Is venting your crankcase bad for your tune?
Feb 8, 2007, 04:11 PM
#16
The water and acids that are products of combustion can theoretically result in degradation of oil quality, sludging and corrosion without vacuum assisted ventilation. So I would fit a baffled tank in-line in the front breather to turbo inlet pipe circuit to catch some of the oil mist that is chucked into the inlet under boost to try to keep the inlet tract clean and avoid the reduction in octane that oil mist can cause.
Presumably though there is some baffling already in the valve cover? Anyone looked?
Presumably though there is some baffling already in the valve cover? Anyone looked?
Feb 8, 2007, 04:27 PM
#18
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there is baffling in the valve cover to prevent excess oil from being dumped into the breather hose under boost, and hard cornering.
I did a lot of logging while trying to make my decision on whether or not to run a simple breather, or weld a bung on my intake pipe (my aftermarket pipe didn't come with a bung) for the fresh air makeup.
Long story short, logging showed a very minimal affect on fuel trims by running a breather instead of venting back into the intake pipe. I was still easily able to control at 14.7:1 at idle, the fuel trims changed just a tiny bit. Not enough to effect the tune or need any "retune". I went the breather route. When stopping after a good boost run, when airflow through the engine compartment is minimal, you can smell the crankcase gasses that were pushed out due to blowby past the piston rings, but that's the only drawback I can see. the engine, they fill the engine compartment and get sucked into your
I did a lot of logging while trying to make my decision on whether or not to run a simple breather, or weld a bung on my intake pipe (my aftermarket pipe didn't come with a bung) for the fresh air makeup.
Long story short, logging showed a very minimal affect on fuel trims by running a breather instead of venting back into the intake pipe. I was still easily able to control at 14.7:1 at idle, the fuel trims changed just a tiny bit. Not enough to effect the tune or need any "retune". I went the breather route. When stopping after a good boost run, when airflow through the engine compartment is minimal, you can smell the crankcase gasses that were pushed out due to blowby past the piston rings, but that's the only drawback I can see. the engine, they fill the engine compartment and get sucked into your
Feb 8, 2007, 06:21 PM
#21
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to add: after a hard boost run, with outside air lined up to the a/c in the cabin, you can smell the crankcase fumes. So obviously I'm experiencing some blow-by, which is totally normal, just not enough to make it drip off the breather.
Last edited by dubbleugly01; Feb 8, 2007 at 06:25 PM. Reason: to add:
Feb 8, 2007, 07:21 PM
#22
You may just be seeing enough pressure from blowby getting past the rings to be vaporizing the oil as it passes through the breather filter. That's what you're smelling. It's not hard to weld a nipple on your intake pipe so that the system can work as intended.
Feb 8, 2007, 07:35 PM
#23
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I drilled and tapped my intake pipe and reconnected my exhaust side breather to it.
My idle trims needed to be adjusted as expected.
Originally I had to compensate for this by raising my MAF scaling values up from 145 to 200.
Now I have them set around 180.
So yes, it seems that having the crankcase vent to atmosphere will cause your trims to increase because of unmetered air coming in.
My idle trims needed to be adjusted as expected.
Originally I had to compensate for this by raising my MAF scaling values up from 145 to 200.
Now I have them set around 180.
So yes, it seems that having the crankcase vent to atmosphere will cause your trims to increase because of unmetered air coming in.
Feb 8, 2007, 07:54 PM
#24
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Bingo
The water and acids that are products of combustion can theoretically result in degradation of oil quality, sludging and corrosion without vacuum assisted ventilation. So I would fit a baffled tank in-line in the front breather to turbo inlet pipe circuit to catch some of the oil mist that is chucked into the inlet under boost to try to keep the inlet tract clean and avoid the reduction in octane that oil mist can cause.
Presumably though there is some baffling already in the valve cover? Anyone looked?
Presumably though there is some baffling already in the valve cover? Anyone looked?
https://www.evolutionm.net/forums/sh...d.php?t=200793
Feb 8, 2007, 08:03 PM
#25
This is probably one of the most overlooked problems because some people don't understand the operation of the PCV system or because they buy intake pipes from vendors like Buschur that tune mostly with speed density and don't use a MAF.
You should NOT vent your valve cover with a MAF based system. Let me explain why. I know I have explained this a few times in the past, but since this thread is dedicated to that, maybe it will be good for the archives.
Your valve cover has a PCV valve going to the intake manifold and a breather hose (straight through fitting) that connects to the intake pipe after the MAF.
Under conditions of vacuum in the intake manifold, like idle and cruise (anytime your boost gauge shows vacuum), the PCV valve opens. The vacuum from the intake manifold is used to scavenge excess cranckcase pressure, moisture, and gases to be burned back in the cylinders. The breather hose on the other side of the valve cover is there to provide clean, fresh, metered air after the MAF to mix with this mixture of moisture, crankcase pressure, gases, etc.
So, you can think of the path like this:
(1)Air comes in through your air filter, (2)through and counted by MAF, (3)through the breather hose, (4)into breather fitting, (5)through and under valve cover to mix with gases, (5)out of valve cover through PCV valve, (6)and then into intake manifold and finally cylinder to get burned.
The problem is that when you disconnect this breather hose and vent the valve cover from this fitting is that the air is now not metered. You are bypassing steps (1) and (2). So now your MAF has no idea of that extra air being consumed by your engine. So, you fueling will be lean. The front o2 notices this and corrects by making your fuel trims positive. How much positive depends on how much air is actually being drawn into your valve cover uncounted.
This is what messes up your fuel trims and why you shouldn't vent your valve cover with a MAF based system. You can still use a catch can in line with your breather hose, but the hose should be connected after the MAF to your intake pipe still.
Eric
You should NOT vent your valve cover with a MAF based system. Let me explain why. I know I have explained this a few times in the past, but since this thread is dedicated to that, maybe it will be good for the archives.
Your valve cover has a PCV valve going to the intake manifold and a breather hose (straight through fitting) that connects to the intake pipe after the MAF.
Under conditions of vacuum in the intake manifold, like idle and cruise (anytime your boost gauge shows vacuum), the PCV valve opens. The vacuum from the intake manifold is used to scavenge excess cranckcase pressure, moisture, and gases to be burned back in the cylinders. The breather hose on the other side of the valve cover is there to provide clean, fresh, metered air after the MAF to mix with this mixture of moisture, crankcase pressure, gases, etc.
So, you can think of the path like this:
(1)Air comes in through your air filter, (2)through and counted by MAF, (3)through the breather hose, (4)into breather fitting, (5)through and under valve cover to mix with gases, (5)out of valve cover through PCV valve, (6)and then into intake manifold and finally cylinder to get burned.
The problem is that when you disconnect this breather hose and vent the valve cover from this fitting is that the air is now not metered. You are bypassing steps (1) and (2). So now your MAF has no idea of that extra air being consumed by your engine. So, you fueling will be lean. The front o2 notices this and corrects by making your fuel trims positive. How much positive depends on how much air is actually being drawn into your valve cover uncounted.
This is what messes up your fuel trims and why you shouldn't vent your valve cover with a MAF based system. You can still use a catch can in line with your breather hose, but the hose should be connected after the MAF to your intake pipe still.
Eric
And one more thing, the system also maintains a negative pressure on the head in respect to the crankcase.
I have to trap mine before the plenum or else oil goes into the #1 cyl and I get a stain on the bumper - a metaphor would be lacking fiber in diet (stained underwear)
Feb 8, 2007, 08:09 PM
#26
[quote=jcsbanks;3953587] try to keep the inlet tract clean and avoid the reduction in octane that oil mist can cause.[quote]
Very, very interesting you said that, I was knocking a little this afternoon I couldn't for the life of me find out why. Later I noticed my second trap (first one was full in a series of two right behind PVC check vlv) started getting oil accumilation.
Cleaned it and knock is gone!
This is the 2nd time I noticed this
Putting oil back into gas is turning it into the low octane precurser it was fractioned from
Very, very interesting you said that, I was knocking a little this afternoon I couldn't for the life of me find out why. Later I noticed my second trap (first one was full in a series of two right behind PVC check vlv) started getting oil accumilation.
Cleaned it and knock is gone!
This is the 2nd time I noticed this
Putting oil back into gas is turning it into the low octane precurser it was fractioned from
Feb 8, 2007, 08:24 PM
#27
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[QUOTE=C6C6CH3vo;3954671][quote=jcsbanks;3953587] try to keep the inlet tract clean and avoid the reduction in octane that oil mist can cause.
Very, very interesting you said that, I was knocking a little this afternoon I couldn't for the life of me find out why. Later I noticed my second trap (first one was full in a series of two right behind PVC check vlv) started getting oil accumilation.
Cleaned it and knock is gone!
This is the 2nd time I noticed this
Putting oil back into gas is turning it into the low octane precurser it was fractioned from
Have you checked your turbo inlet piping and intercooler piping? Where do you think all that oil vapor is going when under boost? By your post it sounds like you have a catch can between the cam cover and the intake manifold, but what about between the cam cover and your intake pipe?
Between pulling the intake piping to replace turbos, intercoolers, routine maintenance, etc., I'd rather "smell" that oil vapor/water/acid than have it end up in my intake track!!!! 
Different strokes for different folks is what makes the world go round.
Very, very interesting you said that, I was knocking a little this afternoon I couldn't for the life of me find out why. Later I noticed my second trap (first one was full in a series of two right behind PVC check vlv) started getting oil accumilation.
Cleaned it and knock is gone!
This is the 2nd time I noticed this
Putting oil back into gas is turning it into the low octane precurser it was fractioned from
Between pulling the intake piping to replace turbos, intercoolers, routine maintenance, etc., I'd rather "smell" that oil vapor/water/acid than have it end up in my intake track!!!!
Different strokes for different folks is what makes the world go round.
Feb 8, 2007, 09:02 PM
#29
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Is it safe to say then, that if you vent your valve cover to atm, then you should eliminate your pcv valve? I eliminated mine on both my 1st and 2nd gen DSMs back in the day.
Kyle Deiwert
Kyle Deiwert
Feb 9, 2007, 03:14 AM
#30
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DC3....One can for both conditions -- boost and vacuum (manifold and PCV)....I also mounted mine under the stock airbox for stealth factor and ease of draining at every oil change.