Ok, so here's my 2c on the commercially available OCCs on "this" platform and I'll post this up in the other recent OCC threads we have going
This is after reading half the internet available on PCV systems outthere over the past few days lol
PCV systems are designed with vacuum in mind because that vacuum is crucial to the operation of the engine and it also impacts power delivery...crankcase pressure is something that should be considered seriously before playing with today's N54 OCCs, stress the word "seriously" here...if a restrictive OCC is introduced it can lead to both engine (valve stem seals) and turbo (seals) damage...Restrictiveness is introduced by things like the following:
1) Smaller than stock diameter tubing
2) Much much much, ok well about 4-5x, longer than stock PCV tubing
3) 90deg bends at the PCV outlet
4) Baffling used inside the OCCs
5) Irregular maintenance of the OCC
6) Oil buildup in the long tubing leading in/out of the OCC over time
Some of these are addressed by today's commercially available OCCs but some are not and some just can't due to location/placement of the PCV outlet at the back of the engine.
On top of all this there's a topic of venting to atmosphere through a tiny crankcase filter. It is definitely not the way to go as the vacuum serves a crucial purpose of pulling vapours/pressure out of the crankcase. Not doing this has shown real world performance losses (thanks to Hotrod for testing this with a vbox). If you do some google-ing you'll soon realize just how critical it is to have this vacuum in your PCV system.
In summary, my opinion after researching the heck on this topic (and obviously those in the know please comment back) I've come to realize that all of today's popular and commercially available N54 OCCs and their designs are inadequate. What I'd like to have from my OCC designer is the following before putting another OCC on my car:
1) Flow rate out of the stock N54 PCV outlet under boost (positive pressure) and the amount of vacuum pulled when not under boost
2) How the above is changed by introducing their OCC and long tubing under boost and vacuum conditions
This community needs to realize that something as simple as an OCC isn't something that should be taken lightly as a lot of people, including myself, have take it to be. I had run the RR OCC for about 2.5 years now. It leaked all over the place and it didn't collect oil almost at all. It would collect maybe 2mm at the bottom of a can after about 10,000km of mixed hard/regular driving. This isn't something that I'm willing to risk instead of the stock PCV setup. I made a mistake buying the BSH OCC just 2 weeks ago and not researching this topic more thoroughly while relating it to the N54 PCV design. What drives me nuts sometimes is certain vendors totally misrepresenting OCCs to this community with pics of tons of blowby caught by them when its very clearly not the case on the N54. Yes, there's blowby, but NO there's isn't even 2% in vast majority of cases as what they're showing. The pics they show are from the VW/Audi engines that have massive amounts of blowby. I know this first hand as I've personally witnessed a BSH OCC being emptied on a 2010 VW GTI. Its ridiculous on that engine but this just isn't the case here.
I'm going stock PCV setup starting today until a more proper setup addressing the above arrives for the N54...the tiny amount of blowby from the N54 on my car is definitely more welcome than risk of damaged turbo(s) or damaged say valve guide seals..This is especially a concern with guys running high boost occasionally or those with upgraded turbos..