Catch Cans? whats the deal

[DennisRB30]

Just spotted an error in the heading of my pic, is should read "it will not let ANY vapours get sucked into the engine under heavy throttle" Which in the only time that it realy matters.

[Steve]

Where does the clean air come from? PCV is to remove the blow by from the crank case, so it only takes the air (burnt gases from the pistons) out of the crank case that shouldnt be there, not put fresh air in there.

As I explained in previous posts, before emissions laws, PCV just went to the rocker cover and then to atmo throught the oil filler cap, at no stage was the vacuum in the plenum used to clear the gasses, but it did have a one way valve so that air could flow from the crank case to the rocker cover only - thus I believe where the word positive comes from in PCV.

Recirulating these gasses can in no way actually be good for combustion or perfromance, I am sure that companies these days wouldnt plumb these potenially harmful (to the turbo/intercooler/combustion process) back unless only to appease the greenies/govt of this world.

The idea of putting all these gases through some sort of filtration before returning it for combustion, has merit IMHO.

[DennisRB30]

The PCV valve is after the TB, where there is strong vacuum, the gasses will be SUCKED out and fresh air will be sucked in from those 2 hoses on the rocker cover after it has been filtered and metered by the AFM. You could do away with the PCV valve and direct the hoses into the intake and all the fumes would be burnt in the engine anyway.

Yes, recuculating the gas is not good for performace, but it is good for emmissions. That is why it is done (like I said you dont need a PCV system to get the gasses back into the engine).

When you accelerate the manifald vacuum decresses and the PCV valve closes, the gasses then get PUSHED through the rocker cover hoses and go in to the intake, fesh air replaces the fumes.

My system works like stock under closed PCV valve conditions (plus filtering) , but when you put your foot down no crap is sucked back into the engine. So it only sucks in fumes under light throttle when fumes won't make your car ping and the power loss from burning blowby is not an issue. You still get the benefit of positive crankcase ventilation and the benefit of not sucking crap when you are accelerating hard.

[armbrusb]

At one point I had both lines from my catch can attached to each of the rocker covers. The covers were joined by the U-shaped hose. The catch can was the attached to the intake before the turbo. I blocked the intake plenum.

I'm not sure if there two are related, but I have blown out some of the silastic between the block and the sump - oil leaks now.

Was blocking the plenum and leaving the fumes to find their own way to the can the cause of this?

[Steve]

I see what you mean about the fresh air, but really I dont think it helps the crank case, probably just helps thin the fumes when they enter the plenum.

Postitive Crankcase Ventilation does not require vacuum from the plenum, nor fresh air from the intake - it is purely the removal of the gases from the crankcase. They go out all on their own due to the pressure of more gas entering the crankcase every time a cylinder fires.

If you want a system that works like stock with filtration under boost, and stock type recirculation whilst at light throttle - just fit a catch can - thats what they do.

I just dont understand the point you are making, it sounds to me like you are trying to re-invent the wheel:)

[armbrusb]

I just want to remove the ugly hose going from by rocker cover to my plenum and want someone to say it's ok.

[DennisRB30]

Man, why do you think they put a valve behind the TB where there is vacuum? Like I said for the 5th time, you don't need a PCV system to get rid of the gas. The gas will push its way out of the hoses on the rocker cover and enter the engine that way without the PCV system in place.

Understand?

[armbrusb]

Sweet.

[browny]

DennisRB30 - where on the engine does the brown hose come from in your pic?

[JimX]

Here is a picture of my current oil catch can. As you can see, I wouldn't mind improving it somewhat

[Steve]

Dude, nothing wrong with that, asl long as the coppers dont see it you'll be right.

[JimX]

Well, that's the problem. If they pop the bonnet, that's the first thing they're gonna see. If I can have an unobtrusive can somewhere not immediately visible, it would be a load off my mind.

[Steve]

Just get some hose, and pop it out of the way somewhere. It is suposed to join the inlet, so if it just disappears you might be safe.

[turbomad]

It doesn't matter if the can is visible as long as it plumbs back to the intake and not to atmo. Basically you just want to filter the blowby before it get's sucked up into the engine again, that's why the debate over blocking the PCV valve, with it in place whenever your not in boost the gases will enter the plenum directly, no filtration. I havn't blocked my PCV valve yet and my catch can is totally clean suggesting that most of the blowby is actually sucked out when not in boost, almost defeats actually having one.

[JimX]

Turbomad, I know that it doesn't matter if the can is visible if it's legal, but if it only has one inlet and no outlet other than the breather, I don't want it to be visible.

Steve, moving the existing breather was something else I contemplated, but I thought I'd rather have something to catch the oil rather than spread it evenly around the interior of my engine bay. Although, I've done around 15000km with that setup and I've never cleaned the engine bay and it doesn't look too filthy, so maybe I don't need the can just yet.

[DennisRB30]

turbomad, does yours plumb back?

What is happening is that the PCV system is still doing its job of sucking air through the crankcase.

****************************************************

Under most conditions air goes IN through the 2 rocker cover hoses not out.

****************************************************

The PCV system SUCKS air through the 2 hoses on light throttle, that is why your catch can is clean. The only time that gas comes out of these 2 hoses is when you boot it. THIS IS A GOOD THING as most of the time crap does not go through all the inlet piping turbo and cooler. (do an experiment, disconnect the the pipe that goes to the intake and put your finger over it you will see for yourself that it sucks and does not blow) The gasses will not have any meaningfull adverse effects to the engine under light throttle. They will just be burned up. We all want performance right? Then the aim is to stop any crap going in the engine under heavy throttle when it actually matters, and to stop residue clogging the intercooler etc.

When you boot it the PCV valve will close and the blowby will then PUSH its way through the other 2 hoses, if you have a plumb back the fumes will be filtered by the can before they go back into the intake. If you have an atmo the fumes will escape into the air. So what matters is most is being achived, ie no crap going into the engine under heavy throttle. Under light throttle the fumes will go into the plenum unfiltered (which does not realy matter anyway as its only on light throttle, and no fumes go through the inlet trackt and intercooler etc)

In most of the plumb back systems meantioned in this thread, closing off the PCV valve defeats the overall purpose of fitting a catch can in the first place. Sure, when you do it your catch can will actually do something under light throttle and not just heavy throttle, BUT... All the fumes will be forced to travel along the whole intake track AT ALL TIMES not just heavy throttle. The fumes will go through all the pipes, turbo and cooler all the time, you might want to kid yourself that there is no oil left in the gas after the catch can but there will always be some crap left in it. It WILL build up in the cooler over time.

Is it starting to make sense yet?

I'm not even going to get into the possble idle probs and vaccum leaks some of the mentioned systems can cause.

The system I drew up takes all of this into accout (when done in plumb back style, see attached text). Under light throttle the air is sucked through the 2 pipes and crank case, goes through the catch can and in to the plenum and not through the intercooler and turbo!! Most of the systems discribed in this thead don't filter the gas under light throttle when it is being sucked through the PCV valve but mine does. Plus the system has the bonus of active crank case fume scavenging under light throttle (unlike the system of disconnecting the PCV valve where gasses must pass through the cooler and turbo at all times). If your are sceptical about the PVC stytems use (even though I debunked the misconsptions 5 times) you can think of it as an added bonus!! Under heavy throttle only, the filtered fumes will go back into the intake. It won't effect the idle because the PCV system still works like stock, only filtered. It also won't effect the idle when used it atmo mode because, there is no parralell path for unmetered air to go into the plenum, ie getting sucked in through the catch can filter. Also when the system is used in atmo mode, the only time gas escapes to the air is under heavy throttle, this will stop the filter clogging and is much better for the environment.

I'm just trying to make the point clear, so you can all decide what is the best, but for people to decide, they first have to understand what is happening. It just seems like a lot of you don't understand the opperation of standard and modified systems (not picking on anyone inparticular) My overall point is to try and explain how the various systems work so you you can decide the pros and cons of each for yourself. I am just trying to make people understand how my system works, as it seemed it was being dismissed without being understood first

Any questions?

[turbomad]

Yes I understand how it works, but some members made comments in another thread that the idea of having a catch can is to also block the PCV valve off as well, I'm contemplating whether or not to do it, that's all.

[DennisRB30]

Fair enough. As long as you realise what will happen when you block it off, and you are fine with the idea that you won't have positve crankcase ventilation and all the gasses will pass through your turbo and intercooler at all times, as oppesed to only under heavy throttle.

Sure they will be filtered, but whats better? (remembering that the can can't filter all the fumes)

(a) Having crank case gasses go through the whole intake tract, turbo and intercooler 100% of the time, with no positve crank case ventilation.

(B) Having crank case gasses go through the whole intake tract, turbo and intercooler maybe, say 2% of the time while still having the positive crank case ventilation (Hell, if you do it my way even the PCV gasses are filtered).

Its your call, I know what has the worse potentinal of clogging the intercooler over time. If you don't belive in the benefits of positve crank case ventilation to prevent corrosive reactions in the oil, just think of it as a way to drastically minimise the amount of fumes that can potentially clog the intercooler.

[browny]

DennisRB30:

Where is that brown hose coming from on the engine?

[DennisRB30]

Its where the stock PCV valve hooks up to.