I have been going over this exact thing for a long time now and revisited the whole PCV setup over the past few days.
Just so strange that this post shows up a day later.
During my oil change in December, also suspecting heavy carbon build up (have another post about thousands of recorded misfires), I ran a can of CRC GDI and turbo cleaner through the engine. This is about 20% PEA (polyetheramine), 30% diesel fuel #2, and other propellants. On initial run, nothing seemed to change. However, over the next few days things change dramatically. My misfire count has dropped to near nothing, and the smoothness and power from the engine has returned. Actually, it was the most powerful the little 1.2 has ever felt since I bought it. From now on every service will include a can of CRC GDI cleaner ... because clearly diesel is better for petrol cars.
Back to the catch can. I like the Mann+Hummel Provent 2 setup. I'd like to get one sometime; just broke as sin and literally close to total failure does not help.
Here are my thoughts on this so far.
Leave the valve cover breather where it is. This is your fresh air intake. I don't suspect this vents too much crankcase gases. You can confirm this by looking inside the air filter housing. There's much less gunk in there than in the charge pipe leading to the throttle from the turbo. It is not zero though, but I think this depends on how much excess pressure is in the crankcase.
The crank vent at the side of the valve cover is not only for crankcase gases. It is fuel vapour as well. Follow the line down to the throttle body and you will see a t-piece directing the fuel vapour coming from the solenoid valve. I would probably split this from the PCV system and give it its own one-way port into the turbo intake. Or effectively join it to that turbo pipe after the valve cover outlet. There is another turbo inlet pipe available that makes this simple, but that's another $100 expense.
Doing that will free up the existing turbo intake for just oil vapour.
I suspect there is not much boost pressure in effect when at highway steady cruising speeds (reasonable speeds, that is). The intake port will therefore be drawing in all the gases.
I think if you're a city driver you will constantly be in pressure mode (stop/start, many gear shifts and accelleration), making the turbo intake the prime target. The 2 valves will constantly be switching but these cars need boost.
Picking one is tuning for one.
Perhaps it is best to target both.
And by that I mean the following.
Change the catch can inlet/outlet to open T-piece connections.
On the catch can inlet, feed in the oil separator vent hose and the side valve cover vent hose.
On the catch can outlet, run hoses to the turbo intake and the intake manifold valve.
This means there is no messing with the standard one-way valves. The gas still drawn to the highest vacuum signal possible.
A question I am left with now is system response due to newly introduced hose lengths. At the same time, many catch cans have been successful using these longer hoses with no adverse operating effects. It's just that you want the system responding to vacuum properly at each port in order to avoid that top fresh air valve doing the venting.
Another thing worth looking at is improving the oil extraction efficiency of the oil separator.
This could possible be done using the stainless steel pot scourer trick many have used on other setups.
Using a stainless steel pot scourer will increase the size of the surface on which oil can accumulate.
There are several chambers in the separator. I feel like the best chamber for this is the first one after the first swirl pot. Although filling the 2nd swirl pot might make a difference too.
This must be packed in loosely to avoid increase back pressure and avoid any possible clogging.
It's an old trick used to get better filtering from a catch can.
My big concern here is metal from the scourer going back into the sump. The scourers are not small filaments and not brittle, but still a concern.
The other concern is this is not easy on maintenance at all. Removing that separator is a pain and requires sealant. Just thought I'd mention my thoughts on it.
In terms of the Mann+Hummel Provent200 I had in mind ...
1. They're not cheap, but they have overpressure safety valving installed (moved to the filter instead of the cap in the later models)
2. Their patent ran out so now you can get knock-off units and fit in the official filters. You just want the housing and it's a huge difference in price. The new filters might not work.
3. Filter lasts approx 40,000km. Not bad, but still a cost.
4. They have a venting regulator valve fitted before the exit. Given the other valves in the system, might want to remove this and just make it an open port. I am not sure though if this valve is critical to the oil separation process; it might be trying to keep some pressure in place to allow the oil to be separated rather than just use speed of flow.
5. They drain out the bottom allowing one to have a separate reservoir for catching oil, or to drain the oil back to the sump (not applicable without drilling/tapping something).
I really wish it was possible to find the matching NORMAQUICK V2 connectors used on these cars. It'd make it so much easier to build this especially when it comes to that vent on the valve cover. I looked around last year and didn't find perfect connectors.
What are your thoughts?
I have nothing better to do but over-analyze this.
Thanks to both of you!