Crank case ventilation seems to be quite widely misunderstood in the world of Subaru powered VW conversions, and possibly in general. There are many conversions in the UK in which the standard Subaru system has been hacked using breather filters, and / or catch tanks, etc. The reason for this is almost certainly a lack of understanding of how the standard Subaru ventilation system works. Many have been installed like that bu one company. In fact it’s incredibly simple to use the standard Subaru system in VW conversions exactly as Subaru intended, at a cost of nothing or almost nothing (at most the cost of a piece of hose, assuming you have all the Subaru parts, and they are in good condition).
Rather than explaining the PCV system, we recommend you watch this video on the subject by Mr. DIYer https://www.youtube.com/watch?v=N5TCxmJPFuU . As well as explaining the history of crankcase ventilation and how they ended up with the PCV system, he also demonstrates what he is explaining with a series of experiments which make it much easier to understand. The petrol system he describes is exactly how it works on all of the normally aspirated EJ, EG and EZ series Subaru engines. The only real difference is that the with the engines being horizontally opposed, there are two PCV air intakes rather than one, to each cam cover rather then the crank case.
If you’re using our induction hoses, they all come with everything needed for the standard PCV system to work as Subaru intended (as long as you have all the Subaru parts and they are in good condition). Similarly, so does our throttle body reverser kit for Phase I engines. This is because how the PCV pipes are plumbed into the induction system in models with airflow meters is important, and this kit inlcludes the parts for plumbing the relevant bit of the induction system.
Our throttle body reverser kits for Phase II engines does not include pipework for the PCV air inlet. This is because this kit does not currently include the relevant section of plumbing (between the throttle body and air filter). Exactly where the PCV air is sourced from is mush less important on engine without airflow meters such as most of the Phase II normally aspirated models – it can come from anywhere between the air filter and throttle valve.
All of the the Subaru engines used in VW conversions use a ‘positive crankcase ventilation’, or PCV system, as do just about all modern engines. There is no downside to using it as intended, but if you’re plumbing it yourself, doing so does require
Checking a Subaru PCV valve
If you’re servicing a Subaru engine, checking that the PCV valve works as intended is not a bad idea. To do this, remove the valve and shake it. It should rattle, as the spool inside moved against the spring. A PCV valve which doesn’t rattle is usually clogged up inside, and needs either cleaning or replacing.
‘Oil Catch Cans’
This related video from the same Youtube channel explains the disadvantage of fitting an ‘oil catch can’ into the breather system. This seems to be a recent internet ‘trend’ spread by those with little to no understanding of the systems they are working on https://www.youtube.com/watch?v=hDx09voTlbw . There is no need to ever use one on a standard engine with a working PVC system. Like his PCV video, not only does Mr. DIYer explain ‘oil catch cans’ , he also demonstrates the disadvantage of attempting to use in using simple experiments.
That’s not to say there is no legitimate purpose for oil catch cans. Apparently they are required by some race series as an extra means of preventing oil escaping the engine when things go wrong from ending up on the track.
Thanks to Mr. DIYer for creating the above videos and for being OK with us linking to them.