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How the PCV system works and why it is beneficial.

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  • How the PCV system works and why it is beneficial.

    Lets get this discussion started with a description of the PCV system, courtesy of Wikipedia (Full Article).

    Originally posted by wikipedia
    A crankcase ventilation system is a way for gases to escape in a controlled manner from the crankcase of an internal combustion engine. A common type of such system is a positive crankcase ventilation (PCV) system, the heart of which is a PCV valve—a variable-restriction valve that can react to changing pressure values and intermittently allow the passage of the gases to their intended destination (which nowadays is the engine's intake stream).
    Internal combustion inevitably involves a small but continual amount of blow-by, which is when some of the gases from the combustion leak past the piston rings (that is, blow by them) to end up inside the crankcase. The gases could be vented through a simple hole or tube directly to the atmosphere, or they could "find their own way out" past baffles or past the oil seals of shafts or the gaskets of bolted joints. This is not a problem from a mechanical engineering viewpoint alone; but from other viewpoints, such as cleanliness for the user and environmental protection, such simple ventilation methods are not enough; escape of oil and gases must be prevented via a closed system that routes the escaping gases to the engine's intake stream and allows fresh air to come in.
    Ok, lets get on with the technical discussion - How the PCV system works and why it is beneficial.
    89 Mustang : Future 60V6 Power
    Follow the build ->

  • #2
    The best setup would filter the oil and blow by gases from being ingested by the motor. The EGR is a control leak of exhaust gases into the intake, which when mixed with oil vapor create a heavier, sticky carbon deposit that will decrease performance and efficiency. The PCV system that relies on engine vacuum also creates a real concern for the fresh intake charge, as the oil vapor will effectively reduce the octane of the fuel mixing with the air. If you are experiencing knock with what seems like very little spark advance, this could be your issue.

    The benefits to using vacuum on the crankcase are worth the effort, with less resistance underneath the pistons for extra power output at the crank, improved ring seal for less blow by, less chance for oil seals being compromised from crankcase pressure, and all of this resulting in better MPG as well.

    An electric or mechanical pump that pulls higher vacuum on the crankcase is worth more power than one that relies on engine vacuum.


    • #3
      On my Camaro I use an exhaust slashcut evacuation. It works VERY well. Stock PCV valve on one valve cover and the slashcut on the other valvecover. (instead of having it go through the turbo/piping/intercooler.)
      11.92 @ 122 MPH 3400 91 Cavalier Z24 Intercooled S/C. -totalled-
      10.56 @ 130 MPH 3900 LZ9 87 IROC Z28 Intercooled GT4088 Turbo


      • #4
        I found a 2 part video on youtube that expands on what Ben said and has a visual explanation using a Toyota engine in a Lotus application. The first part goes into the details of the stock setup which should be similar to most street cars and the second part explains setups used in high performance racing applications. It is very easy to follow for those more visually oriented.

        I have seen a number of filters around on ebay that are aluminum with cooling fins and have a chamber to them that help slow down and cool the crankcase gasses so the filter can remove the bulk of the oil and large particles from the air before it goes to the intake. Many have the same designs to them and probably a common filter element.

        One point mentioned in the video is how the standard PCV system in a street car will take metered air from in front of the throttle plate and mixes with the crankcase gasses to return to the airstream behind the throttle plate via manifold vacuum. It should be easy to see how a leak from this system would cause problems with engine performance as some of the air read by the MAF would not be making it to the cylinders.

        Another thing I noticed was some of the European cars have a PCV valve and oil separator with very large diaphragm. Many of them seem to have hose barbs so they could be used on any engine. I would imagine the larger diaphragm engages and disengages at very low air pressures and ones with a built in oil separator would be a cheap and easy upgrade to add to any car.
        Attached Files


        • #5
          BAH! :P

          I'll do what mars is doing but that's as far as I'm going!!!
          sigpicHow to make High performance Emissions:
          A "true" High flow converter, straight pipe.
          Low/No flow EGR valve, block off plate.
          Carbon canister and purge valve mod, place in large 30 Gallon can, cover, and place curbside, the city will do the rest.
          PCV valve and vent tube, reroute to exhaust to dump where it belongs, on the ground. Or add breathers and let it all free.