Crank case venting

[GVR-4]

I've been chewing on this for a while but thought I would get some input from you guys. Here's the question: Does NOT plumbing the valve cover vent back into the intake tract affect tuning? The thing is, that blowby that escaped past the rings (when under boost) ends up in the crank case and has been metered by the MAS. I would think that venting the blowby to the atmosphere would result in a rich condition since the ECU thinks that air is present (via recirculation) when it is really not.

Discuss...

 

[mitsuturbo]

I believe the majority of blowby is comprised of gasses that have already seen the combustion process and therefore it is of little or no consequence after the fact. I'd think it'd be more likely to dilute/contaminate the fresh air you have coming into the intake manifold. Even engines out of jdm cars without EGR have a lot of crap built up in the intake manifold. I'd assume this is from PCV, and it usually looks like a caked on oil/carbon mixture. Carbon is a byproduct of combustion, yes? Oil is in the crankcase, and atomizes in the air inside the block, carries carbon into the intake manifold.. and then you get "gunk".

This is my theory. I'd like to see some sort of affirmation, criticism, or rejection of this theory. /ubbthreads/images/graemlins/dunno.gif

 

[mikus]

VCV vents air that slipped past valve seals, PCV vents air that slipped past rings. Both are loss of metered air... I'd agree with above that it's for the most part "past combustion" and has a marginal effect on your AFR.

That's just my opinion from reading 3294072349 threads on it though, i do not have and haven't seen objective data on how much that metered air loss really matters. I'd guess if it was really a big deal for AFR, we'd see a lot more data/examples and a lot less theory on the topic.

 

[GVR-4]

Thanks for the thoughtful responses, guys. I'd like to hear what Jeff O. thinks too.

 

[mitsuturbo]

OK. I'll bite. I'm curious. What is VCV?

 

[4thStroke]

Valve Cover Vapor?

In this context, it makes sense to me.

/ubbthreads/images/graemlins/dunno.gif

 

[The_Big_Weave]

I heard that if it is not recirculated into the intake that you can get some oil leaks you never had before. Something about pulling the extra pressure out of the crank case.

 

[mitsuturbo]

I believe the guys making a ton of power are running crankcase evacuation to the exhaust.
Here's a demonstration.

It looks like the exhaust slashcut (bernoulli effect) crankcase evacuation system seems to work pretty well, but there's no way it'd ever be emissions compliant. /ubbthreads/images/graemlins/smile.gif

 

[ktmrider]

Quoting 4thStroke:
Valve Cover Vapor?

In this context, it makes sense to me.

/ubbthreads/images/graemlins/dunno.gif

Valve Cover Vent. You can see where the baffling inside helps vent vapors from different area of the head than the PCV port.
I can tell you this much, when I had the bad Fram-inator PCV the car ran quite rich among other things ( popping the dipstick under sustained boost the worst ). She runs a ton better with the OEM PCV and VCV ventilation hookups plus I have not noted any significant oil buildup in the intake tract ( running 17psi of boost on average ).
IMO a catchcan is only "needed" when running big boost ( 25psi and over ). Outside of that they really only compensate for poor engine condition.
Last, my emission friendly side says don't give the EPA and tree huggers more ammo to put CARB-like restrictions on the entire country. Venting to atmosphere not only causes poor engine ventilation ( not enough pressure difference to extract the vapors entirely ) it dumps some fugly stuff into the air we breathe.
Ok, the soapbox is put away.... /ubbthreads/images/graemlins/grin.gif

 

[mikus]

The gases being vented are corrosive, and the vacuum in crankcase improves mpg...

You'll find someone running OK with just about any configuration (except any blocking/closing like a breather filter directly on it)

#1886 runs VCV to atmosphere and PCV to intake with no problems, I often hear not to "cross the streams" vacuum and atmos. - but it was tuned with this configuration.

#39 had problems when I went from OEM setup to vent to atmosphere on it's older stock motor - it popped dipstick and had condensation issues.. but VTA does work for many.

 

Quoting GVR-4:
I'd like to hear what Jeff O. thinks too.



Mikus has Jeff O's #1886, so you know what I think. /ubbthreads/images/graemlins/wink.gif

 

[3rdstrikedsm]

Big turbo supra guys have been doing this for years with great success.

 

Its true, Travis Deems' "FatDrift" RB25 240sx has this same plumbing, but with slick -AN fittings.

 

The vcv that people have been talking about is still a crankcase vent. this about this. how do you think oil flows so easily from valve cover to oil pan. thats because there are enormous ports. any pressure you have in the crankcase there will be equal
pressure in the valve cover. hooking the hose back upto the intake allows for marginal amount vacuum to be applied. one of the reasons they put the crank vent at this top of the motor is to allow the oil vapor to seperate from the air condensate and travel back to the oil pan. (mercedes 4 bangers actually have air oil seperators that make the crank case air travel through a long narrow passage and pulls just air out the top). if you were super worried about it you could easily rig something like that up. and to those people who noted the excessive amount of oil and garbage in the intake manifold, this is because the oil vapor isnt seperating from tha air until it reaches your intake. Its quite common on merc 4 bangers with bad air oil seperators to end up needing new a new intercooler, and mas. sucks real good. hope this answered your question.

 

[CutlassJim]

It didn't.

 

Travis Deems' Crankcase Vent setup.

 

I doubt it will have any effect on your af ratio at all.

 

Here you go for a sweet breather setup. 110,000 mile engine. Plenty of blow-by, and not a single drop of oil in the intake tract now. Can drains back into block.