Breather and PCV discussion

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Breather and PCV discussion

This is a discussion on Breather and PCV discussion within the Veloster Performance forums, part of the Veloster Turbo Garage category; On the valve cover are a breather and PCV. The breather transfers nasty vapors into the intake and charge pipe system pre turbo while the ...

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Thread: Breather and PCV discussion

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    Breather and PCV discussion

    On the valve cover are a breather and PCV. The breather transfers nasty vapors into the intake and charge pipe system pre turbo while the PCV leads to the intake manifold. Neither one of these are good scenarios and lead to many known issues especially for our T-GDi.

    Many I see put catch cans on one or both of these lines to filter the nasty vapors out before returning to the air stream at some point. So the efficiency of the can will determine how much is going back through your motor. Since no can setup will be near 100% efficient leads me to a solution.

    Venting both lines to atmosphere or to a catch can/breather can without intake hookup..... This ensures 0 vapors will return to the intake tract to cause any cons unlike other setups. Depending on if you use cans or not to filter vapors will only determine how environmentally friendly you are.

    Every platform I've owned, and many I've worked on has had the valve cover vented to atmosphere for this reason among others. Especially an engine with a lot of blow by. My VT currently has the breather and the PCV vented to atmosphere.

    Curious of everybody's thoughts on this?
    '15 Auto VT

    PB's with slips and video:

    60' ET 2.05
    1/8 ET 8.70
    1/8 MPH 85.68 MPH
    1/4 ET 13.421
    1/4 MPH 105.57 MPH

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    How much does it effect your fuel economy (and how much does it smell)?

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    Bad.

    1. You have the job of the breather wrong. The breather is there to allow fresh air to be fed back to the CC to balance out the effect the PCV system has on creating vacuum out of the CC. The PCV works by allowing the vacuum in the IM to draw the excess vapors (blow by) rom the CC. This prevents a build of pressure in the CC by allowing it to flow to the IM and get re-burned. The problem is this can create to much vacuum in the CC which would also be bad because that would just draw more blow by into the CC. That's where the breather side kicks in by feeding fresh air back into the CC to basically balance that out. In other words you can only suck so much air out of a chamber before you create excessive vacuum. To maintain a workable level of vacuum you have to have a way for air to flow back in, it just can't be so much to eliminate all the vacuum.

    The PCV needs that vacuum effect to work efficiently so venting it to air is not good. It would be one thing if our engine and ECU were designed to function that way but they are not.

    The breather is pulling air in most of the time. The only time you'll see a burst out of the breather side is right after you let off on a hard pull. That happens much the same way the BOV blows off when you let off. There's an immediate imbalance to the vacuum so the pressure releases out the breather side to compensate.

    From the cheapest cars you can buy to the most expensive performance cars you can imagine still use this system because it works. There are variations I'm sure but the flow and concept are the same.

    You can vent the breather side to atmosphere because the breather side is just a pathway for fresh air to get in.
    The PCV needs the vacuum created by the IM to suck the bad stuff out of the CC.


    The problem that many people are having with the PCV system, which the breather is part of, is they get one or many parts of it backwards or wrong all together. Either way it has the same effect because the whole thing runs in tandem. If you get one part of it wrong you have the whole thing wrong.

    Now, can you run that way? I'm sure you could. The CC would eventually build up enough pressure where it would force pressure out but its not suppose to reach that point.
    You could also drive around for quite some time with the PCV line blocked off, I know I've done it by accident. Eventually though there will be problems that slowly get worse and by them time you see them you'll think it's being caused by something else.
    Last edited by leesrt; 08-21-2017 at 06:08 AM.
    jimlloyd40 likes this.
    2016 VT-DCT, Tech PKG (Destroyed in Wreck)
    TUNED HP/TQ: 224/258(Mustang) 242/279(Dynojet)
    Performance:SXTH 3.5" CAI, SXTH PCV OCC, Mishimoto Breather OCC, Coolant Bypass, CAT delete, Uniq Perf Strut bar, Pierce Torsion Bar, ORHP, BOV and Tork Boost Control Solenoid, HKS M40XL Plugs, 845MS Cold Pipe with HKS SSQV4, 845MS HI-FLO Catted DP Lights:DD HID 5K low beams, DD Turn as Tail, modified reverse lights, Brake light pulser, DD LED Throughout, LaminX yellow fogs

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    In the oem setup, under vacuum, the air from the intake is drawn through the breather into the valve cover, then out through the PCV to the intake manifold. Under boost, the PCV closes and vapors are going to the intake pre turbo from build up of its own crank case/valve cover pressure due to blow by. Not sure how this is incorrect.....

    Anyway, a catch can or breather can of sorts can be added to these lines to filter out any vapors. The outlet side of these cans can be vented to air so nothing goes back into the motor to cause any cons internally or routed back to a vacuum source such as intake or intake manifold to keep the environment cleaner. This may be incorrect as well.....

    To make more power you want there to be as little crank case/valve cover pressure as possible(to a certain point).

    Since the vapors from blow by exits the breather under its own pressure it can get to a point where too much pressure will build up due to insufficient flow out of the small ~3/8" breather outlet. In this case an additional breather and/or vacuum source can be placed on the breather/s to aid in the out flow and keep this power robbing valve cover/crank case pressure down. This too could be incorrect.....

    The last thing I want to do is put any information out there that's incorrect. But I'm pretty sure what I've said thus far is correct. If not I would appreciate the correct information to explain the breather and PCV functions with pros/cons and such.....
    Last edited by trdtoy; 08-22-2017 at 09:29 PM.
    '15 Auto VT

    PB's with slips and video:

    60' ET 2.05
    1/8 ET 8.70
    1/8 MPH 85.68 MPH
    1/4 ET 13.421
    1/4 MPH 105.57 MPH

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    Quote Originally Posted by trdtoy View Post
    In the oem setup, under vacuum, the vapors are drawn through the breather into the valve cover, then out through the PCV to the intake manifold. Under boost, the PCV closes and vapors are going to the intake pre turbo from build up of its own crank case/valve cover pressure due to blow by. Not sure how this is incorrect.....

    .....
    Vapors aren't drawn through the breather. The breather is there to allow fresh air into the crank case. It's passing that to the CC through the valve cover because it's convenient to do it that way. The PCV side is drawing vapor from the valve cover (CC) and letting it flow to the intake manifold under vacuum because the valve cover has will have higher pressure than the vacuum in the IM under normal driving and idle. Once you go into boost the PCV system locks up via the PCV (Valve) shutting so that the CC doesn't get pressurized by the boost pressure coming from the IM. Because it's closed up pressure does build in the CC while your under hard throttle but as soon as you release it goes back to normal. The Breather will blow out some vapor during this transition.

    The oil/gas that accumulates in a breather OCC is because of this brief blow off that happens through the breather. If you never drive hard the breather OCC would be empty all the time.

    The flow isn't going between the 2 ports on the valve cover (breather and PCV). If that were true they might as well just connect the 2 hoses together. If you look at the design the 2 outlets are on two separate compartments of the valve cover. There's an elevation difference and some chambering and the only common area is on the other end by the timing chain side.

    The PCV side is driven by the vacuum in the IM helping to pull the fumes through that path. The breather is there for the very purpose of it's name, to breath. All it's there for is to prevent to much vacuum from forming because that would have the opposite effect of what the system is doing. It's a balancing act between the two and the engine design, ECU and flow design are all designed to work together. When you change parts of it you throw the whole thing out of whack.

    Every time I hear people talk about the breather side and use the word "flow" I immediately see red flags. There is no flow, it's passive. It's just there to allow the CC to "breath" air in. The reason you want the breather side off the intake pipe is because as a by product of the design, it will blow out fumes during WOT transition to let off. It's an open port for air to flow and the PCV valve hasn't opened yet so the release has to go somewhere. If that never happened the OEM set up would be to open air as well but the average buyer doesn't want to smell that and neither do the emissions God's.

    This is why you can vent the breather to atmosphere, because it's passive. The PCV however, works off of the IM's vacuum so without that vacuum it's not working properly. That's why you can't vent it to air.

    There are race car and drag car set ups that vent the PCV to air but they use a separate pump to help extract the air rather then the IM vacuum.

    Here are pics to show how the chambers are separate, other than the one open area on the opposite end where the timing chain is.

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    Last edited by leesrt; 08-21-2017 at 10:59 AM.
    2016 VT-DCT, Tech PKG (Destroyed in Wreck)
    TUNED HP/TQ: 224/258(Mustang) 242/279(Dynojet)
    Performance:SXTH 3.5" CAI, SXTH PCV OCC, Mishimoto Breather OCC, Coolant Bypass, CAT delete, Uniq Perf Strut bar, Pierce Torsion Bar, ORHP, BOV and Tork Boost Control Solenoid, HKS M40XL Plugs, 845MS Cold Pipe with HKS SSQV4, 845MS HI-FLO Catted DP Lights:DD HID 5K low beams, DD Turn as Tail, modified reverse lights, Brake light pulser, DD LED Throughout, LaminX yellow fogs

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    Read carefully and slowly to understand the process:

    Oem setup:

    When not in boost, air flows in through the breather from the intake tube pre turbo and enters the valve cover. It then flows the length of the valve cover, makes a 180° turn and flows the length back to the PCV and continues to the intake manifold carrying vapors with it. This works off pressure differential due to more vacuum in the intake manifold than the intake pre turbo. There is very little blow by while the motor is in vacuum so less flow is needed to go out of the PCV side. This is why the PCV and it's orifice is so small in comparison to the breather side if you look at their inside diameters.

    When in boost, the PCV has almost 0 flow coming into it as it's a one way valve. I say almost 0 because it does not have a perfect seal. At this point the pressure in the crank case/valve cover from increasing blow by can only exit one place, the breather side. Between the pressure in the valve cover and the vacuum in the intake the vapors exit into the intake pre turbo.

    This system is setup for emissions only, not efficiency or power production.
    __________________________________________________ ______
    This is where having a valve cover that can flow the dirty air out sufficiently comes in. Not routing the air to air that goes through the motor is a plus and creating a vacuum in the cover is a bonus for power production.

    You mentioned drag and race cars that vent the cover more via PCV which is somewhat true(they vent the PCV or use larger breather in place of the PCV or add breathers to the cover) and one of the points I'm trying to get through to everyone. Setups like they use have pan evac in early model setups or vacuum pump in late model setups to pull/flow more air out of the valve cover, creating a vacuum within, which improves power.

    My setup venting both ports to air at all times means the pressure within the cover forces the air out just like in the oem setup, minus the small vacuum to create the extra pressure differential. The difference is that it has 2x the flow out of the cover so the pressure build up from not having the little extra vacuum assist from the intake will not really matter. At the same time I have 0 vapors going through the motor at all so the motor does not suffer from any cons from that.

    To take it one step further and add more significant power a pan evac or vacuum pump setup can be easily implemented just like on race/drag cars.

    Like I mentioned before, having can/cans setup while VTA or to a vacuum setup since not going back to intake pre turbo would just to be environmentally friendly, nothing more.....

    Hopefully this was detailed enough for most to understand.
    Incognito and TooGqForYou like this.
    '15 Auto VT

    PB's with slips and video:

    60' ET 2.05
    1/8 ET 8.70
    1/8 MPH 85.68 MPH
    1/4 ET 13.421
    1/4 MPH 105.57 MPH

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    Your second edit is correct.

    Your first post:
    the vapors are drawn through the breather into the valve cover, then out through the PCV to the intake manifold
    On your sendond post you said:
    air flows in through the breather from the intake tube pre turbo and enters the valve cover
    Your first edit has it backwards. No vapor flows into the breather into the valve cover. The only time vapors travel through the breather side is under boost because there's no where for the pressure to go due to the PCV valve being closed. Even then there's hardly any flow until you let off after WOT. The reason they connect the breather to the intake is to create a slight vacuum caused by the airflow through the intake. It's not a lot of vacuum but compared to the pressure in the CC it's enough to assist with pulling out some blow by.

    I agree that the PCV system has nothing to do with power but it does improve efficiency. If not for the PCV system a lot of those vapors would have no where to go and would just accumulate in the CC diluting the oil with fuel blow by.

    It's a simple system like I said, if one part is described wrong the whole thing is wrong.
    Last edited by leesrt; 08-21-2017 at 01:25 PM.
    2016 VT-DCT, Tech PKG (Destroyed in Wreck)
    TUNED HP/TQ: 224/258(Mustang) 242/279(Dynojet)
    Performance:SXTH 3.5" CAI, SXTH PCV OCC, Mishimoto Breather OCC, Coolant Bypass, CAT delete, Uniq Perf Strut bar, Pierce Torsion Bar, ORHP, BOV and Tork Boost Control Solenoid, HKS M40XL Plugs, 845MS Cold Pipe with HKS SSQV4, 845MS HI-FLO Catted DP Lights:DD HID 5K low beams, DD Turn as Tail, modified reverse lights, Brake light pulser, DD LED Throughout, LaminX yellow fogs

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    The valve cover is not partitioned to separate breather from PCVV, as I mentioned in the other thread with the picture I took, otherwise there would be walls with more gaskets.

    The open area where the D-CVVT rotors are located should give enough of a clue to indicate that the whole valve cover is shared. There are neither marks nor carbon deposits on the underside of the valve cover to give a hint as to a sealed partition contacting it.

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    Quote Originally Posted by leesrt View Post
    Your second edit is correct.

    Your first post:


    On your sendond post you said:


    Your first edit has it backwards. No vapor flows into the breather into the valve cover. The only time vapors travel through the breather side is under boost because there's no where for the pressure to go due to the PCV valve being closed. Even then there's hardly any flow until you let off after WOT. The reason they connect the breather to the intake is to create a slight vacuum caused by the airflow through the intake. It's not a lot of vacuum but compared to the pressure in the CC it's enough to assist with pulling out some blow by.

    I agree that the PCV system has nothing to do with power but it does improve efficiency. If not for the PCV system a lot of those vapors would have no where to go and would just accumulate in the CC diluting the oil with fuel blow by.

    It's a simple system like I said, if one part is described wrong the whole thing is wrong.
    Glad I could explain it so you understand what I was saying.

    The flow out of the cover via breather will be the same as the amount of blow by the motor produces. And yes, more will come out suddenly after sudden drop from boost to vac from the sudden pressure differential change.

    The efficiency differences and oil dilution is not going to be anything you'll notice on a VTA setup and be much improved on a vac sourced setup. And what happens in the CC has nothing to do with the oil that's important to the motor.....
    Last edited by trdtoy; 08-21-2017 at 07:16 PM.
    '15 Auto VT

    PB's with slips and video:

    60' ET 2.05
    1/8 ET 8.70
    1/8 MPH 85.68 MPH
    1/4 ET 13.421
    1/4 MPH 105.57 MPH

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    Breather side of course!!! The pcv side however i personally would NOT. The pcv system works under vaccuum which is MOST of my driving, especially long freeway haulls. It helps lower wear on rings and helps keep oil cleaner. If it was a track or race car id be all over it. Not on a daily. Its just one of those iffy things that the performance/benefits are null and the downsides are potentially worse. Im excited to see how it works out
    Flareon likes this.
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