Catch can advice
07 April 2015, 09:25 PM
#1
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Catch can advice
I know this may have been asked in the past..but I'm a little confused as to which way to go with it so any advice appriciated.
Friend of mine who's building an E46 330 race car recently installed a catchcan system and inspired me to carry it out on the P1 when I get it out from storage next week.
SO I've done alot of reading/youtube vids etc and understand fully the benefits of having it in place especially on out P1's running any mods etc..I've read a couple of helpful guides on here to install too.
I've also read that it's better to install 2 seperate catch cans for the crankcase ventilation system and the cam cover system rather than bridging/teeing the 2 into one..can someone advice on this?
Also read that the whole PCV works on vaccum pressure and that messing with it is not a good thing too??..how true is this?
Also have read you need some form of packing inside the can to actually catch the oily residue like steel wool etc?
So my question is how many of us are running catch cans and in what configuration?
Cheers
Friend of mine who's building an E46 330 race car recently installed a catchcan system and inspired me to carry it out on the P1 when I get it out from storage next week.
SO I've done alot of reading/youtube vids etc and understand fully the benefits of having it in place especially on out P1's running any mods etc..I've read a couple of helpful guides on here to install too.
I've also read that it's better to install 2 seperate catch cans for the crankcase ventilation system and the cam cover system rather than bridging/teeing the 2 into one..can someone advice on this?
Also read that the whole PCV works on vaccum pressure and that messing with it is not a good thing too??..how true is this?
Also have read you need some form of packing inside the can to actually catch the oily residue like steel wool etc?
So my question is how many of us are running catch cans and in what configuration?
Cheers
07 April 2015, 09:35 PM
#2
Has been covered many times on here,there is some good threads floating about on this subject. This one is a good read
https://www.scoobynet.com/general-te...od-advice.html
https://www.scoobynet.com/general-te...od-advice.html
07 April 2015, 09:40 PM
#3
Not gone through the link above but you don't have to have 2 catch cans or t piece the crank breathers, just buy a can with enough ports to fulfill your needs 
type-ellis on here makes and sells them. I bought and fitted one late last year on my car. I had broken a plastic oil pipe and unless I wanted to spend a small fortune a catch can was the best way to go
type-ellis on here makes and sells them. I bought and fitted one late last year on my car. I had broken a plastic oil pipe and unless I wanted to spend a small fortune a catch can was the best way to go
Last edited by EOEUMC; 07 April 2015 at 09:46 PM.
07 April 2015, 10:54 PM
#4
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Not gone through the link above but you don't have to have 2 catch cans or t piece the crank breathers, just buy a can with enough ports to fulfill your needs
type-ellis on here makes and sells them. I bought and fitted one late last year on my car. I had broken a plastic oil pipe and unless I wanted to spend a small fortune a catch can was the best way to go
type-ellis on here makes and sells them. I bought and fitted one late last year on my car. I had broken a plastic oil pipe and unless I wanted to spend a small fortune a catch can was the best way to go
07 April 2015, 11:45 PM
#5
The following is my opinion based on research, testing my own car and what I found on the net. It goes against many peoples advice of "just pipe everything to a can" but I honestly think most people just don't understand the system.
On the classic you have the breather system as follows:
There is a pipe which is connected to the intake hose near the power steering pump. The pipe splits into two and goes to each head.
You then have the crank breather located just to the right of the turbo and to the left of the throttle on the block. This is divided into two. There is a small opening which leads back to the intake hose just before the turbo. There is a bigger opening which is connected to the throttle body via a one way valve (PCV Valve).
On boost and full throttle the PCV is closed. The pressure in the crank case exits the engine via the hose into the intake hose pre-turbo. It may also vent a bit through the heads but not much.
When you are off boost and there is vacuum in the intake manifold the PCV opens and the vacuum pulls dirty air from the crank case vent into the intake manifold to burn it off in combustion. This causes a vacuum in the crank case and clean air is sucked into it via the two head vents. As the head vent pipes and the two way crank vent can vent are all connected to system post MAF it is all read equally (no air escapes after the MAF has accounted for it).
If you VTA then you lose the metered air.
If you VTA and don't seal the PCV you will suck unmetered air in.
If you VTA you lose the vacum of the PCV which means new clean air is not introduced into the engine and the old acidic air will increase wear.
I have just been heavily researching this area myself and there is massive confusion about this system on the net. A lot of people think the rocker breathers are literally to let out pressure into the intake. Their real function is to let fresh air be drawn into the heads and down into the crank case. In the tech manual it confirms this.
Apparently the oil in your crank case gets quite acidic as it is used and these acids are bad for the engine (a reason you change your oil every six months even if you only did 500 miles). So ideally you want them properly flushed out via the positive ventilation system that Subaru designed. By just letting them breath then the dirty air to some degree will stay in there. Another reason the positive system is good is apparently it assists ring seal... not sure on that one but a few people seem to think this.
Now many have simply vented it all to atmosphere and probably noted no problems. But personally, now I understand how it works and the reasons behind it I am going to stick to a modified version of the original design that still works in the same way. I am going to run the crank breather through a catch can but keep it within the same routing of pipework.
I know its all a mess but it seems unlikely that Subaru would go to so much trouble making such a complex system just for the hell of it. For those who say "it's just for emissions we don't need it". I think this is part of the reason but if it were just for emissions the system could just be passive and they wouldn't have bothered with the PCV valve, the carefully designed t piece which gives priority to the PCV route rather then to the turbo intake and other bits.
Finally I want to say catch cans are a good thing. But fitting one without binning the PCV system is a challenge. I am sticking with the multi million dollar car companies design over what people do because other car enthusiasts do it. But each to their own, it's your car.
Last edited by FMJ; 07 April 2015 at 11:47 PM.
07 April 2015, 11:56 PM
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It won't clear the crank case properly IMO. You have no fresh air moving through it.
The following is my opinion based on research, testing my own car and what I found on the net. It goes against many peoples advice of "just pipe everything to a can" but I honestly think most people just don't understand the system.
On the classic you have the breather system as follows:
There is a pipe which is connected to the intake hose near the power steering pump. The pipe splits into two and goes to each head.
You then have the crank breather located just to the right of the turbo and to the left of the throttle on the block. This is divided into two. There is a small opening which leads back to the intake hose just before the turbo. There is a bigger opening which is connected to the throttle body via a one way valve (PCV Valve).
On boost and full throttle the PCV is closed. The pressure in the crank case exits the engine via the hose into the intake hose pre-turbo. It may also vent a bit through the heads but not much.
When you are off boost and there is vacuum in the intake manifold the PCV opens and the vacuum pulls dirty air from the crank case vent into the intake manifold to burn it off in combustion. This causes a vacuum in the crank case and clean air is sucked into it via the two head vents. As the head vent pipes and the two way crank vent can vent are all connected to system post MAF it is all read equally (no air escapes after the MAF has accounted for it).
If you VTA then you lose the metered air.
If you VTA and don't seal the PCV you will suck unmetered air in.
If you VTA you lose the vacum of the PCV which means new clean air is not introduced into the engine and the old acidic air will increase wear.
I have just been heavily researching this area myself and there is massive confusion about this system on the net. A lot of people think the rocker breathers are literally to let out pressure into the intake. Their real function is to let fresh air be drawn into the heads and down into the crank case. In the tech manual it confirms this.
Apparently the oil in your crank case gets quite acidic as it is used and these acids are bad for the engine (a reason you change your oil every six months even if you only did 500 miles). So ideally you want them properly flushed out via the positive ventilation system that Subaru designed. By just letting them breath then the dirty air to some degree will stay in there. Another reason the positive system is good is apparently it assists ring seal... not sure on that one but a few people seem to think this.
Now many have simply vented it all to atmosphere and probably noted no problems. But personally, now I understand how it works and the reasons behind it I am going to stick to a modified version of the original design that still works in the same way. I am going to run the crank breather through a catch can but keep it within the same routing of pipework.
I know its all a mess but it seems unlikely that Subaru would go to so much trouble making such a complex system just for the hell of it. For those who say "it's just for emissions we don't need it". I think this is part of the reason but if it were just for emissions the system could just be passive and they wouldn't have bothered with the PCV valve, the carefully designed t piece which gives priority to the PCV route rather then to the turbo intake and other bits.
Finally I want to say catch cans are a good thing. But fitting one without binning the PCV system is a challenge. I am sticking with the multi million dollar car companies design over what people do because other car enthusiasts do it. But each to their own, it's your car.
The following is my opinion based on research, testing my own car and what I found on the net. It goes against many peoples advice of "just pipe everything to a can" but I honestly think most people just don't understand the system.
On the classic you have the breather system as follows:
There is a pipe which is connected to the intake hose near the power steering pump. The pipe splits into two and goes to each head.
You then have the crank breather located just to the right of the turbo and to the left of the throttle on the block. This is divided into two. There is a small opening which leads back to the intake hose just before the turbo. There is a bigger opening which is connected to the throttle body via a one way valve (PCV Valve).
On boost and full throttle the PCV is closed. The pressure in the crank case exits the engine via the hose into the intake hose pre-turbo. It may also vent a bit through the heads but not much.
When you are off boost and there is vacuum in the intake manifold the PCV opens and the vacuum pulls dirty air from the crank case vent into the intake manifold to burn it off in combustion. This causes a vacuum in the crank case and clean air is sucked into it via the two head vents. As the head vent pipes and the two way crank vent can vent are all connected to system post MAF it is all read equally (no air escapes after the MAF has accounted for it).
If you VTA then you lose the metered air.
If you VTA and don't seal the PCV you will suck unmetered air in.
If you VTA you lose the vacum of the PCV which means new clean air is not introduced into the engine and the old acidic air will increase wear.
I have just been heavily researching this area myself and there is massive confusion about this system on the net. A lot of people think the rocker breathers are literally to let out pressure into the intake. Their real function is to let fresh air be drawn into the heads and down into the crank case. In the tech manual it confirms this.
Apparently the oil in your crank case gets quite acidic as it is used and these acids are bad for the engine (a reason you change your oil every six months even if you only did 500 miles). So ideally you want them properly flushed out via the positive ventilation system that Subaru designed. By just letting them breath then the dirty air to some degree will stay in there. Another reason the positive system is good is apparently it assists ring seal... not sure on that one but a few people seem to think this.
Now many have simply vented it all to atmosphere and probably noted no problems. But personally, now I understand how it works and the reasons behind it I am going to stick to a modified version of the original design that still works in the same way. I am going to run the crank breather through a catch can but keep it within the same routing of pipework.
I know its all a mess but it seems unlikely that Subaru would go to so much trouble making such a complex system just for the hell of it. For those who say "it's just for emissions we don't need it". I think this is part of the reason but if it were just for emissions the system could just be passive and they wouldn't have bothered with the PCV valve, the carefully designed t piece which gives priority to the PCV route rather then to the turbo intake and other bits.
Finally I want to say catch cans are a good thing. But fitting one without binning the PCV system is a challenge. I am sticking with the multi million dollar car companies design over what people do because other car enthusiasts do it. But each to their own, it's your car.
It's for this reason I've not just bought a catch can and stuck it on without informing myself about how the system works..it makes no sense to me to modify something when you don't know how it actually works.
08 April 2015, 11:04 AM
#7
Now many have simply vented it all to atmosphere and probably noted no problems. But personally, now I understand how it works and the reasons behind it I am going to stick to a modified version of the original design that still works in the same way. I am going to run the crank breather through a catch can but keep it within the same routing of pipework.
i'm using the RCM oil catch tank (on a classic) atm, with the assumption that they would probably have a good working solution compared to buying the cheapest one from ebay.
wouldn't they have done a lot of research on this too?
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08 April 2015, 08:33 PM
#8
could you perhaps illustrate with pictures or drawings what you will connect to where? i have a hard time following (being a none native english speaker).
i'm using the RCM oil catch tank (on a classic) atm, with the assumption that they would probably have a good working solution compared to buying the cheapest one from ebay.
wouldn't they have done a lot of research on this too?
i'm using the RCM oil catch tank (on a classic) atm, with the assumption that they would probably have a good working solution compared to buying the cheapest one from ebay.
wouldn't they have done a lot of research on this too?
I may get around to a guide at some point but I work full time shift work, plus overtime. In my spare time I test ballistics, work on my track car and try to have a bit of a life so I don't have much free time.
The issue I am really talking about is the removal of the PCV system and not the fitting of a can. The can is good. But IMO the PCV system is worth keeping. Yes you can keep PCV and fit a can. But it's difficult as there isn't much room in the place you need to fit the can (between PCV three way valve on block and the PCV one way valve on the intake manifold).
So some questions. Why do a reputable company who know their stuff sell a catch can?
Simple. They work and they are popular. Again it's not the can fitting that's wrong here.
Yes the can works and will gather the oily air up which is not good for your engines performance. It's a proven concept and very popular in car moding because:
It's easy.
It visibly works.
The theory behind it is easy to understand and demonstrate.
It's cheap (well the cheap cans are, the decent ones are expensive for what they are).
Everyone does it! All the people on car forums, with track cars in magazines. They all do it.
Will fitting a catch can and removing the PCV cause my engine to be damaged? No. Almost certainly you are not going to cause any noticeable damage to your engine and it will live on and be killed by another issue (det, bearing failiure, poor maintenance, user error, age etc).
So why not just bin all that pipe work and fit a nice shiny catch can?
The PCV system works. It was designed because people at Subaru who designed the engine thought that the issue of having acidic dirty air in the block was enough of a problem that they didn't think just letting is vent was enough. They thought that a better system was to use the vacuum of the inlet to suck clean air through the heads through the block and out of the crank case vent ensuring that the block was kept fresh.
Now I cannot prove that this acidic air has an effect on the engines reliability. The only way to do this would be to set up many test engines all brand new and run half with PCV and half without for the equivalent life of the engine and then see which dies first and why.
But Subaru put it there for a reason.
However It's well proven that high power Imprezas run fine with catch cans so we know removing the PCV can't be that bad?
I do everything I can to keep my engine reliable. So why would I remove this system? That's my thoughts on it. Each to their own and many will stick with "But I want a shiny racing catch can because it looks cool and will stop dirty air going in my intake". Both valid arguments and I don't knock people for that.
Last edited by FMJ; 08 April 2015 at 08:35 PM.
08 April 2015, 08:59 PM
#9
FMJ,very well answered again(must feel like Groundhog Day sometimes tho lol)
The last thread,which wasn't that long ago on 'catch can advice' gave good advice And only a small search button away
Bludgod also put up a good link
http://forums.nasioc.com/forums/showthread.php?t=754710
#done to death
The last thread,which wasn't that long ago on 'catch can advice' gave good advice And only a small search button away
Bludgod also put up a good link
http://forums.nasioc.com/forums/showthread.php?t=754710
#done to death
09 April 2015, 03:35 PM
#10
I'm using an OBP three port baffled can on my V2 sti. I fitted it after finding oily residue in the throttle body and intercooler. I was also getting smoke from the exhaust on start up after a "spirited" drives 
Im using this can which is for a new age car but asked OBP to change the spigot sizes so the hoses fitted to the cam cover and block breather. 12mm OD for the cam cover vent and 16mm for the block vent.
Ive left the PCV in place unfiltered with no issues yet
Its solved my oil in the inlet issues, if I had any doubts about this being a worth while mod they disappeared the first time I came to empty the can. I also chose not to return to sump, Im glad this muck isnt going back into the oil
Im using this can which is for a new age car but asked OBP to change the spigot sizes so the hoses fitted to the cam cover and block breather. 12mm OD for the cam cover vent and 16mm for the block vent.
Ive left the PCV in place unfiltered with no issues yet
Its solved my oil in the inlet issues, if I had any doubts about this being a worth while mod they disappeared the first time I came to empty the can. I also chose not to return to sump, Im glad this muck isnt going back into the oil
09 April 2015, 03:46 PM
#11
Yep, we know catch cans work. And we know that the stuff they collect is better out then in.
Nobody is disputing that.
How have you plumbed it? When you say the pcv is in place unfiltered do you mean the pcv valve on the inlet is not connected to anything? Not blocked?
As Subaru designed the engine the crank one is the only outwards breather. The two cam ones are there to suck fresh air in. If you join them to the can they can only suck dirty sir back in but of course workout the Pcv there will be no suction. So they will instead work as poor outward breathers instead.
Nobody is disputing that.
How have you plumbed it? When you say the pcv is in place unfiltered do you mean the pcv valve on the inlet is not connected to anything? Not blocked?
As Subaru designed the engine the crank one is the only outwards breather. The two cam ones are there to suck fresh air in. If you join them to the can they can only suck dirty sir back in but of course workout the Pcv there will be no suction. So they will instead work as poor outward breathers instead.
09 April 2015, 07:42 PM
#16
It may work. But stating that the PCV system is just for emissions is incorrect. And if you read what I have written I have said all along that catch cans work and can be used just fine.
P.s. The way the PCV system works is a fact not a theory. It's written in print in the Subaru workshop manual and can be evidenced using a pressure gauge at various points in the pipe work which I have done.
I doubt many engine builders have bothered with this.
Yes your system works to remove oil vapour. Of course it does. But you have removed a system that is good for the engine. Even if it's the most ridiculously small difference (which may be outweighed by the benefit of removing oil vapours) you have still removed it. Fact.
You can only say your system appears to be working faultlessly. You can't see the effects of the acidic air building up in the block. And this issue may not even have any real negative effect but it does exist and Subaru though it wise to fit a system to combat it.
This is the problem with trying to have a sensible discussion on forums. People just say that your wrong when they don't even take in how something works.
You say trust the engine builder. I say trust the engine designer. Each to their own.
P.s. The way the PCV system works is a fact not a theory. It's written in print in the Subaru workshop manual and can be evidenced using a pressure gauge at various points in the pipe work which I have done.
I doubt many engine builders have bothered with this.
Yes your system works to remove oil vapour. Of course it does. But you have removed a system that is good for the engine. Even if it's the most ridiculously small difference (which may be outweighed by the benefit of removing oil vapours) you have still removed it. Fact.
You can only say your system appears to be working faultlessly. You can't see the effects of the acidic air building up in the block. And this issue may not even have any real negative effect but it does exist and Subaru though it wise to fit a system to combat it.
This is the problem with trying to have a sensible discussion on forums. People just say that your wrong when they don't even take in how something works.
You say trust the engine builder. I say trust the engine designer. Each to their own.
Last edited by FMJ; 09 April 2015 at 07:45 PM.
09 April 2015, 08:45 PM
#17
I admit I know nothing about the workings and the ins and outs of any car and engine but the only reason I changed to the catch can is because I snapped one of the hard plastic pipes under the inlet manifold and I wasn't prepared to fork out a load more money to what I had already spent on the car
This is how mine sits at present.
And what I ordered.
Although it has a return to sump option I have chosen to cap it. But there's always the benefit of having both options available
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