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Old 05-22-2009, 02:24 AM   #1
gto7419
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Default pcv setups - deleting, vta, etc

From my understanding of the pcv valve it only pulls vacuum when the manifold has - pressure. At + pressure in the manifold, the vacuum source then becomes the intake tract.

I am deleting the intake tract vacuum source. The reason being is that it sucks oil into the entire intake tract even with a catch can and can cause a knock issue if enough oil makes it into the cylinder... I have an avo air oil separater, but have come to the conclusion that its probably not going to be able to keep all the crap out of the engine and keep the oil decontaminated.

For the same logic, the pcv valve then becomes an issue as well.

Ive spoken to several people about deleting the pcv and intake vacuum systems, but Im not so enthusiastic about not having any vacuum in the crankcase at all. The crankcase needs to have vacuum for several reasons in my opinion. Preventing contamination of the oil. Allowing a better seal on the rings due to the vacuum pressure keeping them sucked against the cyl wall, and for increasing gas mileage under cruise (someone explain this)...

Ive read a lot of tech articles tonight (yes, I spent like 3 hours reading about pcv systems and crankcase vacuum) and Im debating using the exhaust system to pull vacuum from the crankcase. Ive also been thinking about using an air oil separator to prevent oil/oil vapors from being thrown out of the exhaust.

The reason Im willing to use an air oil separator/catch can on an exhaust vacuum system is because if it DOES fail to work as well as it should, it doesnt send oil into the intake tract possibly causing knock, and doesnt contaminate my oil . Frustratingly, I dont see a better option than shooting the small amounts of waste gases/oil out of the exhaust should the separator/catch can fail...

Utilizing piping connected to where the rear 02 sensor would be. I would use a very low cracking pressure ball and spring check valve to prevent the exhaust from entering the motor, and simply run that directly back to one set of breathers. Supposedly you can build around 5' of vacuum from the exhaust.

Im also debating allowing one set of breather lines from the heads to "t" with a restrictor line allowing a small mount of regulated fresh air into the crankcase while still allowing vacuum to build.

Im curious if anyone knows what kind of vacuum is pulled at the intake tract under 20lbs+ of boost to provide the crankcase with -pressure. This is what will have to be replicated as Im assuming this is the critical moment where most of the contaminants are being forced into the crankcase.

Thoughs??? Has anyone done this?
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Old 05-23-2009, 12:57 AM   #2
gto7419
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no one is running a closed or vta crankcase???
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Old 05-23-2009, 01:22 AM   #3
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Take a look at the discussion in this thread. It's about NAs, but it does give some insight to what's happening and why.
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Old 05-23-2009, 01:31 AM   #4
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I am building a VA crankcase through a breather air oil separator combo. I haven't ran it yet, I will let you know how it goes.
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Old 05-23-2009, 11:18 AM   #5
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There was a member here a couple years ago that had what you are planning. He had a vaccum gauge on the can and had the vaccum sourced the exhaust at the rear 02 sensor. It worked for him.
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Old 05-23-2009, 05:38 PM   #6
gto7419
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Quote:
Originally Posted by williaty View Post
Take a look at the discussion in this thread. It's about NAs, but it does give some insight to what's happening and why.
Well, that thread basically confirms what Ive stated - that crankcase ventilation is extremely important... However, the current crankcase ventilation system kind of stinks because it can cause detonation.

So, thats why Im not keen on simply deleting the pcv valve without replacing it with another adequate system...
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Old 05-23-2009, 05:39 PM   #7
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Quote:
Originally Posted by scby rex View Post
There was a member here a couple years ago that had what you are planning. He had a vaccum gauge on the can and had the vaccum sourced the exhaust at the rear 02 sensor. It worked for him.
remember his username? ive searched most of nasioc...
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Old 05-23-2009, 06:31 PM   #8
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i get where your coming from, but your over thinking it. the little bit of vacuum that you can get in the crankcase wont do anything useful to aid in ring seal. combustion pressure does that. i have no pcv and run vta thru a catch can. sure the oil gets dirty, but its not from the crankcase ventilation, its from the loose pistons in my built block. also, the lack of a pcv valve wont cause detonation. venting to the turbo inlet and letting the motor suck down crankcase fumes will. with vta, its impossible.
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Old 05-23-2009, 06:43 PM   #9
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Just run everything into a catch can that is set up correctly. When I say everything ( I mean both head breathers-Crank breather and the line to the gas tank ) I use a greddy knock off type can that is modded and custom baffeled ...... it works flawlessly. PM me if you want more info
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Old 05-23-2009, 08:39 PM   #10
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Ive done that ^^ The catch cans dont work flawlessly - I dont want anything being recirc'd back into the engine...
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Old 05-23-2009, 09:35 PM   #11
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Install a dry sump and have it scavenge the crank case. It's cheap and easy honest
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Old 05-23-2009, 09:49 PM   #12
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Quote:
Originally Posted by mick_the_ginge View Post
Install a dry sump and have it scavenge the crank case. It's cheap and easy honest
I think I'd rather the motor blow up - twice - then have to deal with a dry sump!

Ive seen your setup and its pretty damn nice, but I do not have that kind of cash - and I need the trunk as its a daily and my hauler...
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Old 05-24-2009, 08:05 AM   #13
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Quote:
Originally Posted by gto7419 View Post
Ive done that ^^ The catch cans dont work flawlessly - I dont want anything being recirc'd back into the engine...
Um the trick is to not re-serk anything into the motor .....let it go out to the atmosphere.....the baffeling creats slight back presure
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Old 05-24-2009, 11:47 AM   #14
gto7419
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You dont want back pressure - you want vacuum... I dont want the crap forced out - I want it pulled out...
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Old 05-24-2009, 12:28 PM   #15
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So, how are you going to source vacuum then? Isn't that the main question? I'm wondering how much of a pump I'd need to vacuum down the crankcase. Would an inline fan do it? Something like the fans used for brake cooling? I'm just not clear on the volume necessary. Would a single stage dry sump pump setup just to suck air do the trick?

If you think about the PCV operation when in vaccum, it's really not pulling much of a volume of air through the valve. If I was to attach a permanent vacuum source to the PCV valve, independent of manifold pressure. and vent the breather hoses to atmosphere though a filter, would that be sufficient?
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Old 05-24-2009, 01:45 PM   #16
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Quote:
Originally Posted by MasterKwan View Post
So, how are you going to source vacuum then? Isn't that the main question? I'm wondering how much of a pump I'd need to vacuum down the crankcase. Would an inline fan do it? Something like the fans used for brake cooling? I'm just not clear on the volume necessary. Would a single stage dry sump pump setup just to suck air do the trick?

If you think about the PCV operation when in vaccum, it's really not pulling much of a volume of air through the valve. If I was to attach a permanent vacuum source to the PCV valve, independent of manifold pressure. and vent the breather hoses to atmosphere though a filter, would that be sufficient?
Im not clear on the volume needed either... Someone want to put a vacuum gauge on their pcv line?

Yes and no - the pcv valve only pulls vacuum when theres vacuum in the manifold... When theres + pressure in the manifold the pcv valve closes and the vacuum for the crankcase is then pulled from the intake tract. So just having the pcv valve doesnt work. You need a vacuum source for both manifold conditions of boost and vacuum.

So basically, I need a constant source of vacuum - which I think I can use the exhaust for... The question is, how much vacuum is needed, and, can I put a pump on the line to assist?
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Old 05-24-2009, 02:01 PM   #17
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Wittmer25 uses a Mann-provent it drains to the pan. Lingfelter was using it on the turbo corvettes. It's really for big diesels though and the o-rings swell up after awhile so you gotta get new orings for gas instead of diesel motors. It needs 1/2 breather lines and a extra pcv that will go in the line to the intake infront of the turbo to stop the oil mist back into the intake. You might just add the extra pcv and maybe it will solve your problems. You could also extend the line and that might help.
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Old 05-24-2009, 02:05 PM   #18
gto7419
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Originally, I thought I would want to drain to the pan too, but whatever gets blown or sucked out - is contaminated and I dont want to return it to the oil pan...
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Old 05-24-2009, 03:31 PM   #19
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If you do not want to recirc anything, then there is a contraption made that may interest you.

http://forums.nasioc.com/forums/show....php?t=1743381
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Old 05-24-2009, 03:55 PM   #20
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Quote:
Originally Posted by CKxx View Post
If you do not want to recirc anything, then there is a contraption made that may interest you.

http://forums.nasioc.com/forums/show....php?t=1743381
I'd be hesitant about using one of those. If you get a blockage at your exhaust tip (back into a snow bank, 3 year old sticks a potato into your exhaust tip, etc.), you could blow all of the seals out of your motor in short order. Plus, the exhaust gasses coming out of the engine are pressurized, if you have any kind of restriction after your ghetto 'exhaust draft tube', you will be pressurizing your crank case almost all the time. Food for thought.
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Old 05-24-2009, 04:13 PM   #21
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Given the application I figured he would be using a large sewer pipe exhaust and not be driving in the snow!
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Old 05-24-2009, 04:29 PM   #22
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The only things that have been tried are a drysump/scavange pump and catchcans. Which you have stated that you don't wish to do either.

Time to buck-up and try something, report results for the next guy.


Personally, I don't like the exhuast idea. Bad for a street car, and I don't think it will get by most track inspectors unless there is a failsafe for excessive leakage/spillage in case of an accident/rollover/system failure.
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Old 05-24-2009, 05:36 PM   #23
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Quote:
Yes and no - the pcv valve only pulls vacuum when theres vacuum in the manifold... When theres + pressure in the manifold the pcv valve closes and the vacuum for the crankcase is then pulled from the intake tract. So just having the pcv valve doesnt work. You need a vacuum source for both manifold conditions of boost and vacuum.
If you have permanent source of vacuum, electric pump or something that'll pull 20" mercury and have sufficient volume, you don't need the hose to the inlet that's there now. As you point out, it's only used when the manifold is in positive pressure so, the PCV is shut off. If your source of vacuum is a pump then you disconnect and plug the hose to the inlet and just use the PCV. You probably don't need the PCV valve at all then and can simply plug up the vacuum line under the throttle body and pull the fumes directly out of the crank case.

In honda's at high RPM's the vent tubes switch from inlet to outlet, not intentionally but, because there isn't enough vacuum in the CC at that point to scavange the fumes out. The pumping action of the pistons pushes air and oil out of the inlet. Wonder if suby's have the same issue. The venting of an STI is quite different than a WRX. There's a balance tube across the back of the motor which seems to be there to equalize pressure between the heads and the crank case. Maybe it's intended to prevent pressure buildup in the heads which prevents oil from draining back. Certainly my STI motor consumes less oil on track than my WRX motor did. I wonder if that additional venting helps prevent oil being pushed into the inlet through the vent?
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Old 05-24-2009, 07:02 PM   #24
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Was going to post these earlier but im out of town, but I just realized they are on my photobucket and can access the pics on this comp. But what about a catchcan like this? 2 - 1/2" ports for each valve cover and 1 - 3/4" port to eliminate the pcv. Baffled up top, bung welded on the bottom for a brass draincock and either vta via a filer on top or a recirc tube on top to draw vacuum.



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Old 05-24-2009, 07:58 PM   #25
gto7419
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Quote:
Originally Posted by Chi_San View Post
I'd be hesitant about using one of those. If you get a blockage at your exhaust tip (back into a snow bank, 3 year old sticks a potato into your exhaust tip, etc.), you could blow all of the seals out of your motor in short order. Plus, the exhaust gasses coming out of the engine are pressurized, if you have any kind of restriction after your ghetto 'exhaust draft tube', you will be pressurizing your crank case almost all the time. Food for thought.
Not with a one way check valve As well, I can get a relief valve that will let pressure be relieved if it goes over a certain pressure...

cx - thats exactly what I was thinking about

Rally - if used inconjunction with a catch can, I wont be blowing oil out of the tail pipe...

MK - I think the additional venting DEFINATELY helps...

Im thinking about using the exhaust source for vacuum with a one way check valve - When the motor is finished Ill do some tests and see what I can pull for vacuum out of the rear 02 hole...

If I dont get the kind of vacuum Im looking for, I might look at an electric vacuum pump....

Either way, Im going to need relief valves that down allow more than x amount vacuum and x valves that prevent pressure build up...

Murphy - the problem isnt with the catch cans, its that I want to pull vacuum, but not from the intake tract...

Last edited by gto7419; 05-24-2009 at 08:06 PM.
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