly into the plenum, unless your car is a lag monster and you rarely hit boost. I cannot drive my car with out going on boost, even driving sedately, just keeping up with traffic - if I am accellerating at over 2k rpm, she boosts. Perhaps you have a restictive exhaust system?

The amount of oil mixed with the crank case gasses is pretty minor when not on boost, if at all. This is why its only really necessary to fit a catch can when you wind the boost up, because otherwise there is insignificant amounts of oil going through the system - in a healthy engine anyways.

Do not block off the PCV valve. How many times do I have to say it.

you only have to say it once - its your opinion, my opinion differs. Perhaps if you could give examples of actual problems you have encountered it would add more weight to your statement. But at the end of the day I wont tell you what you have to think, dont try and tell me what I have to.

I listen, I evaluate, I compare statements to my own personal experience - and it takes alot more that a repeating a statement over and over, with out qualification to make me change my mind.

I am really sorry if this upsets you, as you do seem to be getting a little upset?

Agreed the pcv valve does nothing for emissions, I really dont know what your getting all upset about there. All I was getting at is that it is illegal to vent crankcase gasses to atmo. Agsin you seem to be getting a bit upset? Why?

[DennisRB30]

Na its cool man, im not upset or paranoid. 98% is just a bullshit figure I pulled out of my arse. But you can see that it is a large % of the time. It could even be more that 98% if the car is used mainly on the HWY. I'm just sick of saying the same shit over and over again. The thread was about PCV systems so I just added my opinion. The reason I raved for so long was that I felt my valid point had been ignored or missunderstood. I couldn't care if people dissagree with me as long as they have understood what my point was first, and tell my why their particular way is better (which no-one including you has done in this thread as of yet). I am not stubborly held in my ways, a simple explination of why any given method is better will change my mind.

I think you have finaly understood what I was trying to say, but seriousy... Why would you purposly want fumes to (potentialy) clog up the cooler when it is just as easy to have them go staight down the plemum? Given the fact that this whole thread is based around preventing blowby related probs, I would like to here what the benefits would be, by intentialy passing extra fumes through the intercooler for no apparent reason. I will be VERY interested to here you reply. It seems very 1 step forward and 2 steps back to me is all. I hate to see people spend money and time on mods that might have negative effects. All it takes is a walk down to the importer to see how much crap ends up in a second hand cooler, even on stock systems which vent to the plenum.

And also, now that you have accepted that the PCV does nothing for emmisions, would you please tell me what you think it is there for?

No hard feelings