Well I made my choice I put it back on where it was originally - 80% of all that shite is unburned petrol so why don't just burn it again???
PCV Valve / Rocker Cover Breather
- Thread starter Aidan@EP-styling
- Start date
Well I made my choice I put it back on where it was originally - 80% of all that shite is unburned petrol so why don't just burn it again???
Glanza Gaz
Member +
Confused? read here for full explanation!!
On the 4efte it seems you have two crankcase breathers:
1. the PCV valve which is a one way valve allowing air out of the crankcase whilst off boost and stopping charged air from entering the crankcase via the post turbo intake when under boost.
2. the standard breather,which as far as Im aware flows in both directions once removed from the recirc valve.
Both these breathers work together to form the PCV SYSTEM
So to answer the question "does the PCV valve let fresh air into the engine whilst displacing blow by gasses?" would technically be NO. But if you were to ask "does the PCV system (ie the two breathers working in conjunction with each other) let fresh air into the engine whilst displacing blow by gasses?" then the answer would be YES!
You see as the PCV valve expels gasses from the crankcase into the intake whilst the intake is in a vaccuum state (off boost), "fresh air" is brought into the crankcase via the secondary breather due to displacement (ie the intake is causing a vaccuum within the crankcase because whilst off boost the two are connected via the PCV valve), which in turn causes air to be sucked in through the secondary breather to try and equalise the resultant pressure drop).
Whilst under boost however, the PCV valve is closed due to pressurised air from the turbo/intake trying to enter the crankcase(remember the PCV valve is a one way valve). In this state the secondary valve takes over the job of venting the crankcase gasses, but due to the secondary valve not having a vaccuum source and the crankcase not having another fresh air supply all it can do is equalise the crankcase pressure with atmospheric pressure therefore not taking in fresh air.
When talking about catch cans, their job primarily is to eliminate (vent to atmosphere cans) or reduce (sealed system cans) the crankcase gasses from entering the intake and causing contamination and octane issues leading to detonation.
To completely eliminate the probability of crankcase gasses entering the intake.
To do this you have to install a vent to atmosphere catch can, the best example i've seen on this thread I think would be rory's as he has tried to replicate the vaccuum system for the PCV valve BUT there is one vital flaw to it; it has no means of a fresh air supply to the crank case, both breathers are acting as how I explained the secondary breather works whilst under boost. To correctly set it up, you only need the PCV valve side and the 'to atmosphere under the car' pipe connected to the catch can (all other holes to the catch can blocked off), the secondary breather then needs a filter (higher flow the better) and left to suck in from the atmosphere.
The disadvantage of this system though is that it is technically illegal and lacks any major vaccuum source. Therefore your relying on air flowing under the car to suck out air from the catch can 'exhaust' so that you have a unidirectional PCV system that draws in fresh air from the seconday breather. In an ideal situation you would connect the catch can exhaust to a small vaccuum pump to provide a constant powerful enough vaccuum to attain this. To improve the system without a vaccuum pump I would recommend experimenting with a venturi valve connected to the exhaust of the catch can that is fed via the airflow under the car, this would provide a much better vaccuum whilst at speed.
To reduce the amount of crankcase gasses entering the intake whilst staying legal and maintaining a more constant fresh air supply.
To do this all you need do is copy the previous design ie PCV valve connected to catch can 'intake' , catch can 'exhaust' connected to (ideally use another PCV inline to the intake if this doesn't cause too much flow restriction so catch can isnt pressurised during boost) post turbo intake (part of intake where PCV valve used to go) and then put a filter on the secondary breather (not sure of legality on turbo cars). This will make sure that while off boost the intake vaccuum will suck crankcase gasses out of the crankcase through the catch can (catching some of the shite) then back into the engine, whilst fresh air is brought through the secondary filter. Whilst under boost however, the PCV valves close (assuming you've used two), stopping pressurised air from the intake entering the catch can and crankcase, whilst the secondary breather filter is used as an exhaust to vent crankcase pressures should they exceed atmospheric pressure (this is where Im unsure of the legality of using a filter here on turbo cars as essentially it's dumping to atmosphere albeit through a filter whereas on an NA car this wouldnt happen). Disadvantages of this set up are obviously that even though you are indeed 'catching' some of the shite in the catch can, some is still innevitibly being dumped into your intake.
Hope this has helped clear things up for people, I would post up some diagrams to help explain but I cant be arsed drawing any at this hour lol. Please feel free to fire any questions at me and Ill endeavour to answer them should I see them.
Gaz
Right it seems there's a lot of confused people on here with a lot of conflicting views haha. I'll do my best to answer some of these questions raised etc from my understanding of the whole pcv/catch can systems.
On the 4efte it seems you have two crankcase breathers:
1. the PCV valve which is a one way valve allowing air out of the crankcase whilst off boost and stopping charged air from entering the crankcase via the post turbo intake when under boost.
2. the standard breather,which as far as Im aware flows in both directions once removed from the recirc valve.
Both these breathers work together to form the PCV SYSTEM
So to answer the question "does the PCV valve let fresh air into the engine whilst displacing blow by gasses?" would technically be NO. But if you were to ask "does the PCV system (ie the two breathers working in conjunction with each other) let fresh air into the engine whilst displacing blow by gasses?" then the answer would be YES!
You see as the PCV valve expels gasses from the crankcase into the intake whilst the intake is in a vaccuum state (off boost), "fresh air" is brought into the crankcase via the secondary breather due to displacement (ie the intake is causing a vaccuum within the crankcase because whilst off boost the two are connected via the PCV valve), which in turn causes air to be sucked in through the secondary breather to try and equalise the resultant pressure drop).
Whilst under boost however, the PCV valve is closed due to pressurised air from the turbo/intake trying to enter the crankcase(remember the PCV valve is a one way valve). In this state the secondary valve takes over the job of venting the crankcase gasses, but due to the secondary valve not having a vaccuum source and the crankcase not having another fresh air supply all it can do is equalise the crankcase pressure with atmospheric pressure therefore not taking in fresh air.
When talking about catch cans, their job primarily is to eliminate (vent to atmosphere cans) or reduce (sealed system cans) the crankcase gasses from entering the intake and causing contamination and octane issues leading to detonation.
To completely eliminate the probability of crankcase gasses entering the intake.
To do this you have to install a vent to atmosphere catch can, the best example i've seen on this thread I think would be rory's as he has tried to replicate the vaccuum system for the PCV valve BUT there is one vital flaw to it; it has no means of a fresh air supply to the crank case, both breathers are acting as how I explained the secondary breather works whilst under boost. To correctly set it up, you only need the PCV valve side and the 'to atmosphere under the car' pipe connected to the catch can (all other holes to the catch can blocked off), the secondary breather then needs a filter (higher flow the better) and left to suck in from the atmosphere.
The disadvantage of this system though is that it is technically illegal and lacks any major vaccuum source. Therefore your relying on air flowing under the car to suck out air from the catch can 'exhaust' so that you have a unidirectional PCV system that draws in fresh air from the seconday breather. In an ideal situation you would connect the catch can exhaust to a small vaccuum pump to provide a constant powerful enough vaccuum to attain this. To improve the system without a vaccuum pump I would recommend experimenting with a venturi valve connected to the exhaust of the catch can that is fed via the airflow under the car, this would provide a much better vaccuum whilst at speed.
To reduce the amount of crankcase gasses entering the intake whilst staying legal and maintaining a more constant fresh air supply.
To do this all you need do is copy the previous design ie PCV valve connected to catch can 'intake' , catch can 'exhaust' connected to (ideally use another PCV inline to the intake if this doesn't cause too much flow restriction so catch can isnt pressurised during boost) post turbo intake (part of intake where PCV valve used to go) and then put a filter on the secondary breather (not sure of legality on turbo cars). This will make sure that while off boost the intake vaccuum will suck crankcase gasses out of the crankcase through the catch can (catching some of the shite) then back into the engine, whilst fresh air is brought through the secondary filter. Whilst under boost however, the PCV valves close (assuming you've used two), stopping pressurised air from the intake entering the catch can and crankcase, whilst the secondary breather filter is used as an exhaust to vent crankcase pressures should they exceed atmospheric pressure (this is where Im unsure of the legality of using a filter here on turbo cars as essentially it's dumping to atmosphere albeit through a filter whereas on an NA car this wouldnt happen). Disadvantages of this set up are obviously that even though you are indeed 'catching' some of the shite in the catch can, some is still innevitibly being dumped into your intake.
Hope this has helped clear things up for people, I would post up some diagrams to help explain but I cant be arsed drawing any at this hour lol. Please feel free to fire any questions at me and Ill endeavour to answer them should I see them.
Gaz
Gaz - another thing - like I've done would be
1) The pcv valve - left as standard!
2) The breather goes to the Oil catch tank then the air filter on top of the oil catch tank
This way it would be 100% legal and would keep your air filter clean!
Also in my opinion if the pcv valve left as standard the suction would be much better than any other methods so it would actually help the engine - but having 2 PCV valves and the oil catch tank is a good idea as well!
1) The pcv valve - left as standard!
2) The breather goes to the Oil catch tank then the air filter on top of the oil catch tank
This way it would be 100% legal and would keep your air filter clean!
Also in my opinion if the pcv valve left as standard the suction would be much better than any other methods so it would actually help the engine - but having 2 PCV valves and the oil catch tank is a good idea as well!
Glanza Gaz
Member +
I wouldnt really recommend that method mate as your not 'catching' any of the blow by gasses before they go into the intake which is what a catch can is supposed to do! Also when your breather sucks in through the catch can which it'll be doing most the time whilst driving, its sucking in the gasses from the catch can, so the air being vented out the crank case via the pcv is not even being replaced by 'fresh air'. Also im not sure about the legality as crank gasses are still being vented to atmosphere via the catch can filter? I'd much rather just put a filter on the secondary rocker cover breather instead.
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I don't get it! What intake are you on about? I Left the PCV valve to intake manifold - standard - no connection with the oil catch tank!
And the breather [JUST the breather] goes in to the oil catch tank which has a filter on top - don't see why is it illegal - it's a breather! Putting just a filter won't do any good in my opinion - it will get blocked over time [should I say very quickly] and reduce the air flow.
williamocarroll1982
Member +
Very interesting read
Yeah and a lot of different opinions!
Glanza Gaz
Member +
by intake I mean the engine intake post turbo side. You not connecting the PCV valve to the catch tank is the very problem ie your not catching any of the contaminents before they go back into the intake because whilst in a vaccuum state, which is most of the time, air is being drawn out of the crankcase through the pcv back into the intake. Therefore to create an effective catch tank you must use it to filter out the contaminents going back into the engine via the PCV. During vaccuum which is again most of the time, fresh air is being drawn INTO the crankcase through the secondary breather (note 'secondary' as the pcv is also a breather, although it only lets air OUT of the crankcase), so by placing a catch tank there all your doing is drawing fresh air through it, partially contaminating that fresh air via the catch tank before it goes into the crank case. Venting the secondary breather to atmosphere in any way may be considered illegal because during boost conditions when the PCV valve is closed, if crankcase pressures exceed atmospheric pressure then they will be vented out of the secondary breather until the pressures are equalised, Although out of the systems I've covered yours is most legal haha. The law states that any crank case gasses expelled must be sent back through the intake, NOT vented to atmosphere. Although tbh i've never had a problem with getting an MOT whilst venting the secondary breather to atmosphere, this may however be due to lack of knowledge the MOTer has on turbo PCV systems as on an NA car this WOULD be legal as the breather would always 'INHALE' due to the constant vaccuum on the intake. The amount of time it takes to clog the filter on a simple filter system compared to that of a catch can filter would be insignificant Id imagine and isnt a huuuge issue anyway.
to help explain the different systems I've sketched some diagrams (bit simple I know
!)Atmospheric style PCV catch can:
Sealed style PCV catch can:
PaulJJ style catch can:
all diagrams drawn based on; off boost situations with re-circ valve removed as this is the most common scenario.
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Good explanation here -)
I figured as 80% of all that crap coming out of the PCV valve is unburned petrol - let it burn again -) as it was off the factory!
In my case just the Filter on top of a breather - get clogged in oil pretty quickly, so I put an oil catch tank just for that and in fact I do get some stuff in the oil catch tank -)
I figured as 80% of all that crap coming out of the PCV valve is unburned petrol - let it burn again -) as it was off the factory!
In my case just the Filter on top of a breather - get clogged in oil pretty quickly, so I put an oil catch tank just for that and in fact I do get some stuff in the oil catch tank -)
how did you set up your catch can mate? same as rory?
I think Rory has no PCV system at all. You have diagrams avobe. I left the PCV valve as standard!
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yeah saw it already. does your set up collect oil? coz i know somebody same set up as yours, no oil present in their catch can.
Ohh yeah -) I have some crap in the oil catch tank -) not much but I can see that it does the job. It smells like petrol/oil mix to me.
dark_knight
Member +
running a freshly built engine so oil in the can is a thing of the past to me..