Doing a new build - forged at approximately 15 PSI. Catch can of course. What the opinion on changing to the ZO6 crankcase vent system? Worth the time/money?

Thanks

 

bump

 

ttt

 

In short, no. While it was a better option for a stock engine, it wasn't even good enough for a hard driven car at stock power levels.

With a catch can your not going to use that port anyway.

 

You seem to be up to speed on the crankcase ventilation. Can you direct me to a proper diagram for a catch can install. Ask 20 people get 10 different answers. I found several diagrams online and some of them do use the valley vent. I even considered using old school extractors hooked into the valve covers and plumbed into the header collector with a one way valve using header vacuum to extract fumes/pressure.. Works pretty well but not so good for the environment.

 

See if this helps. I plan on doing the LS6 single catch can OFF ROAD ONLY and venting the can to atmosphere (not back to throttle body like the diagram shows).

The Valve cover will draw fresh air from my supercharger inlet air filter.

Catch Can routing.pdf

 

Finally, a routing and can setup that makes sense to me. I must be hard headed but some of the setups I'v seen just don't seem like they would work well. I'm old and old school

 

when you are working with the stock hose provisions adding a check valve for boost is a good thing, but something else boost brings is additional horsepower, and that is something GM did not design the stock vent system to work with.

also you did not mention what is making the boost, but if it is turbo or centri-sc the diagram attached previously will immediately fail your main seal(s)

if you have any questions specific to what i do differently and why. i am happy to help.

my solution for this is called my C5/6 Wild system.
https://www.mightymousesolutions.com...page/c5-6-wild

 

Please expand on this.

 

boost is being fed to the passenger cover any time you are connected to the throttle body hose barb, and the throttle body is boosted. you also cannot *fix* this half of the system with a check valve like you can the foul side, as you would be stopping PCV fresh air supply during non-boost operation.

many of the configurations in that pdf are totally a bad idea IMO; but just follow the can manufacturers instructions closely.. using 'random' ones off the internet is asking for trouble.

 

Thanks for the reply. But I have a question in my mind - why is a fresh air supply need to the crankcase? In any situation I can think of the crankcase is under pressure, even at idle. There is enough blow-by to always create pressure - no? So why is fresh air required when the blow-by is constantly creating a a new air supply to the crankcase? I can't think of a situation where the crankcase would be under vacuum and require an air supply other than blow-by.

 

the pcv system runs on a regulated intake manifold vacuum source

the open end / fresh air / clean side is to let clean air in to replace dirty air being drawn out to manifold (crankcase filtration process) and to provide an escape path for high load blow-by.

this open end connects post-maf sensor on maf equipped cars so that during the vacuum cycle the air that is used (and ultimately ends up with the rest of the intake air in the manifold) is also measured.

 

Must be above my head. I still don't understand how a vessel (crankcase) that is constantly under pressure (blow-by) can need or even pull in fresh air. What pulls the fresh air in if the crankcase is pressurized? If there were a pressure and then a vacuum cycle I could understand the make-up air but even at idle with 8 cylinders pressurizing the crankcase and constantly introducing new air from above the pistons how can make-up air be "pulled in"?

 

For an NA car...

If there's no fresh air intake, the crankcase fills with blow-by (exhaust gas, basically) and the intake manifold sucks out what it can. But the crankcase gas is pretty much 100% blow-by (exhaust gas, some air, some raw fuel).

If there is a fresh air intake, there is a constant flow of air through the case, drawn by the intake manifold. Of course there's almost no draw at full throttle, but there's some flow at idle and part-throttle. But the case contents are a mix of fresh air and blow-by. I'm not sure about this but I think that emissions rules require the fresh air inlet so that blow-by gets continuously sucked through the engine and burned, rather than just accumulating and seeping into the atmosphere when the engine is stopped.

For a boosted car...

It's more complicated because the intake manifold alternates between lower-than-atmospheric and higher-than-atmospheric pressure. My Subaru's stock system has two modes of operation - with intake manifold vacuum, it pulls from the crankcase center port and fresh air comes in via breathers on both heads, with the supply coming from a post-MAF, pre-turbo fitting, so that the intake vacuum is only pulling in metered air (and blow-by). Under boost, the intake manifold check-valve closes, and both heads and the center case port all vent exhaust gas to that same post-MAF, pre-turbo fitting. There's a T-valve above the case port with one leg going to the intake manifold and the other going to the pre-turbo fitting, with a restriction on the pre-turbo line so that intake vaccuum mostly pulls from the case rather than from the turbo inlet (which would defeat the crankcase ventilation aspect). There are diagrams here if you're curious about how an OEM does PCV with forced induction:
http://www.iwsti.com/forums/2-5-lite...ns-thread.html

Lots of Subaru people just configure all three case ports as outflow vents, going into a catch can and then to that post-MAF, pre-turbo fitting. Being post-MAF, it is unmetered, but it's also either exhaust gas (no free oxygen), or unburned air/fuel mix (oxygen balanced with fuel), so it doesn't affect AFR enough to matter.

IMO the ideal setup would work similarly to the OEM Subaru setup but with two catch cans - one attached to the intake manifold to collect crap when the you're driving in vaccum, and one attached to a fitting behind the air filter, to collect crap when you're driving in boost. That's a lot of plumbing though.

 

Work with me here. You said "
If there's no fresh air intake, the crankcase fills with blow-by (exhaust gas, basically) and the intake manifold sucks out what it can. But the crankcase gas is pretty much 100% blow-by (exhaust gas, some air, some raw fuel).

If there is a fresh air intake, there is a constant flow of air through the case, drawn by the intake manifold. Of course there's almost no draw at full throttle, but there's some flow at idle and part-throttle. But the case contents are a mix of fresh air and blow-by. I'm not sure about this but I think that emissions rules require the fresh air inlet so that blow-by gets continuously sucked through the engine and burned, rather than just accumulating and seeping into the atmosphere when the engine is stopped"

I agree in part but the only time the intake can "suck" out blow-by is when the vacuum in the intake exceeds the pressure in the crankcase. So at cruse, the vacuum will likely exceed the crankcase blow-by pressure and a "suction" will occur (suction strength will be determined by whatever amount manifold vacuum exceeds blow-by pressure). In this case a fresh air supply will be required to make-up the air vacuumed from the intake. Otherwise a vacuum would exist in the crankcase and the seals could fail "inward" not "outward as would happen with excess pressure.

At higher throttle openings manifold vacuum will be reduced until crankcase pressure will exceed vacuum and no fresh air can be "sucked" in - actually crankcase air will be "pushed" out.

Can you agree with this statement to this point?

 

I have no idea how robust the seals are against crankcase vacuum, but otherwise yes I agree with all of that. I mean, it sounds like a longer version of "...there's almost no draw at full throttle, but there's some flow at idle and part-throttle," which is what I wrote the first time around.

Dry-sump setups keep the crankcase below atmospheric pressure all the time, but I don't know how far below, or whether they use the same seals as wet-sump engines. Does anyone know if they seals changed when GM started putting dry sumps in LS7s?

 

I understand it was kind of a repeat but just trying to clarify. Next statement. Now we go to boost. Under boost we must seal the "vacuum line" to the manifold by valving to prevent pressurizing the crankcase and at the same time provide an escape for the crankcase pressure that is likely much higher at boost than non boost situations. I don't think a fresh air "make-up" will be required as the crankcase will be constantly pressurized. However, if you intend to introduce this air to be re-burned then it would have to go into the intake after the MAF because it has already been measured as intake air. If you are not an environmentalist you could simply vent this air to atmosphere. Do you agree?

 

Yep, that sounds right. My Subaru has a one-way valve on the PCV line to the intake manifold, so that line is closed during boost. There is no fresh-air pathway under boost - the head and case ports are all flowing outward. They go into the intake pipe, upstream of the compressor, which is under some vacuum (probably not much) because the compressor is sucking as hard as it can through the air filter. You could vent to atmosphere instead.

Thinking about this some more, I wonder if oil life is affected to any measurable degree on a street car that has no air flowing through the case... The oil would basically be surrounded by exhaust gas all the time, plus some raw fuel and air (from blow-by during the compression strokes). I ran my Subaru that way for years (all ports routed to the air intake) and never noticed any issues but also never had any oil analysis done back then.

 

wide open happens usually less than .1% of the time based on my data logs for your average street driver

so this 99.9x% of the time is when the pcv's 'filtration cycle' is occurring
:regulated intake manifold vacuum IS enough to not only scavenge the crankcase completely, but 'pull' clean air in to replace the foul air extracted

on wide open for n/a there can be some pcv flow still as there is light suction at the intake manifold, but for a boosted app obviously we want this path closed

on a car trying to make it a full term oil change, oil cleanliness is absolutely negatively affected by the pcv system being removed

that Subaru stuff is unnecessarily complex imo! and two cans arent needed imo, and only two hoses on a good one are (imo).

clean air in -> crankcase -> dirty air out -> GOOD catch can -> intake manifold

 

That path works for naturally aspirated setups (and it what I'll be doing in my C5), but what should the flow path be when the intake manifold pressure is higher than ambient pressure? I can't imagine a good solution for that without some complexity. But the problem might just be my imagination.