Catch Can 2 or 3 Port?
23 February 2015, 11:18 AM
#1
Catch Can 2 or 3 Port?
I have a 2 port catch can and looking to plumb it in but unsure of connecting heads and block breathers together before they get to the can.
Will this give a pressure difference thus back feed into the heads?
Am I better off with a three port?
Does everyone vent to atmosphere or recirc to the intake pipe?
Will this give a pressure difference thus back feed into the heads?
Am I better off with a three port?
Does everyone vent to atmosphere or recirc to the intake pipe?
23 February 2015, 12:15 PM
#2
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2 port is better than none, 3 port better than a 2 port.
Where you vent the crankcase gasses to depends on how fussy you are. If you are feeding CC gases loaded with oil vapour back into your inlet tract you are effectively lowering your octane rating and increasing the chances of det.
Where you vent the crankcase gasses to depends on how fussy you are. If you are feeding CC gases loaded with oil vapour back into your inlet tract you are effectively lowering your octane rating and increasing the chances of det.
24 February 2015, 01:05 AM
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The only can I've seen with a decent filter in the can is the Mishimoto one, but that costs an arm and a leg!
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24 February 2015, 08:17 AM
#8
The system requires a vacuum to draw air up the pipe work into the can, running to atmosphere never really works. You really need to send the 'dirty' air though a corze to separate the oil. Many pics of this on google. All three port cans I have seen are sealed units that you cant put corze in (Apart from Mishimoto).
24 February 2015, 08:39 AM
#9
The system requires a vacuum to draw air up the pipe work into the can, running to atmosphere never really works. You really need to send the 'dirty' air though a corze to separate the oil. Many pics of this on google. All three port cans I have seen are sealed units that you cant put corze in (Apart from Mishimoto).
24 February 2015, 08:40 AM
#10
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You don't need a vacuum. The crankcase will be under positive pressure most of the time because of combustion gases that escape past the piston rings.
24 February 2015, 09:06 PM
#12
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I run a single 3 port can wich is baffled & VTA
A single head breather either side & direct CC ventilation ( no PCV
Works just as it should , winter & cold months fills with water
Hard driving summer oil residue ..
In winter I empty it every fortnight as the cold is unpredictable at how much condensation & water it acumilate's... The 1 drawback for me ( if you can call it that ) is I may tap the top thread out to enable a bigger filter vent ,
A single head breather either side & direct CC ventilation ( no PCV
Works just as it should , winter & cold months fills with water
Hard driving summer oil residue ..
In winter I empty it every fortnight as the cold is unpredictable at how much condensation & water it acumilate's... The 1 drawback for me ( if you can call it that ) is I may tap the top thread out to enable a bigger filter vent ,
25 February 2015, 12:48 AM
#15
The following is my thoughts (with a lot of research) on the system. Catch cans are a good thing. But the way most people impliment them (IMO) is wrong. VTA may be good for preventing oil air in the intake but its bad for engine breathing.
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 ways the crank vent can vent are all connected to system post MAF is 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.
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 ways the crank vent can vent are all connected to system post MAF is 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.
25 February 2015, 01:21 PM
#18
Took a bit of finding but rather then be doubted
Here:
http://www.google.co.uk/imgres?imgur...d=0CFsQMygwMDA
With regards to vacuum in the crank case.... then how could fresh air be drawn into as per the tech info above? If there is no vacuum then no air would be drawn in. There is no pressure in the intake pipe to force its way into the heads and then crank so it has to be vacuum. Or did Subaru design the engine without understanding how it worked?
Also I have tested with a pressure gauge on various points in the breather system and found that you do get vacuum in the hoses due to the PCV valve (obvious really as its a one way valve attached to the inlet manifold which on closed throttle has about -20 on the boost gauge).
The crank case itself might not be under complete vacuum as pointed out. But that doesn't mater. I am not saying that. I am saying that the PCV system sucks on the crank case and pulls **** air out. The same way if I were to hoover my living room the room wouldn't suddenly became a vacuumed spaced but air would be sucked in all the same. Admittedly in that example the hoover would put the air back into the same room but you could just as easily see the principle if the hoover were outside and the hose through a hole in the wall.
Like I said i am sure lots of people run VTA and catch cans with no issue. But I will stick to the OE system or better the OE system with in line catch cans which retain the PCV system to keep air moving through the engine as it was designed by Subaru.
Here:
http://www.google.co.uk/imgres?imgur...d=0CFsQMygwMDA
With regards to vacuum in the crank case.... then how could fresh air be drawn into as per the tech info above? If there is no vacuum then no air would be drawn in. There is no pressure in the intake pipe to force its way into the heads and then crank so it has to be vacuum. Or did Subaru design the engine without understanding how it worked?
Also I have tested with a pressure gauge on various points in the breather system and found that you do get vacuum in the hoses due to the PCV valve (obvious really as its a one way valve attached to the inlet manifold which on closed throttle has about -20 on the boost gauge).
The crank case itself might not be under complete vacuum as pointed out. But that doesn't mater. I am not saying that. I am saying that the PCV system sucks on the crank case and pulls **** air out. The same way if I were to hoover my living room the room wouldn't suddenly became a vacuumed spaced but air would be sucked in all the same. Admittedly in that example the hoover would put the air back into the same room but you could just as easily see the principle if the hoover were outside and the hose through a hole in the wall.
Like I said i am sure lots of people run VTA and catch cans with no issue. But I will stick to the OE system or better the OE system with in line catch cans which retain the PCV system to keep air moving through the engine as it was designed by Subaru.
25 February 2015, 01:57 PM
#19
So the following is the ideal method:
Two catch cans one for heads/cams and one for crankcase. Plumbed from both heads to can (though gauze etc), then to the intake pipe. Crankcase to can then to intake. This will keep the system as close to original spec as possible. With in essence in-line filters.
But if you were to run a three port can you have the one vent run back to intake pipe. This single pipe will complete the circuit from the can, recirculating for all three input (crank and cam vent pipes). Is this possible to run only one return to intake from all the breathers?
Some awesome responses on here, nice
Two catch cans one for heads/cams and one for crankcase. Plumbed from both heads to can (though gauze etc), then to the intake pipe. Crankcase to can then to intake. This will keep the system as close to original spec as possible. With in essence in-line filters.
But if you were to run a three port can you have the one vent run back to intake pipe. This single pipe will complete the circuit from the can, recirculating for all three input (crank and cam vent pipes). Is this possible to run only one return to intake from all the breathers?
Some awesome responses on here, nice
25 February 2015, 03:13 PM
#20
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With regards to vacuum in the crank case.... then how could fresh air be drawn into as per the tech info above? If there is no vacuum then no air would be drawn in. There is no pressure in the intake pipe to force its way into the heads and then crank so it has to be vacuum. Or did Subaru design the engine without understanding how it worked?
25 February 2015, 03:23 PM
#21
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To the OP, for what it's worth, my 4 port CC was installed by Zen Performance, and they know a thing or two about engines.
Two ports are connected one each side to the cam cover breather (and be careful which one you use as there are two on newage covers).
The third port is connected to the PCV on the crankcase.
The fourth (exhaust) port is just a VTA exit under the car.
Nothing is used to draw air through the CC and there's no crap getting into the inlet tract.
Take it or leave it, but it works.
You don't need 3 inlet ports on your catch can. You can easily tee the cam cover breathers into one port.
Mine also has a return to sump line, but that's a different argument to have another day.
Two ports are connected one each side to the cam cover breather (and be careful which one you use as there are two on newage covers).
The third port is connected to the PCV on the crankcase.
The fourth (exhaust) port is just a VTA exit under the car.
Nothing is used to draw air through the CC and there's no crap getting into the inlet tract.
Take it or leave it, but it works.
You don't need 3 inlet ports on your catch can. You can easily tee the cam cover breathers into one port.
Mine also has a return to sump line, but that's a different argument to have another day.
25 February 2015, 05:03 PM
#24
To the OP, for what it's worth, my 4 port CC was installed by Zen Performance, and they know a thing or two about engines.
Two ports are connected one each side to the cam cover breather (and be careful which one you use as there are two on newage covers).
The third port is connected to the PCV on the crankcase.
The fourth (exhaust) port is just a VTA exit under the car.
Nothing is used to draw air through the CC and there's no crap getting into the inlet tract.
Take it or leave it, but it works.
You don't need 3 inlet ports on your catch can. You can easily tee the cam cover breathers into one port.
Mine also has a return to sump line, but that's a different argument to have another day.
Two ports are connected one each side to the cam cover breather (and be careful which one you use as there are two on newage covers).
The third port is connected to the PCV on the crankcase.
The fourth (exhaust) port is just a VTA exit under the car.
Nothing is used to draw air through the CC and there's no crap getting into the inlet tract.
Take it or leave it, but it works.
You don't need 3 inlet ports on your catch can. You can easily tee the cam cover breathers into one port.
Mine also has a return to sump line, but that's a different argument to have another day.
Cheers, was just concerned that by 'blanking' off the inlet and VTA then there wouldn't be a sufficient vacuum to make it effective. How much do you accumulate in the can using VTA?
how the hell i miss that!!
25 February 2015, 05:34 PM
#27
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As I said make sure you use the correct port on the cam covers. I don't know all the variations, but on my 05 car the covers have a 12mm and a 15mm port. The natural choice is to use the 15mm port, but this doesn't have a splash shield like the 12mm port does to prevent oil being blown (note by Positive Crank Case Pressure) or sprayed out of the cam casing.
25 February 2015, 06:25 PM
#29
Thanks for the heads up. I have already reconnected everything after installing a FMIC, so will take direct from them (assuming that this is the correct one as similar to you there is two ports).
Regarding the crankcase breather pipe did you take the one that runs from the PCV to the intake pipe (pre turbo) to the can? and leave the one running from PCV to intake manifold as it is?
Regarding the crankcase breather pipe did you take the one that runs from the PCV to the intake pipe (pre turbo) to the can? and leave the one running from PCV to intake manifold as it is?
25 February 2015, 06:28 PM
#30
As I said make sure you use the correct port on the cam covers. I don't know all the variations, but on my 05 car the covers have a 12mm and a 15mm port. The natural choice is to use the 15mm port, but this doesn't have a splash shield like the 12mm port does to prevent oil being blown (note by Positive Crank Case Pressure) or sprayed out of the cam casing.
The 15mm un baffled ports on the cam covers is only a crankcase to heads breather balancing system, which connects to the 15mm port on the r/h side in the middle of the block, if these are used as a breather to catch can the sump will empty quite quickly, seen quite a few failed engines connected like this.