Mustang Parts and Tech
Engine Breathers and Deleting the Stock PCV System

Information on running a dual PCV valve system

Breather systems with a larger 5/8" line

A little background:

Previously with the stock one valve PCV system, I would drain the separator about every 500 - 750 miles and wipe the
excess off the bottom of my throttle body.  With the one PCV and no separator, there was enough oil pulled through the
system to puddle in the upper intake and occasionally run down my intake tube toward the MAF meter.  I have baffles
installed in all of the stock locations with stock valve covers.  My Holley lower intake has the baffle installed that came
with product and the screen mesh under the PCV valve is in place.  Oil consumption through the PCV system has varied
widely on the intakes I've installed with no other changes made to the engine during the swap (GT-40, Vortech/Saleen,
Holley).   Holley being the worst offender with the Vortech/Saleen closely following.  Oil consumption from the GT-40 was
the closest to a stock intake PCV system.  The dual PCV valve and breather system write ups are based on my current
set-up.  That includes a built 347 with HCI and a Vortech supercharger with approximately 12 pounds of boost.  There
are about 70k miles on the short block, and I would feel safe to say it's in good condition and no different than your
average Mustang in the real world.

Deleting the PCV System:

You can't run a PCV system in conjunction with a breather or you will create your own vacuum leak.  The engine would
be drawing in air from the PCV valve which is now open to the atmosphere at the breather and unmeasured air would
be entering the intake.  I have seen a breather used in a PCV system, but there was a one way valve installed in the
breather that only allowed excess internal engine pressures to vent outward to the atmosphere.

There are only a few things to do to delete the PCV system.

  1. Remove the vacuum line that runs from the top of the throttle body to the passenger side valve cover at the oil fill
  2. Place a vacuum cap over the two hose nipples you just exposed by removing the hose.
  3. Remove the vacuum line from the upper intake that leads to the PCV valve and cap the exposed hose nipple(S).
  4. Remove the PCV valve from the rear of the lower intake but leave the stock grommet in place.

After removing the lines and capping off the hose nipples, you still need to allow the engine to breathe because you are
no longer pulling fresh air through the engine with engine vacuum.  If you merely cap off all the openings, the built up
engine pressure will find its way out through your engine seals.  By deleting the PCV system, you may also find that you
need to increase your engine idle RPM slightly.  Each engine is different and it will depend on your application.  The
following are several of the methods I've used to finish off the breather system.

Method 1   (Basic Breather System):

If I had to guess, this is the most common method found.  The oil cap on the passenger side valve cover is removed and
a screw-in breather is installed.  Some people have just capped off the rear PCV valve location and left it at that.  
Personally, I believe there needs to be a little more venting.  The addition to this method would be to place a small
breather at the old PCV valve location.  The smaller breather can be found in the 'ricer' section of your local auto parts
store and it will typically have a 3/8" hose end.  Depending on your application (Naturally Aspirated or Supercharged),
the speed at which oil will eventually find itself dripping off the screw in breather onto the passenger valve cover will
vary.  If this is not desirable you may consider upgrading to a higher Method below.

To make the breather for the PCV valve location follow along.  

Part 1:  The stock PCV valve grommet that fits into the lower intake has an approximately inner
diameter of 5/8".  It would be difficult to find a fitting that would allow you to mate a breather
to this location, why make it hard.  Take a stock PCV valve and grind / cut off the bottom
lip.  The inner spring and plunger are easily removed from the PCV valve shell and you now
have the perfect fitting.  Place the gutted PCV valve into the stock grommet.

Part 2:  The smaller top of the PCV valve mates to a 3/8" hose.  Oil vapors and mist will enter
the PCV valve shell with this configuration as engine pressure pushes outward.  So, create a
little space before you mount the breather right on top of the PCV.  Add about a 4" line of 3/8"
vacuum hose between the PCV and the breather.  This will help prevent oil from dripping on the rear of the engine and
allow any build up in the hose to drain back into the engine when it's shut down.  You will need to purchase a 3/8" hose
barb to hose barb fitting to mate the 'ricer' breather (it has a female end) to the 4" x 3/8" hose unless you do mount it
directly to the PCV.  Method 1 is complete.

Method 2   (Breather System With A Remote Breather):

This system is similar to Method 1, however, it provides for a remote breather
that is no longer on the top of the engine.  This will help keep oil from dripping
on the valve cover, and the extra length of the vacuum hose
appears to allow
for more vapor / condensation to evaporate before it even gets to the remote
breather element.  This method will probably work great in a mild naturally
aspirated engine.  You will continue to use the modified PCV valve shell as
created in Method 1.

Remote breathers are not very expensive and can be found for about $30 on
up.  I'm currently using a Moroso Dry Sump Breather Tank (MOR-85470) that I
purchased from Summit Racing for $70.  This breather tank works as both an
oil/air separator and a remote breather tank.  I purchased the tank in 2005,
but when I pull up this model number today on Summit Racing, the picture of
the tank is similar and the fitting sizes are correct, but my mounting bracket
is styled like the MOR-85460 (lower photo).  So if my pictures don't match the
item, it's only the mounting bracket thats different.  You could still use the 85460
and purchase an AN to hose barb fitting to match your needs.

The idea here is to combine the two breather elements (passenger valve cover breather and the PCV
valve breather) using a 'T' fitting, 3/8" hose, and the remote breather.  You'll first have to find a suitable
location in the engine bay to mount the remote breather.  If you still have most of the engine accessories,
I found that mine will fit on the front of the passenger side frame rail directly under the radiator hose.  

    Remote Breather Installation:  Instead of drilling holes into my frame rail to mount the
    breather I bent an angle bracket out of aluminum.  The bracket is held with the two bolts
    that hold the fuel vapor canister and angles upward into the engine bay.  I pushed the
    fuel vapor canister forward and reversed it to where it sits on the outside of the frame
    rail.  It's only held in place by one bolt which I drilled and tapped new, and I cut a small
    portion out of the plastic inner fender to allow both items to remain in place.  The unit
    clears the Vortech head unit and brackets, alternator, smog pump, belts, A/C lines, fan
    shroud, and radiator hose.  My Hiding Engine Wires page shows the Vortech method to
    mount the vapor canister.  I've simply reversed the entire unit.   If you have more of a
    race oriented vehicle / engine bay, mounting the tank somewhere is probably not as

    Vacuum Hose Configuration:  Once the remote breather is mounted, hooking up the
    vacuum lines is fairly straight forward.  You'll need approximately 5-6' of 3/8" vacuum line
    and a 3/8" 'T' fitting.  The easiest way is to remove the 'ricer' breather located above the
    PCV valve shell and attach one end of your new 3/8" line.  If you have a screw in
    breather, remove the screw in breather and replace it with the stock cap.  (You could
    leave the screw in breather in place for extra venting but it defeats the purpose of the
    remote breather).  Also remove the vacuum cap on the hose nipple on the oil fill tube (if
    previously installed).  Place a new 3/8" line on the oil fill tube hose nipple and 'T' that line
    into the 3/8" line from the PCV valve shell.  Add the third 3/8" line off the last end of your
    'T' and attach it to the remote breather.  That completes running a remote breather
    system using a 3/8" line.

Continue to page 2;    Method 3 (Breather System With A Remote Breather and 5/8" Line)