PCV System Theory of Opertation and the Alternatives. (Updated 4-02-07)

ryclef331

Well-Known Member
Joined
Jan 20, 2006
Messages
2,913
Reaction score
11
I'm going to start this article tonight. I'm typing as this all comes to me. THEN i'm going to go back, edit it, and add pics. SO bare with me.


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. Below is a VERY basic diagram on how the FACTORY PCV system works on a 94-95 5.0. It consists of a PCV Valve (located in the backside of the lower intake), and various vaccum lines.

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 ass 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....

Ok so we know how it works. What is wrong with it? Well for starters...the #1 complaint you'll hear is "There is oil in my intake!!! HOW DID IT GET THERE?!" People hear "PCV" and flip and yank it all off. How does the oil get in the intake? Well, all those moving parts in the engine can REALLY get moving and splashing oil around. Those splashes make "oil mist." Its the mist that gets sucked up through the PCV and puts a nice coating on your intake. Now if you have a poweradder, or a higer milage motor, you generate more blowby and there for push MORE oil into the intake. ALSO, what can happen is HIGH RPMs with HIGH vaccum (i.e. you just made a 1/4mile pass and are at 5,000RPMS in 4th gear and snap the throttle shut and let the motor slow you down or "compression brake"). This generates EXTREMELY large amounts of vaccum in the intake as the motor is still spinning VERY fast but trying to suck against a closed throttle body so something has to give....alot of oil mist from the crankcase is what comes in. I personally, never down shift unless I'm corner carving. At the end of my runs, I throw it in neutral and let those things on each wheel that are designed to slow you down do their jobs. Thats me.

Now, I had an 02 Lightning for a little under a year and ask ANY 2nd Gen. Lightning owner about oil in their intake and they can tell you a story for sure. They were EXTREMELY prone to it as the engine AND blower would suck LARGE amounts of oil from the passenger side cam. Well, owning that lightning taught me two things....1) How to get rid of it and 2) what it does to your motor. After doing LOTS of reading, I learned that oil mist can actually LOWER the octane of your fuel...but I don't see this as being TOO much a problem b/c I never ONCE read about a lightning owner blowing his or her motor due to oil in the intake causing detonation. As delicate as lightning motors were, I think Ford would have definetly recalled a truck or two if such were the case.

How do you get rid of it? SEPERATE IT! After I bought my Lightning I realized that I too had ALOT of oil in my intake. I read about 50 million different ways to eliminate it. Alot of them were buying kits from reputable manufacturers (steeda, lightning force performance, etc). MANY shunned what I'm about to tell you but I tell you right now....Look at the picture of a $60 steeda oil seperator kit...and look at my $30 Home Depot setup.

You be the judge....

$70
STEEDA
555-3710-lg.jpg


$10 @ lowes + whatever you spend on the 3/8" Barbed fittings and vaccuum line..

045564616823.jpg


I put the cheap-o setup on my oil swilling lightning and what do you know! My intake was dry as a bone the rest of the time I owned the truck! You can also see it work. Check it whenever you fill up on gas and just drain the bowl back into the oil. This setup of would go in the line between the PCV Valve and the port on the lower intake. Just cut or extend or replace the factory hose with two pieces of hose and this in the middle.

If you car is consuming an unnaturally large amount of oil though, you might have bigger problems Excessive blowby (i.e. your rings are taking a dump on you) can increase cylinder pressures and cause the excess oil in the intake. A seperator is not a band aid for this....

THE OTHER bad thing about the factory PCV is that it is TOO SMALL! Its only 3/8" in diameter. I've got a 331 stroker that I turn to 6500 and spray with 150-175 shot of nitrous. My compression is GREAT BUT I build so much crankcase pressure that it overwhelms the stock setup and I would come back from a run and find my dip stick sticking half way out of the tube! This can also be the cased for Turbo/Supercharged cars where they actually pressurize the intake which inturn, tries to close the PCV valve (which is a one way valve, remember?) so it will slow down the process of scavenging the crankcase ALOT. Solution? Ditch the PCV setup.

On my personal car....neither my intake (Victor 5.0) nor my valvecovers (JEGS custom cut) have provisions for PCV so it was a no brainer. HOWEVER, on your stock or close to stock car, you have to plug the PCV Valve in the back of the intake! I would just cap off the valve itself with a vaccum cap. Now, you can just cut a couple of holes in each valve cover and use some "push in" style breathers from pretty much ANY parts store! I would make sure to run atleast two (one on each) to allow adequate ventillation. The biggest CON to doing this is the same as a stock PCV Setup....OIL MIST! While it isn't in your intake this time, it can make its way down onto the valvecover...and if bad enough the headers making for a fire hazard. For this reason they sell baffled breathers and catch cans. Catch cans operate in much the same way the steeda seperator kit above does...just on a larger scale. You can find them at summit, jegs, and ESPECIALLY on eBay. After looking at the construction of one...I elected to make my own.

I use two 3/4" fittings tapped into the back of each valvecover and then they merge into a 1" piece of braided pvc tubing...into my "homemade" vented catch can.

225761073.jpg


The can is filled with steel wool. The wool acts as a filter...catching all the mist on the strands. Eventually the oil puddles at the bottom of the can. Thats where the size 6an drain comes in handy.

There you have it. Thats the ins and outs of a pcv setup. Any add ons, questions or comments...FEEL FREE!!!
 
Joined
Jan 21, 2007
Messages
190
Reaction score
0
Re: PCV System Theory of Opertation and the Alternatives.

Good write up, I am putting a breather instead, and plugging the holes in the intake.
 

Downshift

Well-Known Member
Joined
Jan 21, 2006
Messages
1,957
Reaction score
0
I will probably be going the home depot way lol because im cheap but like to do things myself. Whats that thing called in the second pic? The one that says kobalt on it? I know I have seen them somewhere... just cant think of a name. Thanks.
 

ryclef331

Well-Known Member
Joined
Jan 20, 2006
Messages
2,913
Reaction score
11
5.0wned said:
I will probably be going the home depot way lol because im cheap but like to do things myself. Whats that thing called in the second pic? The one that says kobalt on it? I know I have seen them somewhere... just cant think of a name. Thanks.

Ask for an air compressor filter or air water seperator.
 

Trickflow.GT

Active Member
Joined
Nov 23, 2006
Messages
463
Reaction score
0
i dont know what to think now...is it good to keep the pcv system or bad?
 

ryclef331

Well-Known Member
Joined
Jan 20, 2006
Messages
2,913
Reaction score
11
I put up both sides of the story so you can make your own choice! Sucks huh?
 

samseed101

New Member
Joined
Jan 27, 2007
Messages
19
Reaction score
0
I know I'm the new guy here, but I'd like to add a small writeup about the PCV system when dealing with supercharged applications. On another site that I frequent, I often see peopel ask why their oil dipstick is blowing out or why they're blowing seals with their newly installed supercharger. Many times, it's because they misunderstood how the supercharger and how the PCV system works. So I wrote this little piece and I usually cut and paste it to respond to their questions.

If this applies to this forum and section, feel free to keep it. I know a lot of it repeats what was stated above in the original post so if you want to edit it or cut it out feel free. I just figured I'd repost it in its entirety incase someone with a supercharger comes along and is having problems.

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.

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.
 

ranger50toy

New Member
Joined
May 3, 2007
Messages
82
Reaction score
0
What about both. Is there a breather that will allow excess pressure to escape, but not allow a vacuum leak? One that has another 1-way valve inside.
 

samseed101

New Member
Joined
Jan 27, 2007
Messages
19
Reaction score
0
ranger50toy said:
What about both. Is there a breather that will allow excess pressure to escape, but not allow a vacuum leak? One that has another 1-way valve inside.

While I have technically never seen one, I think I could probably fabricate one. I'd probably take some vacuum line and fit the end of it with a check valve from a brake booster. In theory, that would allow the air to flow out under pressure, but it would prevent air from flowing in in a vacuum situation. However, once you do something like that you might as well completely disable the PCV from the upper and lower manifold as well. And there's a very good chance you can cause other problems by doing this as well.

The PCV system get's it's "fresh" metered air from the TB and pulls it into the crankcase via the passenger side valve cover. If you plug off the TB and make the tube on the valve cover a one-way valve, you prevent fresh air from getting into the crankcase. But there's still a vacuum because you would still have the PCV connected to teh upper intake.

In other words, you can do it but it's pointless because you'd be better off completely disabling the system to begin with (which I ONLY recommend doing on a forced induction engine)
 

ryclef331

Well-Known Member
Joined
Jan 20, 2006
Messages
2,913
Reaction score
11
samseed101 said:
ranger50toy said:
What about both. Is there a breather that will allow excess pressure to escape, but not allow a vacuum leak? One that has another 1-way valve inside.

While I have technically never seen one, I think I could probably fabricate one. I'd probably take some vacuum line and fit the end of it with a check valve from a brake booster. In theory, that would allow the air to flow out under pressure, but it would prevent air from flowing in in a vacuum situation. However, once you do something like that you might as well completely disable the PCV from the upper and lower manifold as well. And there's a very good chance you can cause other problems by doing this as well.

The PCV system get's it's "fresh" metered air from the TB and pulls it into the crankcase via the passenger side valve cover. If you plug off the TB and make the tube on the valve cover a one-way valve, you prevent fresh air from getting into the crankcase. But there's still a vacuum because you would still have the PCV connected to teh upper intake.

In other words, you can do it but it's pointless because you'd be better off completely disabling the system to begin with (which I ONLY recommend doing on a forced induction engine)

Agree 100%
 

scootin95gts

Active Member
Joined
Feb 14, 2007
Messages
277
Reaction score
0
okay the past owner on my car put new valve cover on my car and all i got is the pcv valve from my lower intake running into my upper intake is this okay? also on my cai the prev owner put on there isnt a tube going into that just the sensor and the maf is this okay also? cant think of that tube maybe rycleff can lol
 

ryclef331

Well-Known Member
Joined
Jan 20, 2006
Messages
2,913
Reaction score
11
"The PCV system get's it's "fresh" metered air from the TB and pulls it into the crankcase via the passenger side valve cover. If you plug off the TB and make the tube on the valve cover a one-way valve, you prevent fresh air from getting into the crankcase. But there's still a vacuum because you would still have the PCV connected to teh upper intake."


As mentioned above, it will STILL pull vaccum on the crankcase but you're not getting optimal ventillation on it. You want to figure out someway to hook a valvecover into the intake tube, BEFORE the throttle body and AFTER the MAF. This will complete your PVC system. Anyway you want to do this. Get creative. The parts store will have everything you need. Vacuum line, barb'd fittings, etc....
 

scootin95gts

Active Member
Joined
Feb 14, 2007
Messages
277
Reaction score
0
well i cant really see if but one line i got going directly to my pcv and th one beside it is capped and i also do have my egr del and smog,but if i get a breather cap like that one where would i run the line for that cap at?
 

ryclef331

Well-Known Member
Joined
Jan 20, 2006
Messages
2,913
Reaction score
11
from THAT cap, run the line to your cold air intake...after the MAF and BEFORE the Throttle Body.
 

Lane478

New Member
Joined
Jul 10, 2007
Messages
65
Reaction score
0
One thing I have not found is a diagram of how the factory PVC systems is routed. Delk did a PVC mod on my car to reduce emissions and after learning better, I want to put it back factory. Does anyone have a layout of the vacuum routing for it and any other vacuum lines that are connected to it?
 

ryclef331

Well-Known Member
Joined
Jan 20, 2006
Messages
2,913
Reaction score
11
its simple.

On your oil filler neck, there is a nipple. From that nipple a vaccum hose runs to you intake duct....there should be a nipple there as well. Run a line between them. The one on the intake tract needs to be AFTER the the MAF and BEFORE the Throttle Body.

On the back of the lower intake is where the PCV Valve is located. Run a line from there to one of the large ports on the bottom side of the upper intake.


Thats it. THAT is your factory PCV setup routing.
 

Lane478

New Member
Joined
Jul 10, 2007
Messages
65
Reaction score
0
Uh-oh :-[ I got a vacuum tree on my hose running from the rear intake that has a smaller hose that runs to the small vacuum block connected to the EGR system, but that's O.K. I just got the Ford Factory service manual for a 1995 mustang. This thing has everything. I'll get it fixed now! Score! :boink:
 

ryclef331

Well-Known Member
Joined
Jan 20, 2006
Messages
2,913
Reaction score
11
that vacuum tree is good. you need it as well. The PVC line goes to the BOTTOM of the upper intake. You gotta reach under it.
 

Downshift

Well-Known Member
Joined
Jan 21, 2006
Messages
1,957
Reaction score
0
I did the Kobalt filter like you have in the second pic, but something I forgot to ask. The little nipple thing on the bottom, did you plug yours or just leave it alone? It makes a small whistle noise and even if I turn the little switch on the side of it, it still sucks air in. Not sure what I should do there...
 

ryclef331

Well-Known Member
Joined
Jan 20, 2006
Messages
2,913
Reaction score
11
The nipple on the bottom is a drain for any oil the seperator traps. It should be making ANY noise. It should be sealed.
 

Forum statistics

Threads
74,996
Messages
1,454,276
Members
13,629
Latest member
KillaMustang04

Members online

No members online now.
Top