How-to's => Resources => Topic started by: onederful100 on April 03, 2009, 09:16:23 AM

Title: PCV and breathers
Post by: onederful100 on April 03, 2009, 09:16:23 AM
i'll post this here bc sometimes it takes me a while to look for it when someone wants pcv's and breathers explained.
Title: Re: PCV and breathers
Post by: BJs03GT on April 03, 2009, 09:37:00 AM
gav your linky no worky, or might be cause i using my phone
Title: Re: PCV and breathers
Post by: BJs03GT on April 03, 2009, 10:12:03 AM
n/m it does work, it was cause i was using my phone and it no read that kine stuff.
Title: Re: PCV and breathers
Post by: onederful100 on April 03, 2009, 10:36:21 AM
i just clicked it and it didnt work.  heres the article just in case.

PCV Bypass
Theres a right and a wrong way to bypass your PCV (Positive Crankcase Ventilation) system. Before we
show you the how to, lets first understand the function of the PCV system. The PCV system is intended to
relieve the crankcase of any positive pressure by allowing it to vent through the free flow of air, either into or
out of the crankcase. Prior to advent of emissions, the crankcase was just vented through a breather on the
valve covers or intake manifold to the environment. Emissions requirements necessitated a “cleaner” way to
vent the crankcase to prevent the hot oil laden vapors from damaging air quality. That led to the inclusion of
today’s modern PCV systems. Current PCV systems are still pretty simple, consisting of an air inlet, a valve,
and an outlet. The air inlet (the vent tube) supplies filtered and metered airflow into the crankcase. The PCV
valve, which when opened by either internal intake manifold vacuum or positive crankcase pressure, vents
into the intake manifold, allowing the now oil contaminated but otherwise filtered and metered crankcase ventilation
airflow to be consumed by normal combustion processes.
Its important to note 2 significant issues:
1) The crankcase ventilation airflow is metered since the vent tube is located after the MAF. Because the airflow
is metered, it must make it into the intake manifold to assure that the air/fuel ratio is correct. Therefore, if
we bypass the PCV system, it must done in such way that no unmetered air can reach the intake manifold, for
if it does, the air/fuel ratio will be adversely affected. Similarly, any metered airflow in the PCV system must
make it all the way to the intake for the same reason. What this means is, if you bypass the PCV system, it
must be bypassed completely, both the inlet and the outlet air transfer paths must be blocked. You just can’t
block off one and not the other.
2) The PCV valve is intended to be opened by intake manifold vacuum (negative pressure), but can also be
opened by positive crankcase pressure. Therefore, whenever vacuum is present in the intake manifold, the
crankcase pressure will vent into the manifold and the ventilation air is “drawn” into the intake manifold
through the PCV valve all the way through the crankcase, vent tube, MAF, and air filter. Furthermore, when
positive crankcase pressure is present, it will be vented through the PCV valve into the intake manifold.
There’s no problem at all under most circumstances, but there can be very significant issues in certain applications,
especially if substantial cylinder blowby is present, if the PCV system is overly effective, or if supercharged.
Who needs to bypass the PCV system? In most applications, the PCV system works just fine, but certain hipo
applications may run better with the PCV system bypassed, even though your car will no longer be emissions
legal. In that case, the decision is yours, bypass the PCV or remain emissions legal? High compression
engines setup with low tension oil control rings are a real good application for PCV bypass. Engines with
poor ring seal and substantial blowby will also benefit because the incoming air charge will not be oil laden,
which effectively lowers the octane of the air/fuel mixture and increases susceptibility to pre-ignition, detonation,
etc. The 99-up models seem to have acute issues with overly effective PCV systems, just about every
intake manifold we’ve seen has been thoroughly soaked with oil. In fact, Ford issued a service bulletin for
valve cover replacement reportedly using revised baffling to minimize oil contamination of the air charge.
However, we think that has been ineffective. More on that later.
OK, lets do it.
94-98 3.8L V6 Mustang using dual breathers: Remove the air inlet tube that runs from the convoluted intake
tube to the driver’s side valve cover. Plug or cap the hole left in the intake tube. Insert a small .75” K&N
breather in the hole left in the valve cover. Remove the upper intake manifold, the PCV valve, and the line to
the port underneath the plenum of the upper intake. Insert another small breather into the hole left in the passenger
side valve cover by the removal of the PCV valve, and cap off the port in the intake manifold. Extend
the evap cannister purge vent line past the solenoid to a tee that you’ll instal into the primary vacuum line at
the upper intake manifold. The PCV system is now completely removed and blocked off such that the air/fuel
ratio is unaffected.
99-up 3.8L V6 Mustang using dual breathers: Remove the air inlet tube that runs from the convoluted intake
tube to the passenger side valve cover. Plug or cap the hole left in the intake tube. Insert a small breather
into the hole in the valve cover. Remove the PCV valve and line from the driver’s side valve cover. Cap the
fitting in the upper intake manifold and insert another small breather into hole left in the valve cover. Extend
the evap cannister purge vent line past the solenoid to a tee that you’ll install into the primary vacuum line at
the upper intake manifold.
94-up single breather: Remove the air inlet tube that runs from the convoluted intake tube to the valve cover
vent. Plug or cap the hole left in the intake tube. Cut off the tube an inch or so from the plastic valve cover
fitting, and cap off the valve cover fitting. Remove the oil filler cap and install a screw-on K&N breather. Disconnect
the line running from the PCV valve to the intake manifold at the PCV valve. Cap the PCV valve outlet
and plug the line. Leave the evap cannister purge line connected to the PCV valve line as it is.
You have a 99-up model with overly effective PCV system that contaminates the intake manifolds and impairs
performance? If you intend to leave the PCV system intact, here’s a potential quick fix that you may try. Remove
the PCV valve cover. Enlarge the drain back hole in the baffle. Stuff the baffle with coarse stainless
steel wool but don’t pack it too tightly. The steel wool should help by “straining” the oil from the air flow.
Lets talk about supercharged or turbo applications. We think the dual vent system is the way to go in any
high boost or blowby application because the general flow requirements through the PCV system are restricted
by the small size of the lines and the small aperatures of the vent and PCV valve. This is especially
critical on the 99-up models which already have PCV systems which may be seriously diluting the air/fuel octane
with oil vapor.
A word of caution regarding the use of one-way valves in the PCV system of supercharged applications. We
don’t recommend it. Here’s why. Lets say you have a problem with blowby that deposits oil into the compressor
inlet from the vent line, pretty common problem. Stop and remember how and why the PCV system
works. Engine vacuum (negative pressure) opens the PCV valve, and draws ventilation supply flow, i.e., metered
air, through the engine and into the intake manifold. Now, in boosted applications, the intake manifold
will be under vacuum only at very low rpms. Most of the time, the intake manifold will actually be under boost
and therefore will be under positive pressure. Therein lies the problem. Even though the PCV will open under
positive crankcase pressure, that positive pressure created in the crankcase by blowby is acting against a
greater or equal positive pressure in the intake manifold. When both sides of the PCV valve are at the same
pressure (pressure is acting on opposite sides of the diaphragm), there will be zero flow because the valve
can’t open. That means that you’ve now positively pressurized the crankcase by blowby. Now, the PCV system
has to act in reverse. The flow and pressure will be vented the wrong way through the vent line over to
the supercharger inlet. This is the point where one theory recommends the use of a one way valve. The theory
is to orient the valve to only allow flow into the crankcase, but not out from the crankcase. While that
might be acceptable on a really tight engine, the fact is that most supercharged engines run a fair amount of
blowby. The problem is, with the one-way valve installed, there is no path to vent the blowby, which is going
to pressurize the crankcase since there can now be no path to relieve the positive pressure except around
seals and gaskets, which will cause them to leak. Also, remember that positive cranckase pressure also
hurts performance.
The drawback to venting an engine’s blowby is that the breathers will eventually become oily and start to drip.
The answer is not pretty but it is effective. Periodically remove the breathers, wash them in solvent or K&N
filter cleaner to remove the oil, reinstal them, and wipe off your valvecovers.
Title: Re: PCV and breathers
Post by: onederful100 on April 07, 2009, 03:24:11 PM
this is the breather that i have on the oil filler cap

heres one for 86-04

my breathers on the valve covers are K&N, can get at Rons or order from jegs or summit if Rons no more in stock.
Title: Re: PCV and breathers
Post by: mrunclesocio on April 09, 2009, 07:54:00 AM
Thank you Gavin...I got to go back and read it better which means like at least 3 more times...
That is some good info to try to remember.
Title: Re: PCV and breathers
Post by: onederful100 on October 06, 2009, 08:30:26 AM
just thought i would mention.  i was getting blowby out the passenger side breather.  i have since switched oil to 5w30 mobil 1 from 5w20 mobil 1 and keep the breathers clean, and now i have no blowby.
Title: Re: PCV and breathers
Post by: humbleLX on November 21, 2009, 02:19:31 PM
Putting a Stop to Oil Consumption through the PCV Valve

Background Info on the PCV System
The PCV is an emissions device that allows the pressure and corrosive gasses in the crankcase to vent, without venting these harmful gasses to the environment. The directional valve is in place to prevent a backfire from spreading to the crankcase. In the event of a backfire into the intake manifold, the PCV is supposed to seal shut, preventing the flame front from traveling into the crankcase. Without this directional valve in place (and fully functional) a backfire could also cause a crankcase explosion.
All motors will experience some degree of Blowby. Even a freshly rebuilt motor can experience between 5-10% Blowby, as checked with a Leakdown test. (Blowby is not the only source of crankcase pressure however. Due to the reciprocation of the pistons there will be a build up of pressure due to the air not being able to flow as fast as the pistons are moving in the higher RPMs) Blowby of combustion gasses introduces fuel and other combustion by products into the crankcase. Raw fuel, moisture, and various acidic materials will all contaminate the engine oil. Moisture can also enter the crankcase due to condensation overnight.
The good news is that most of these contaminants are highly volatile, meaning they will vaporize at relatively low temps; around 200F. Once these contaminants and moisture have volatized though, they must be purged from the crankcase. This is where a crankcase ventilation system comes in.
In the old days the crankcase was vented to the atmosphere via a hose that ran under the car or into the exhaust. The downside to this is that these volatile materials were being introduced to the atmosphere, increasing environmental damage. Now a Positive Crankcase Ventilation system is in use. In a positive venting system the crankcase contaminants are purged into the intake manifold so that they can be burned in the normal combustion process. This is very effective at reducing the amount of unburned HCs that are released to the atmosphere.

Troubleshooting Your Oil Control Issues
The first step is to find out where the oil is coming from.
Pull the Throttle Body/Valve Cover hose from the TB. If it is wet with oil then this is an entry point. The normal causes of this are excess Blowby (which needs to be ruled out with a compression test), or the VC baffle has been removed for rocker clearance. Just looking down the oil filler neck should reveal if the baffle is in place. If you see rockers, then it is time to get creative and fabricate a baffle. If there is no baffle but the TB/VC hose is bone dry then you may be able to get away without using a baffle.
Next pull the PCV hose. Again if it is wet with oil, this is an entry route. A quick fix for this is a separator from Steeda, Home Depot, or Lowes. For about $25 (The Steeda unit will be more expensive) for the separator and fittings you will be able to remove most of the oil before it gets to the intake.
Also, you need to verify that the PCV screen is in place. This often forgotten part is located underneath the PCV in the back of the intake, and helps remove oil mist from the crankcase gasses.

Contributed by tmoss...
I have seen a BUNCH of intakes (100s) and you can tell the lower intakes that were on cars whose PCV screen had been blocked - they have a very thick coat of grime on the bottom of the lower intake. You know the heads had a nice thick coat below the rockers too as the blow-by had no where to go. When you put the intake in a solvent tank and wash it, it does not cut all the crud off - reason? - the blowby gasses will not come off with safety solvent. why, I don't know.
Do your self a BIG favor and install a PCV screen once a year.

If a compression test comes back normal, and the above mentioned lines are dry, then the valve guides are suspect.

The PCV Problem
Many of the Fox Body Mustangs seem to have serious issues with oil consumption through the PCV or Throttle Body/Valve Cover line. There are 3 main causes of this problem.
1. Excessive Blowby
2. Removing the Valve Cover Baffle at the oil filler neck
3. Removing the Baffle and/or the PCV Screen on the lower intake
However, in some head/cam/intake (and possibly stroker) combinations the problem can persist.
Sometimes a small oil/air separator can be used to help filter out the oil before it gets to the intake manifold. Most who run this setup will remove the small plastic filter, as it tends to plug up and restrict airflow. An oil/air separator is a band-aid solution though, and should not be considered permanent. The goal should be to completely eliminate the flow of oil from the crankcase.

The problem seems to be that the stock PCV line does not flow enough volume to allow adequate ventilation in modified motors. The lack of volume flow creates a build up of pressure in the crankcase which forces crankcase gasses through the PCV at higher velocities. With the added velocity the crankcase gasses are able to pick up more oil vapor; carrying it into the intake manifold.
Yet another issue is that the stock single PCV system can create rather long flow paths for pressure to vent. For example gasses in the front of the crankcase would have to flow to the back of the block to exit through the stock PCV. The result of a long flow path is that it will take longer to purge the crankcase pressure.

The solution is to allow a greater volume of gasses to vent from the crankcase, at lower velocities. This can be done with a larger ID PCV hose and PCV, or by adding a second PCV line. Since larger ID PCV valves can be hard to find the easiest solution should be to add a second PCV line to the drivers side valve cover.
The stock drivers’ side valve cover can be replaced with any valve cover that has an oil filler/breather hole. What valve cover is used does not matter, so long as there is a way to mount a PCV valve to the valve cover. A stock passenger side valve cover installed on the drivers’ side would work well, or many of the aftermarket valve covers have holes intended for mounting breather caps.
The hose from your new PCV should flow either directly to the intake manifold (parallel to the stock hose), or merge with the stock hose. An air compressor oil/air separator can still be used to filter out any oil that does get out of the crankcase. However, if the system is setup right and the motor is healthy, there should be very little oil accumulation in the separator if any at all.

Secondary Benefits
The increase in the volume of air that can flow out of the crankcase means lower accumulations of harmful Blowby gasses and moisture. Also, lower crankcase pressures will allow greater efficiency and power (although this affect is probably minimal on a street car).

More Notes on Installation
1. It may be better to install the drivers side valve cover PCV toward the front of the motor. This will allow a shorter path for gasses that are trapped in the front of the crankcase.
2. It may not be a good idea to install a third PCV on the aft side of the passenger side valve cover, as this could allow fresh air from the TB/VC hose to vent directly out that PCV. This would result in no fresh air hitting the crankcase, and a greater accumulation of harmful crankcase gasses and moisture.

Extra Notes
From what I have seen, the oil accumulation in the intake will be greatest when the car is left to idle for some time (stuck in traffic or idling in the driveway), and then with some rpm the oil is picked up and thrown into the combustion chamber. If you live in a humid part of the country, or see a fair amount of condensation on the ground in the morning, then you will most likely notice some moisture in the separator, resulting in the easily recognized brown milkshake appearance of the oil in the separator. This is fairly normal, as overnight condensation will form on the inside of the engine block. Once the oil gets up to temperature, this moisture boils off, and collects in the separator.
Title: Re: PCV and breathers
Post by: onederful100 on March 28, 2010, 08:31:21 AM
this is the breather that i have on the oil filler cap

heres one for 86-04

my breathers on the valve covers are K&N, can get at Rons or order from jegs or summit if Rons no more in stock.

for the s197 the K&N part #'s for the valve cover breathers are:
62-1320 (3/8) passenger side
62-1340 (5/8) driver side
Title: Re: PCV and breathers
Post by: onederful100 on July 13, 2010, 07:31:49 AM
some great info on this thread. 
check valve also used to cut down on blowby.
but different ways to cut down or eliminate blowby.
Title: Re: PCV and breathers
Post by: onederful100 on March 14, 2015, 05:35:04 AM