Dual Catch Can - Why you want to do it

NoQuarter

Major
Nov 24, 2017
1,506
936
0
Indiana, USA
Ride
Z4 35is, 535xi, X5 35i
What is a dual catch can?

If you have read about the need for doing a walnut blasting to clean the valves... that is what this is all about. The cause of the dirty valves is due to the CCV dumping oily, yucky, blow-by sh$t back into the intake, across the valves and back into the engine to be recirculated instead of vented into our precious atmosphere. Furthermore, the valves do not get cleaned from fuel due to the direct injection system we have.

Many enthusiasts install a single catch can on the high pressure side only. There are a few points to be made here:

1) This is done because it certainly helps the problem
2) This is done because the high pressure side is accessible and is "easy"
3) What about the low pressure side? This is typically skipped because in our engines it is an internal system that is not readily adaptable to a catch can but is in fact the primary cause of severe fouling especially in cyl 4,5,6.

So... the low pressure side is where the second catch can in a "dual catch can" goes to trap some of the sh$t before it fouls up the valves. Our engine spends the majority of its life in low pressure PCV mode because it is not under boost most of the time hence contributes most to intake fouling.

Rob at RBTurbo can supply the parts to convert the internal, low pressure side PCV into an external PCV so that it can be routed through a catch can.


------------------------------------------------------
Some installation notes

A catch can should be as cool as possible in order to get the oil and water to condense and stay in the can as the cleaner air continues on.

This photo shows a location in a Z4 where the cans are in a cooler part of the engine bay protected by a heat shield:

6OTg533pI05Otan4_7UZF7c-zPe4jXXpxdx5zuzvnqRNpp6njEuaKJ-DRjc-Q?width=660&height=371&cropmode=none.jpg


Awuu4LRxbpEy9hgKTxKpxtSmhhQ-jO3UmDQC3ylRBpSGARwiFKYMCRcntyblQ?width=660&height=371&cropmode=none.jpg



This is where the crankcase ventilation system is.

The low pressure side has the internal PCV valve and the high pressure side is where the flapper hose assembly connects (I have already removed it in this pic)

3EZvtWhksob3Ff0XGbNQ4KpM5FspGP20QSh0EDR8ZArYHRpha0cHA87yjVdkA?width=660&height=371&cropmode=none.jpg


This one has some notes to help see what is what. Note #4 should say cyl 4,5,6.
(This is best pic I can display with the text)
O_IDSk0CaEHOUrS-dgbnFE5adiDnzmOFvco7P4x-2mbDNcTdJfh7c0nG0n1w?width=1631&height=894&cropmode=none.jpg


The External PCV is in place (see #1 above) and the flapper assembly for the high pressure side with the factory plastic pipe removed
6CcILJVyozAjKr-P818PDazpfYZ8dMyQ_eR55NboH4BNnbTNGmKV8lOG8V8QA?width=660&height=371&cropmode=none.jpg



Hose Routing. The high pressure side goes from the flapper, through a can, back into the rear turbo inlet pipe.

The new, low pressure external PCV port goes through a can then routed into the intake port.
Rob can supply a convenient adapter that gives you a connection to the intake or you can drill and tap the intake for the new line.
jFtrRxSpbNlEwpRKltbLg5K0N_kDcxGwVT-y9eUJlQo2SLX-ICPlog7BJmNwA?width=660&height=371&cropmode=none.jpg


Final note:

The low pressure side catch can is a great improvement on its own, but the solution is not 100% effective unless you go all the way. The internal PCV system routes the blow-by into the intake internally inside the valve cover and these internal passages into the intake are still open.

The ultimate step in this process includes plugging those internal passages.
If you have everything you need and are doing a valve cover gasket project, plugging these passage takes about an hour. Here is a video of the process:

 

[email protected]

Lieutenant
Dec 7, 2016
626
397
0
St. Louis, MO USA
www.rbturbo.com
Ride
'08 335i, '14 M6, '15 Tundra
Is anyone using the AD Eng catch can with his fittings to block the manifold ports and delete the flapper?

Many always seem to be confused by this and it is worth noting again: No adapter fitting threaded into this Valve Cover PCV area (upstream) can technically block off the head ports where it matters most, which is at the cylinder head surface (downstream).

On this same note our fitting does indeed "block off the head ports" (as others do too) just not affectively where it matters- once again and all together now "at the cylinder head surface".

The other point is that the OP apparently wishes to retain PCV functionality, which IMO is wise for most all street cars. But he also has gone with the external setup and at this point he can intercept the low side with an OCC; which without going external pcv you can not accomplish this feat.

Those who run PCV delete systems such as what you reference are doing away with ALL pcv functionality, which some believe is best for themselves. This is otherwise known as a VTA "Vent To Atmosphere" setup, which again deletes PCV altogether.

Rob
 
  • Informative
  • Agree
Reactions: tisdrew and langsbr

[email protected]

Lieutenant
Dec 7, 2016
626
397
0
St. Louis, MO USA
www.rbturbo.com
Ride
'08 335i, '14 M6, '15 Tundra
  • Like
Reactions: tisdrew

Jlcn54

Private
Mar 2, 2017
40
14
0
I already have rb external on the low side and bms with flapper on the high side but I want the high side to vent more since I'm close to 700whp. What can I do to make it vent better? Valve cover breather with check valve? I feel like the stock flapper is restrictive when your pushing big hp
 

[email protected]

Lieutenant
Dec 7, 2016
626
397
0
St. Louis, MO USA
www.rbturbo.com
Ride
'08 335i, '14 M6, '15 Tundra
I already have rb external on the low side and bms with flapper on the high side but I want the high side to vent more since I'm close to 700whp. What can I do to make it vent better? Valve cover breather with check valve? I feel like the stock flapper is restrictive when your pushing big hp

Going to be lots of variables here, especially when you consider potential engine/turbo health issues that could be present; but certainly there will come a power point where an all out setup is required (ie. crank vac) even if all is well.

We are not sure if your feelings are warranted or not, but if you want to make sure you could measure your crankcase pressures while under large loads and see what you have cooking. If you have some issues you are experiencing (while on RB External PCV with head ports plugged) firstly we'd start with checking the leak down of your engine, possibly a turbo inspection, once complete and all happy then determine your Crankcase pressures under full load (you can modify an oil cap as a reference source).

Our thoughts are that the OE valve cover is extremely well thought out, but it will have some limitations ventilation flow-wise at some point but we are just not sure that point has been found quite yet. The biggest issue with it is that it is plastic and thus can crack, melt, etc.; an inherent flaw that there is really no way around. Another issue is that the Low side OE Internal PCV function can have some weaknesses, but those are completely eliminated with the RB External Setup (with head plugs). All of this aside it is quite the engineering masterpiece, but indeed some testing into its ventilation abilities (or lack thereof) under very high powered scenarios would be interesting.

Rob
 
Last edited:

R Shaffner

New Member
Mar 30, 2018
1
0
0
Ride
2002 540i-6
This is a GREAT write-up. I was getting pretty confused by the different catch can set-ups. This helps a lot.

I have a few questions:
Is this problem is caused by weak oil separators that just don't do the job? Or is it that they get clogged over time, and eventually they can add oil to the blow-by gasses instead of separating it out? (Happened on my M62 and many others.) Or is it that the DI doesn't clean the intake valves, so the problem is more acute?

Or... is BMW just too focused on making negative pressure in the crankcase? When I think of many other cars, this all seems like overkill. We're just talking about blow-by gasses, which most other cars route back to the air intake up-steam of the throttle. No car needs positive pressure in the crankcase. Extra gasses and moisture need a way out. But does any car really need negative pressure in the crankcase? Why?

The intercooler acts like a catch can for that path, though no one likes the idea of a lot of oil going through the bank 2 turbo. But that's an existing way of monitoring the problem. If there's not much oil in the bottom of the intercooler, then the oil separators are probably doing ok.

I'm helping a friend with his N54, which is why I'm learning about all this. If this were my car, I'd be tempted to block off the low side completely at the PCV (block it or remove it and plug the hole) and put a catch can on the "high" side only. In other words, I'd try to reduce the oil going to the turbo, but not worry so much about creating negative pressure in the crankcase. Pretty sure any every tiny bit of higher pressure in the crankcase would vent out to the bank 2 intake easily.

I'm not saying that's the best approach. I suspect the best approach is outlined here. or one like it. But I often like giving the cheaper and easier solutions a chance to work first.

(And finally, do N55's have this problem too, or do their cam covers do a better job, and clog less?)
 

[email protected]

Lieutenant
Dec 7, 2016
626
397
0
St. Louis, MO USA
www.rbturbo.com
Ride
'08 335i, '14 M6, '15 Tundra
Is this problem is caused by weak oil separators that just don't do the job?

This is an interesting point where people get their brains WAY out of whack. They see that the cyclonic separators are not 100% effective and think "let's just rip them out what a waste". Truth be told the OE valve cover has great baffling along with ADDITIONAL Cyclonic separators and it STILL is passing some oil out through the ports, but this doesn't mean that they aren't making things better.

In making new valve covers or the like and yanking out all baffling and/or cyclonic separation all out of and putting a straight open hole up top/front/side/wherever is not going to make things better. Doing things that like will only end up with MUCH more oil being poured out and either caught by a can, or vented to atmosphere, or recycled through a PCV valve; pending on the arrangement chosen. Some baffling in valve covers goes a long way to help to contain oil in the crankcase.

The long and short of it is that this is one of those topics that everyone thinks they may have the master plan, "I'll do x/y/z" they say and many seem to ever get anything right IMO. This thread outlines a very cheap and effective way to get most all issues with the system back in check and bulletproof, but as described in my post above there could be some point power-wise where some extra provisions could be made to allow it to still work as intended yet handle the additional blowby that comes when making much more power. As we do not think this is an issue to perhaps the 700rwhp+ range it is likely a moot point in discussing much further for most N54'ers, although it would be nice to do as discussed with a healthy setup say 700+rwhp car to see if we notice any limitations in the ventilation side of the OE valve cover when arranged in this fashion.

Rob
 
Last edited:
  • Informative
Reactions: tisdrew

[email protected]

Lieutenant
Dec 7, 2016
626
397
0
St. Louis, MO USA
www.rbturbo.com
Ride
'08 335i, '14 M6, '15 Tundra
So I've got an overly simple question. If one was to plug the high and low side outlets of the cam cover, plug the six intake holes with threaded plugs, and run a VTT crank case breather ... would that work (or why wouldn't it work)?

Filippo

If you fancy no PCV system and a VTA arrangement that is fairly limited, give it a shot. Once you realize you are tired of the smell and oil mess and most likely worse CC pressure and the subsequent issues it brings with it, we'd suggest just going a route that has already been proven to work damn well for years now (ie. retain OEM like PCV functionality, or better yet externalize it along with the bulletproofing/head plugs). This area of the N54 seems to constantly being over thought, when a simple/cheap/functional solution is and has been available for such a long time now. Just keep it simple and get it done the right way the first time and move on to another project.:weary:

Rob
 

fmorelli

Major General
Staff member
Aug 11, 2017
3,125
2,834
0
54
Virginia
www.morelliguitars.com
Ride
E89 Z4 35i, F10 535d
If you fancy no PCV system and a VTA arrangement that is fairly limited, give it a shot. Once you realize you are tired of the smell and oil mess and most likely worse CC pressure and the subsequent issues it brings with it, we'd suggest just going a route that has already been proven to work damn well for years now (ie. retain OEM like PCV functionality, or better yet externalize it along with the bulletproofing/head plugs). This area of the N54 seems to constantly being over thought, when a simple/cheap/functional solution is and has been available for such a long time now. Just keep it simple and get it done the right way the first time and move on to another project.:weary:

Rob
It was a curiosity question. That said, you have an email from me last night asking about putting an order together to wrap up my PCV system. I'll await your reply to that email. Thanks.

Filippo
 

The Convert

Captain
Jun 4, 2017
1,482
1,038
0
Ride
335
It was a curiosity question. That said, you have an email from me last night asking about putting an order together to wrap up my PCV system. I'll await your reply to that email. Thanks.

Filippo
I think you should just go dry sump setup and then you'll never have any more cc issues or potential turbo oil drain issues. Plus, I'd love to see/own a dry sump N54.
 

[email protected]

Lieutenant
Dec 7, 2016
626
397
0
St. Louis, MO USA
www.rbturbo.com
Ride
'08 335i, '14 M6, '15 Tundra
It was a curiosity question. That said, you have an email from me last night asking about putting an order together to wrap up my PCV system. I'll await your reply to that email. Thanks.

Filippo

It is just 2 trains of thought.

1) Punch holes all over your crankcase and hope it vents well. Deal with smell, oil mess, etc. simultaneously. Not even a tidbit vacuum assist will ever be had.

2) Retain PCV which retains vacuum functionality via Intake manifold vacuum reference at low loads, and turbo inlet vacuum reference at high loads. No smell, no mess, etc.

Quite frankly even a healthy OEM system would be more ideal than most of these other solutions out there, so just keep it as is and healthy if need be and/or extreme budget is a factor.

Rob
 
  • Like
Reactions: seb.apprenti