UPDATE (July 27, 2011):
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No idea how I/we missed the fact that the AR OCC is right in BMW spec, with upgraded turbos on the car, as stated in the Bentley service manual...in fact, running without the AR OCC and on the stock PCV setup makes the car go into vacuum (as shown in the data in this thread) when the expected crankcase pressure, again according to Bentley BMW N54 specs, is between 2.8-4.4" of H2O...Here's the source of some of the recent discussion on the topic:
http://www.e90post.com/forums/showpo...7&postcount=63
The BSH OCC is also very close to spec, just borderline out of spec due to just slightly larger crankcase pressure (1" H2O)...that is with upgraded turbos...with stock turbos I'd say that it'd be within the BMW spec and is perfectly safe to use...
In summary, both BSH and AR OCC are safe to use with the upgraded (RB) turbos as their crankcase pressure under WOT conditions is within BMW specs..on stock turbos, which haven't been tested for crankcase pressure, I'd expect both OCCs to be even tighter within BMW spec
Enjoy your BSH and AR OCCs ppl, they work just fine...
My personal vote/preference, on upgraded turbos, goes to the AR OCC driver's side mounted version
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Thought I'd start a new thread and not pollute the BSH OCC thread with PCV discussion so no one gets offended
lol The post below is copied right from the BSH OCC discussion thread so for any prior feedback please refer to the following post (you can go a few pages into it when it starts to get into PCV discussion):
http://www.e90post.com/forums/showthread.php?t=513999
Here's a diagram of the N54 PCV system to start off the discussion with:
There are 2 checkvalves, in the diagram #2 and #3..unless you're running VERY high boost and upgraded turbos you probably don't even need to read this post
Here we go:
- if functional, cv#2 is open under boost (acceleration) and "vents" air out of the crankcase with any blowby, oil vapours. It is CLOSED in all other conditions. Let's call this cv the OCC checkvalve as that's what most people know about today as OCCs hook up on them.
- if functional, cv#3 is open under vacuum (idle, cruise, deceleration) and sucks air out of the crankcase, through the cyclonic BS in the valve cover and in it goes into the intake manifold, and goes right through your intake valves and gets burned off. It is CLOSED in all other conditions. Lets call this checkvalve the intake manifold checkvalve. This is THE checkvalve we've just started talking about past few days, not many people have ever discussed it and no one ever hooks anything up on it as its vacuum based.
So, the two checkvalves operate in different situations, one is under BOOST other is VACUUM.
So, to have crankcase overpressure "issues" 2 things can happen (both are possible but 2nd is much more likely):
1) You "can" get OVERpressure when/if CV#2 remains closed open under boost OR whatever is hooked up on it is restrictive (like a restrictive breather, OCC). Both of these are bad. Likelyhood of CV#2 clogging or not opening for any reason is EXTREMELY low. I know this by looking at it. So no issues with keeping it in place. What needs to be investigated here is CFM out of the crankcase under boost and compare that to how restrictive alternative setups are (OCC, breather, VTA). They might be just FINE! but given no OCC vendor has ever published ANY data, we have no idea..willing to risk it with your car? sure, your car, myself been guilty of this for 2.5 years
now I'm trying to actually understand it with some data
2) You "can" get OVERpressure when/if CV#3 leaks under boost. Now, this one MUST stay CLOSED under boost which theoretically it "should". If its NOT closed as it should be, what do you think happens? It allows air to leak into the crankcase from the intake manifold (which is under positive pressure/boost). This causes 1) a boost leak 2) crankcase to pressurize with air that was meant to go into your engine instead of bypass it and enter the crankcase through this damn little checkvalve
Keep in mind BMW designed this system with stock turbos in mind and much much lower boost than some of us are willing to run on these cars
How and why do I suspect checkvalve#3 to be prone to leaks under boost? Given some failures of turbo seals, various gaskets on cars especially with higher boost applications, and myself on my car noticing oil leaks all over my engine recently, ONLY when under high boost, I'm strongly suspicious of the operation of this. I washed down my engine bay, lowered boost, and no oil leaks anywhere after extended runs/pulls.
The only conclusion I can draw from all of the above is that CV#3 is leaking when under very high boost, causing crankcase overpressure which causes oil to go past various seals on the car (turbo, engine) which is B-A-D!
I've written all of this before and this time I really really tried to explain it as well as I can. If anyone has any further questions I'll refer them back to this post as I really can't explain it any better. Anyone still confused after reading this just try reading it again it'll eventually click. Referring to the diagrams posted also helps when reading it...
Now, there's no BEST solution here. There are only options. VTA is illegal and smelly but max performance is provided due to great seals under boost, and there's next to no maintenance. OCC/closed setups are legal, not smelly but maintenance is required and performance is not maximized as sealing isn't maximized.
Also, when it comes to strictly horsepower, vacuum is critical. Now, this isn't the vacuum that CV#3 provides in stock form. Its also not vacuum from cv#2 as that one doesn't have ANY in the first place. This would be a vacuum provided by an additional aftermarket vacuum pump hooked onto the valve cover somewhere (maybe that's on top of checkvalve#3, but maybe not). This vacuum needs to be applied even when accelerating/boosting, and a vacuum pump would do this job. It would ensure a good engine seal everywhere and when your engine seals really well it makes much better power. A big trick here is to "know" how much vacuum to pull as there is a thing called "too much" vacuum that can also be damaging. But this part of the story we can look at solving later...
EDIT: Actually if someone is willing to help me recommend a vacuum pump setup that'd assist in providing good seal to this engine under boost that'd be awesome...looking for pump recommnendation, how to set it up, possible mounting location, where to hook it into the valve cover, etc etc.