82 replies to this topic

[Alex]

theres like 3 breathers then the PCV valve ... cant be that difficult to attatch them to catch can then run one back to the intake or leave it atmo

what jim said.


why reinvent the wheel?

[Jimbo]

what jim said.


why reinvent the wheel?

i know! i know how yours is without even looking at it!

Each cam cover then the PCV and crank combined into 1 gives you 3 hoses. A fourth to link it back to the intake. DONE. If your atmo. 3 hoses in total. Its not rocket science

[zanzarah]

if the right information could be sourced this could make an interesting tech thread..... find out which breathers are the correct ones to use and put up some pics or diagrams

Excellent DIY with pics and diagrams.
http://www.ozliberty...d=5611&Itemid=3

[natho]

my concern is that the rocker cover 'vents' (as people call them) are actually fresh air inlets, at least when you're not on boost. i don't really want to be sucking oil back in from the catch can in any quantity.

here are the relevant pages from the 02 Impreza manual. i've looked at various other model liberty and wrx manuals and some have the arrows and some don't. i would have thought that the subaru manuals are trustworthy but i've found an error or two in the Gen3 manual already! i don't think there's any way for me to see if this really matters without trying it - my point is i won't just blindly trust what i read on the internet without researching it for myself.

[Alex]

So, you come onto the internet to ask people how to install a catch can, yet you don't trust them after they've installed their own?

[RX25SE]

i don't really want to be sucking oil back in from the catch can in any quantity.

Out of curiousity, how much oil are we talking about?

[B4TT]

sounds like the air from the crankcase is pretty much always blowing out, so throw a catch can on that one.

[natho]

Out of curiousity, how much oil are we talking about?

i don't know if this will happen, i was just saying that the rocker cover hoses are used for inlet and outlet. i'd imagine that if your catch can was designed properly, it'd be a small amount unless it was full.

[Jimbo]

the intake tract will always be in a state of vaccum so i cant see how the cam cover breathers would ever be an "inlet". The stock system is designed to remove vapour from the crank case and cam covers then combine those vapours with your intake air, thus burning it in the combustion process. Rigging up a catch can (atmospheric) simply takes all those vapours out of your intake and into the "catch can" to allow for a more purified mixture. If you have the catch can returning to intake, all your doing is removing a vast portion of the oil vapour from the intake but you will still get some vapour in the intake.

[natho]

the intake tract will always be in a state of vaccum so i cant see how the cam cover breathers would ever be an "inlet". The stock system is designed to remove vapour from the crank case and cam covers then combine those vapours with your intake air, thus burning it in the combustion process.

Rigging up a catch can (atmospheric) simply takes all those vapours out of your intake and into the "catch can" to allow for a more purified mixture.

If you have the catch can returning to intake, all your doing is removing a vast portion of the oil vapour from the intake but you will still get some vapour in the intake.

read the subaru text above - when the inlet manifold is in vacuum, the pcv valve is open, causing the vacuum to suck crankcase vapours into the inlet manifold. fresh air comes in via the rocker cover hoses.

[Jimbo]

and thats exactly what i said, the intake manifold is under vaccum along with the intake tract, which draws the vapours [iout[/i]. Fresh air CANNOT be drawn INTO the cam covers breather lines if there is a VACCUM acting on them. What makes you think air goes INTO the breathers on the cam covers? The only way that could happen is if there was positive pressure in your intake tract which will not happen, beacause the PCV valve is closed, and the intake tract is always under vaccum? Have a look on my diagram, the cam cover breathers arent even relative to the PCV and crank vent. All they do is come off the cam cover and go straight to the intake. When the car is at idle, the PCV valve is open which draws the vapours from the crank breather. When the intake manifold sees positive pressure, the PCV valve is closed so then the crank breather relies on the VACCUM of the intake tract to draw the vapour out.

[zanzarah]

read the subaru text above - when the inlet manifold is in vacuum, the pcv valve is open, causing the vacuum to suck crankcase vapours into the inlet manifold. fresh air comes in via the rocker cover hoses.

Blowby Solution:Litespeed incorporate one valves in their twin can set up.
https://sites.google...erformance/home

[RX25SE]

There seems to be a little confusion here regarding the operation of a PCV system. Forgive me if I am 'preaching to the converted'. Due to unburnt and burnt fuel leaking past the piston rings into the crankcase a Positive Crankcase Ventilation system is used to convert these crankcase emissions into an exhaust emission. This is done by using the negative pressure (below atmospheric or vacuum) in the inlet manifold (between the throttle body and intake valve) to draw these emissions into the combustion chamber to be burnt. Due to the fact that manifold pressure rises towards atmospheric (above in a turbo motor) as the throttle is opened, a PCV valve is used to shut off the flow of vapour when the pressure difference is small. As there is vapour being drawn from the crankcase, a vent is used to replace this lost vapour and prevent the crankcase being pulled too far below atmospheric pressure and maintain the flow of vapour. This 'inlet' is usually mounted in the rocker cover(s) and has the other end connected to the atmospheric side of the throttle body (between air filter and throttle body) or up stream (again atmospheric side) of the turbo. This provides filtered air for the engine to breathe. If the PCV system cannot cope with the large amount of vapour generated at full throttle then vapour may be exhausted from the rocker vents. This will re-enter the engine mixed with the air traveling through the normal intake tract. Hope this helps. *looks behind to discover topic has fallen off*

[Delete This Account]

I don't get it.

[RX25SE]

I don't get it.

It works in a loop.

The crankcase vapour (blowby) is sucked into the motor and replaced by 'fresh air' from the engine side of the air filter.

[LIBBY_B4]

It works in a loop.

The crankcase vapour (blowby) is sucked into the motor and replaced by 'fresh air' from the engine side of the air filter.

I know this is a really old topic and o probably sound like a fool asking this question, but as i have a b4 im curious to know what PINGING actually is?

[Soop]

Pre-ignition.

[buzzda]

What he said ^^^. Here, read THIS

[Trent]

I know this is a really old topic and o probably sound like a fool asking this question, but as i have a b4 im curious to know what PINGING actually is?

Something that your B4 almost certainly does unless it has been tuned.

[Soop]

Even then it probably does it.

I lol when I head people running 15+psi with those pee shooter turbo's.
Fan forced heaters FTL.