PCV systems

PCV stands for "Postive Crankcase Ventilation." Alot of people misunderstand the benefits of a properly functioning PCV setup on their cars. Some see oil in the intake and IMMEDIATELY blame the PCV system and begin to eliminate it all together. This is NOT always the best solution.What purpose does it serve on MY motor?

The word "Postitve" in "Positive Crankcase ventilation should be replaced with "Active" in my opinion. It makes more sense in MY mind. The reason I say that is b/c in a properly set up PCV, the crankcase itself isn't just pushing out pressure but its actually being "scavenged" or "drawn upon" but the intake, via the PCV Valve. This beats the "old school" breather setups, especially during part throttle (intake under vaccum) situations. Picture two jars side by side. Both filled with smoke (relates to crankcase fumes and pressure). Open BOTH jars. Take a vaccum to one jar and leave the other one open to the atmosphere....which one clears out most effectively and quickly? This is how a PCV system benefits....BUT they have to be setup properly!

Two things in the crankcase that a PCV helps eliminate are 1) The most common problem PRESSURE! and 2) Detergents and Toxic fumes. Pressure in the crankcase is bad for MANY reasons. It slows down pistons on their downward travel during the intake and power strokes, negatively affects the sealing of piston rings to the cylinder walls, and can blow out seals and gaskets on the motor itself. Fumes in the crankcase are bad for the enviroment but also can act as solvents and begin to break down oil in the crankcase, leaving your internals less protected!

SO how does it work exactly? Its kind of hard to draw out so I'll explain it from the PCV valve forward. Your PCV is mounted in the backside of the lower intake. The hole it is mounted in, leads to the lifter valley (Keep this in mind...the Lifter valley shares the SAME volume of air/gases as the crankcase and area under the valvcovers! Crankcase pressure is in ALL these areas! IT IS ALL THE SAME AREA! I'll explain why this is red later.) It is this area that must be vented! The PCV is connected to the upper intake plenum via a large vaccum line. It is HERE where the ventilation takes place! The engine, when running, is sucking on this hose...hence vaccum line...which draws on the crankcase! VOILA! POSITIVE VENTILATION! BUT WAIT! In order to ventilate...you have to MOVE air...not just creat a vaccum! PAY ATTENTION! This is where ALOT of Mustang owners screw up! Remember that little black hose from your oil filler neck to your intake tract that you probably tossed in the trash and replaced with a breather? Do you REALLY know why that leads into the intake tract? Many of you would say "Because of the that pesky EPA and their stupid emissions!" WRONG!!!!

Think of the crankcase as your musty *** bedroom after you haven't done laundry for a month! Opening the door and putting a fan there is good...but you can move MORE air ACROSS the room if you open the window and have the fan DRAW IN FRESH AIR from outside across your stankin' room and out the door! A PCV works on the SAME principal! Makes sense now huh?

Now you're probably saying "Well, the breather does that just fine!" Yeah it does...BUT you also just created a vaccum leak! Meaning your engine is now ingesting UNMETERED (Air that has NOT been measure by the MAF). THIS CAN CAUSE THE DREADED IDLE SURGE QUICKER THAN YOU CAN SAY "PVC." Now I've seen some cars, my own included where this wasn't an issue, BUT I've also seen it wreak havoc! How are you drawing unmetered air you ask? Well...but pulling off that little black hose and tossing it for a breather on your oil neck because you think it looks "trick" next to your cold air, you opened that neck up to the atmosphere...where before if was drawing on metered air from the intake after the MAF. This newly unmetered air travels down the neck, into the valve cover area, down to the lifter valley, up the PCV valve, and on in to the intake to wreak havoc on your idle. (Remember the red text above? That is why I wanted you to understand how the crankcase is one big open area).

THAT is how the stock PCV works and WHY it is setup the way it is....

Under normal circumstances, the vacuum created by the engine would suck air through the PCV valve and into the upper intake. That would clean the "bad" air and blowby out of the crankcase and it would get replaced with fresher air that will, in turn, remove more contaniments from the crankcase. Of course, the PCV valve is one-way.

So what happens when you add a supercharger? Well when you hit WOT and the RPMs start rising, the engine goes from naturally aspirated to boosted. This means that there is no longer a vacuum; instead air is getting forced into the engine. Now remember that line that ran from the upper intake to the PCV valve? Since the intake manifold is now under presure, airflow is reversed in that line as well.

Of course, if you have a good working PCV, then it will close and prevent that boosted air from entering the crankcase. However, don't forget that there is still going to be some blowby...and now that you've increased pressure, there's going to be even more blowby than when yo were N/A. And then remember that tube that ocnnects the valve covers to the throttle body? Well that's not one way. Air will reverse direction in that tube as well but this time it will actually reach and pressurize the crankcase. So now you have blowby getting into the crankcase along with air being forced in through the valve covers.

Before, that blowby and excess presure could be vented through the PCV. But now since it is temporarily closed, the pressure has nowhere to go. Now it's going to start looking for a way out (seals, gaskets, or more often, the oil dipstick.)

If you add breathers to the valve covers, this will give the crankcase a way to relieve the pressure. But then when it's running N/A you create a vacuum leak... The upper intake will suck air from the crankcase via the PCV valve. As the air gets sucked from the crankcase, it needs to be replaced. It will take that air from the breather caps, suck it into the crankcase, through the PCV, and into the upper intake... Thus introducing unmetered air into the engine...and that is bad.

A solution... remove the PCV system and convert it to a Breather type setup. To do this, remove the tube that connects the oil filler tube to the TB and cap it off on the TB side. Take the oil filler tube side and vent it to the atmosphere (or replace the entire valve cover and just pop on a breather instead.) Take the tube that connects the PCV to the upper intake and disconnect it from the upper intake. Plug the nipple on the upper intake side and let the tube (which is still connected to the PCV valve) vent into the atmosphere as well. Now add a breather to the opposite valve cover. A lot of times, people will place this tube right next to the filter on the inlet side of the supercharger. That helps reduce the smell of fumes in the engine bay and passenger compartment.

Now you will have a way to releave crankcase pressure without creating a vacuum leak.