I'm running two PCV valves to the plenum on my 406 and no breathers. The crankcase is at manifold vacuum. I have oil separaters on both lines and so far they haven't picked up any oil.

I was running 1 PCV and a breather, but that was basically a vacuum leak and it was sucking a lot of oil......would fill the separator (a compressor filter) in about 300 miles. I've only driven about 20 miles with the double PCVs, but not a drop of oil yet.

Any problems with this???????

 

I'm guessing but 2 PCVs in parrallel shouldn't change much but airflow through the crankcse and bypassing the carb will increase - yes a bigger controled vacuum leak. But thats what just 1 PCV does so i'm guessing u can adjust carb mixture (if u have a carb) - yes carb jetting.
But did u try using just 1 oil separator (and only 1 PCV)? Its hard to see from out here in California if ur valve cover has a baffle under the PCV? This would be my first fix. That baffle blocks rocker oil splash at the PCV and not all vc have them under all the holes.
Not to slam ur good effort here but i kind'a like those circle track vc with the tall filtered vents. 2 big filters on 1 side and the correct PCV over a baffeled vc would be my choise for crankcase pressure problems.
Good luck. cardo0

 

I think i read that they can fight each other,, not sure???

 

Cardo....both tall valve covers and baffled. I've tried a few configs already. With 1 PCV and no breather, i was building up crackcase pressure at WOT. WIth 1 PCV and breathers, it becomes a vacuum leak and moves a lot of air and oil with it. I had to add a separator to prevent oil from being pulled into the intake. I've been driving this way until now...but the vacuum leak is sort freaking out my computer a little (slight miss cruising at 1500-2000rpms). With no PCV and just breathers, i'll get oil fumes if i sit in one place too long.... like a long traffic light. With both PCVs hooked up, the crankcase is under vacuum and doesn't move much air. So far i have picked up any oil in the separators. My concern is building pressure at WOT...but i'm hoping with 2 PCVs, there'll be enough ventilation. My other concern is contaminating the intake air. I guess i'll find out at my next trip to the track.

Any other concerns???? It's too siumple a fix to actually work

 

Ralph,
I am trying to figure out what went wrong with the single PCV and the breather. That is the stock set up, and should work fine. I think the oil filling the separator could be addressed, but the "vacuum leak" is troubling. Was the PCV valve possibly defective? Installed backward? I don't understand how the "stock" set up causes a vacuum leak, bigger than stock. Two PCVs would be worse, if there were fresh air available to the crankcase, and I don't understand the point of two, without it. I share your concern about a pressure build up at WOT, and also, I have concerns about a vacuum at times other than WOT. Race cars use vacuum evacuation pumps for the track, so a vacuum at WOT, wouldn't be a concern for the brief runs down the track, but vacuum all the rest of the time is going to put a strain on seals and gaskets, besides having no crankcase ventilation. Besides not being healthy, I'm afraid a build up of blow by gasses and an errant spark could cause a crankcase explosion. *I* would working on some variation of the stock set up. A breather for air in, and a PCV to circulate it. THEN, if you desire better circulation at WOT, consider a header based evacuation system, in addition. With the stock system, and no vacuum in the manifold at WOT, there is no "forced" circulation on the track, but no pressure build up either, because of the breather. The header system draws little or nothing, except at WOT. A dual system would give you both. However, I doubt you really have to provide actual circulation for the brief periods of WOT. Good luck, and...

RACE ON!!!

 

Jim, if you remember, when i had just the stock setup, i blew out the seals on the intake rails, splattering oil onto the water pump. Then i installed breathers in both valve covers. That relieved the pressure, but then i started sucking oil into the intake. Adding the separator solved that problem, but the PCV basically became a vacuum leak which is contributing to this bucking problem i'm having with the converter locked at low rpms. With 2 PCVs and the crankcase under vacuum (no vacuum leak at the intake), there's much less air movement thru the PCV system (so i'm not sucking oil) and it will only vacuum out blowby. At WOT there are two escape paths (thru both PCVs) for any crankcase pressure due to blowby.

Jesse is running a sealed crankcase as well with a combination of PCV in one valve cover and evac system in the other putting his crankcase under vacuum. I believe Corky is running the same double PCV system as i am now, but not sure. I'm afraid it's all too simple tho...so it can't really work

Not sure i follow your logic on the crankcase explosion....but you do have my attention. My thinking is when there is any manifold vacuum, it will suck up any blowby and at WOT any presure can escape thru the PCV system....assuming it's adequate. Maybe i'll put a vacuum guage on the dipstick and see if it builds any pressure at WOT. i WILL also bring my breathers with me to the track next time just in case.

 

THAT should have tipped you off to excessive crankcase pressures, from the start. Of course there is less air flow. There is no source of fresh air. The intake vacuum is aggravating an already bad blow by problem. The only intake to your crankcase is past the rings. During full throttle, a vacuum in the pan can aid ring sealing, but as you're set up, WOT is the only time you DON'T have vacuum in the crankcase. My thinking is that without fresh air entering the crankcase, escaping blow by gasses can only be replaced by more blow by gasses. And that without circulating fresh air, the gasoline laden blow by gasses will build up to dangerous levels. Take an extra moment or two, to digest some of my last post. There is more in there than it first appears. I DO hope you get this worked out.

RACE ON!!!

 

Thanks for input Jim....

addressing your earlier post....the vacuum leak was due to having breathers in both valve covers.....therefore the PCV was just sucking air like an open vacuum line.

i now understand your point about volital gas build up in the crankcase, however is this not the same situation with a vacuum pump. I assume that system doesn't introduce fresh air to the crankcase to maintain vacuum. I also had a 280Z that used to have it's crankcase under vacuum. I know there's probably something wrong with the setup i have now or they would have done it from the factory...although it seems to be working fine cruising around so far. I think i'm going to throw a vacuum gauge on the dipstick and see if it builds any pressure under heavy load. If this does't work, i give up and will just run some hoses off the valve covers to under tha car somewhere and plug the vacuum lines.

As for the blowby, not sure why it would be so bad. I've got 195psi cranking (exactly what is should be) and 5% or less on leakdown....all cyls within a percent or two on both measurements. And it's not running terrible track times. But there's no question that there a lot of air/gasses running thru the crankcase. Maybe those intake seals blew out before the rings really had a chance to seal...i dunno.

 

You can try restricting the vacuum line to the PCV if you use open breathers. Basicly meter the vacuum leak. The dimension I remember reading is like 1/16" hole.

I can tell you that with a single open breather in one valve cover and a PCV valve in the other cover, that wasn't hooked to a vacuum source, that a 383 that I'm working on, built up enough WOT pressure to push enough oil out the open breather to start a small fire on the header, and leave one hell of a smoke screen. Adding a second breather instead of the PCV lead to very little blowby out of the breathers. A little weird, but true. I like the Chrysler type, just make sure you seal the crimp area or they will leak. You could tie 2 of those into a small vented puke tank. Then have a PCV valve with a restrictor in the line. I just don't like the idea of oil vapors contaminating the intake mix at WOT.

 

I have a pretty good idea of what is needed, but I must be a little weak on how, EXACTLY, everything works. I see a problem with a breather in both valve covers, used with a PCV valve. The air will follow the path of the least resistance, and travel from VC breather opening to the PCV opening, in the same VC, without picking up any of the crankcase gasses from below. However, I don't expect the path of least resistance to be so MUCH different than from the opposite side as to cause your "vacuum leak". I am thinking the "vacuum leak" is caused more by the PVC VALVE than by the way it was connected. Don't those things, self meter, to prevent too much flow and the "vacuum leak" you experienced? I always thought so, but THAT is an area my knowledge is a little weak.

*I* think the proper set up is basically the stock system. The Chrysler breathers, mentioned above, are supposed to have excellent oil separators in them. I would aee about using two of these. One connected to a filter, for the crankcase vent intake and the other connected to the PCV valve.. Then make sure you have a properly operating PCV valve.

Leaky intake seals would only help to SOLVE your breathing problem. They would apply additional vacuum to the crankcase and help acerbate the the pressure build up.

RACE ON!!!

 

I don't know if the PCV valve is self metering. When i say a vacuum leak, i mean thru the PCV valve. If i suck on the PCV valve, there's very little restriction....and i've tried 3 different valves. do they make different tension PCV valves? Maybe a 350 valve is not restrictive enough for a 406?

Last night i tried blowing thru the PCV valves, separators and hoses connected to the intake and it was pretty restrictive, so i expect too pressure to build up at WOT. I'm probably going to eliminate the PCV system and just vent the valve covers out under the car. No vaccum leak, no pressure build up, no sucking oil into the intake and hopefully no fumes under the hood or in the car........don't know what else to do at this point.

 

There are different tensions in the PCV valves. I've never seen a good definition of how the numbering system works though.

My idea with the 2 breathers, and the PCV is to create just enough flow to keep the oil vapors out of the engine compartment. The Chrysler breathers are really just canisters with some screen and a piece of foam. They do work well though. I'd think the oil soaked foam would create enough restriction to get a little flow from the opposite side of the motor. If you really wanted to get **** about it you could have a pcv valve in each valve cover, T'd together to a single vacuum source. The restriction of the PCV line is the big thing. Pull the PCV valve out while the motor is running and put your thumb over it. You've got a huge vacuum leak there, pulling a lot of air. Then with it out, cover up your 2 holes in the valve covers and see how much pressure is actually built up. It shouldn't be much. All you want to do is put in a little pcv air flow to keep the oil vapors down.

I'd expect to see oil pushed out of the open breather at WOT with the way CFI mentioned above. A single breather will create a higher velocity of air out the breather tube, and carry more oil out. The second breather cuts that down.

The stock system also takes into acccount the pcv air that's allowed into the motor, so it's fueled properly. That's where your high vacuum, part throttle miss is coming from.

 

The miss is more pronounced with the PCV hooked up with both breathers. With the PCV blocked, it's still there, but much less noticable. That's one of the reason i'm trying what i did...to get rid or the miss or surge at equalibrium cruising or deceleration. With both PCVs hooked up and no breathers, there's no vacuum leak and no fumes and no pressure on the crankcase while cruising. But I'm guess'n at WOT, too much pressure is going to build up.

A stiffer PCV valve might help tho. with breathers to vent WOT pressure and PCV to keep the fumes down while idling or cruising....but not just a huge vacuum leak. i dunno

 

And no crankcase ventilation.


*I* think with a breather in each VC, the air flow will be from the breather on the PCV side, straight to the PCV valve hose. With dual breathers, you won't get any pressure build up, but I'm afraid you won't get any air circulating through, to ventilate and purge the blow by gasses.

RACE ON!!!

 

Jim.....what do you recommend?

The current dual PCV system will probably have too much back pressure at WOT....I'm not THAT concerned about circulation cause any nominal blowby will be sucked into the PCVs....so there will be some circulation.

Mulitple breathers short circuit the PCV system and basically create a vacuum leak that is contributing to unstable cruising & deceleration (bucking).

Breathers with no PCV valve solve the vacuum leak, but oil fumes become an issue, in additonal to your concern about circulation. Although i know of several examples running this way.

Stock setup didn't provide enough ventilation in the past. Things might be better now that the rings have seated better. However the PCV would still be contributing to the bucking problem. This also necessitates the use of separators to stop the intake from ingesting oil. This might be worth another try tho, maybe limiting the volume thru PCV system somehow.

Other than that, i'm outa ideas.

 

I will try to address your post, point by point. Certainly I am no expert, and there are a few problems, here, that have me concerned. My problem with this, the ONLY inlet for the PCV valve is the blow by. Therefore, there is no replacement for blow by gasses, other than more blow by gasses. I feel that fresh air needs to be introduced to keep the crankcase purged of excess blow by. In addition, the vacuum in the crankcase at part throttle (most of the time) only encourages more blow by. I agree with the "short circuit" part. The air flow doesn't pass through the pan and evacuate the blow by gasses. What I don't understand, is the vacuum leak. You say you have tried different PCV valves, but I still think it shouldn't pass enough air to act as a vacuum leak. I would guess that I have as much vacuum at idle as you do, because of your cam. I can pull my PCV valve out of the VC and let it suck fresh air, with no ill effects on the idle or drive-ability. *I* think there is some sort of problem, there. Agreed. And no fresh air circulation, down below. Not ENOUGH ventilation seems to be the opposite of the vacuum leak problem. Maybe the rings HAVE taken a better seat. Possibly the crankcase pressure build up is no longer a problem. Or maybe excess crankcase pressure is "supercharging" the PCV and pushing extra air into the intake, causing the vacuum leak symptoms. I think with a healthy oiling system and also without stock valve cover baffling, oil separators are going to be necessary.

I see three problems that have to be addressed.
1.) The way *I* see it, you are going to have to use oil separators.
2.) Check for and correct excessive blow by.
3.) Figure out WHY the PCV valve provides so much air, that is acts as a vacuum leak.

Then, you SHOULD be able to use the stock configuration of a air inlet in one valve cover and a PCV in the other. I hope this helps.

RACE ON!!!