PCV valve?

Discussion in '2011+ Mustang GT 5.0L Tech' started by dlanes, Apr 14, 2021.

  1. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    Just finished reading the article and found it very interesting how the author does recommend adding catch cans and one-way check valves in conjunction with the engine's PCV valve for FI applications.

    However, I'm not quite sure if this applies to just centrifugal type blowers or also with PD blowers as well :shrug:

    In a forced induction system, the manifold is only providing vacuum (negative pressure) at idle, low speeds, and during deceleration. At higher engine speeds and periods of boost, the system is actually under pressure. If not controlled, the increased manifold pressure will flow backwards through the valve cover into the engine, creating positive crankcase pressure. Most PVC valves are designed so that the sudden high pressure of an engine backfire closes the valve, but even the best valves become contaminated with oil and dirt so that they no longer completely block off the manifold pressure. This problem can be addressed with the use of a one-way check valve. The check valve would work with the PCV valve to limit air flow back into the crankcase. However, the gasses must still be evacuated, and this requires the use of a second evacuation channel.

    Crankcase Ventilation System, Modified for Fixed Displacement Supercharger

    This schematic illustrates the basic setup

    boosted-pcv-operation.png


    low-speed-pcv-operation.png

    basic-setup-chart.png
    The second evacuation channel is actually provided by the first part of the primary intake channel. This is only possible because that part of the system is bidirectional, allowing air to flow in both directions. When the intake manifold vacuum is high but supercharger intake vacuum is relatively low, air is pulled through the crankcase in the direction of the manifold. But when the manifold is pressurized under boost, the check valve completely closes off this part of the system. When that happens, positive crankcase pressure pushes the blow-by gasses in the opposite direction. Almost simultaneously, the air flow at the supercharger intake increases greatly. The increase in airflow results in higher vacuum at the supercharger intake, which draws in the crankcase gasses.

    Air/Oil Separators (Catch Cans)

    Catch cans are considered a requirement with any forced induction engine, including those with supercharger systems. Whenever the crankcase ventilation system is used to circulate crankcase gasses through the intake, the need to filter the air becomes even more urgent. Dirty oil vapor can coat the entire intake system, including the valves, with an insulating layer of contaminants that may also contain corrosive elements. This layer may interfere with proper cooling and heat dissipation as well as gumming up the works.

    Most importantly, oil vapor in the intake stream lowers the octane of the fuel/air mixture. This could cause engine-damaging detonation and all of the problems associated with it. Therefore, the intake of crankcase gas should always be filtered through an air/oil separator. It is important to use cans that contain oil baffles and/or some sort of filtering element. Those that require periodic draining are recommended, as the oil contained therein is contaminated and not well suited for re-use.
     
    Last edited: Apr 22, 2021
  2. eighty6gt

    eighty6gt forum member

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    check valves are only necessary in systems where you go from vacuum to boost in the pcv system/intake, ie: a turbo/etc. All of the roots-like systems don't need any of that nonsense.

    There's that thing about lowering the octane! Look at how authoritative that writing is.

    I once had a separator that allowed for oil to be returned to the crankcase, was meant for diesel engines. Because I was pulling 20+ inches of vacuum at times and almost that at idle, it just leaked and leaked. Made noise. Had to sell it.
     
    Last edited: Apr 22, 2021
    06 T-RED S/C GT likes this.
  3. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    IIRC, the Saleen VI blower has what's called a boost bypass valve which when at idle and part throttle, the engine has vacuum and pulls the bypass OPEN. Bypass OPEN equals no pressure between inlet/outlet of the SC and 0 boost. When you get on the accelerator, vacuum drops and the bypass valve shuts on it's own under spring pressure. Once closed there is no path between the outlet and inlet of the SC and you have a sealed (somewhat) outlet that builds boost.

    Anyhow, would I be correct by assuming the boost bypass valve is designed to prevent the crankcase from pressurizing once vacuum drops and the bypass valve closes when going beyond part throttle/boost?
     
  4. eighty6gt

    eighty6gt forum member

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    on the saleen blower (positive displacement) there's nothing in common with the pressure side of the system and the pcv system.

    Every pd blower I know of has a bypass or you'd have a lot more losses. So no the boost bypass valve isn't what that is for.
     
  5. Midlife Crises

    Midlife Crises Senior Member

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    The bypass used in roots type blowers is to eliminate “blower surge” and reduce puristic drag. It also helps improve fuel mileage.
     
  6. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    In that case, would you recommend removing the inline one way check valve or leave it in place in the event the PCV valve inside the driver's side cam cover should end up failing?
     
  7. Midlife Crises

    Midlife Crises Senior Member

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    The check valve you added does the same thing as the one Ford put in the cam cover. You don’t need two of them.
    Just a thought; the second check valve may offer some restriction to the airflow in that tube by acting as an orifice. Reducing the amount of airflow and the amount of oil that migrates in the airstream.
     
    06 T-RED S/C GT likes this.
  8. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    If the inline check valve may in fact offer some restriction to the airflow by acting as an orifice? then perhaps it could very well serve a meaningful purpose by reducing the amount of airflow and amount of oil that migrates in the airstream? At this point, I'll settle for all the help I can possible get, providing the second check valve doesn't create a potential risk for causing any type of damage to the engine :shrug:
    As mentioned earlier in the thread, the catch can does indeed collect oil and gets emptied at every oil change. Therefore, it continues to function as intended, despite the addition of the second check valve inline.
     
    Last edited: Apr 23, 2021
    Midlife Crises likes this.
  9. dlanes

    dlanes Junior Member

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    If anyone is interested in how my pcv setup looks this is pretty much the final setup.

    20210429_121819.jpg
     
  10. 06 T-RED S/C GT

    06 T-RED S/C GT forum member

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    Nice setup with adding the AN fittings to the valve covers including the addition of the inline check valve. Congrats :waytogo:
     
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