Stay With PCV!

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mflynn

mflynn

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Just thought I'd post about my recent experience. Rebuilt the top end of 318 in my '68 Barracuda. New cam, valve springs, rockers, lifters, rods, timing chain, Holley 4 bbl, Edelbrock Performer manifold. Also wanted to dress it up a bit, so I slapped on some chrome valve covers with breathers only. I read a lot of posts about pros/cons of ditching PCV, from which I gathered that it could be done. When I first put it back together, I was blowing oil through the manifold-to-block mating surface on the rail closest to the firewall. My bad - first timer on this, I didn't use enough RTV (despite many awesome posts on this subject advising not to skimp!). So I pulled the manifold off and got it right the second time. Then after a few rides, the manifold was sealed tight, but I was getting oil shooting through the breather on the passenger side - i.e. same side as where PCV had been originally. So I went back to the original covers with a new PCV and that seems to have solved the problem. I've put about 100-125 miles on it since and she hasn't leaked a drop of oil. I am no mechanic and - at least at the beginning of this resto almost 3 years ago - I was a complete novice. I hope this might add some helpful food for thought to anyone else trying to decide whether to stay with PCV or not, but I'd also welcome comments from the experts out there who might help offer alternative explanations/suggestions. Thanks!
 
It's hard to say........what exactly did you have for ventilation to start with? Or, you may have some engine problem causing abnormal blowby. All engines I've been around had a "flow" through the engine, getting clear back to the old "road draft tube." So a big open breather somewhere up topside, and a road draft tube towards the "other end" of the engine extending down below. Both were baffled and had rudimentary filtering......oil soaked steel wool.

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My truck has the breather off the valve cover hosed directly to the side of the air cleaner housing outside the element footprint, It is sealed 'cept for the snorkle on the other side. It has a loose fiber barrier in the air cleaner capping the crankcase inlet. My 57 Ford had the road draft tube, nasty thing. the slant had it coming off the rear valve cover breather. It also has a PCV valve going to the base of the intake so the valve cover tube is more of an inklet than an outlet, but I get plenty of blowby when the filler cap on the common valve cover is off. all that ends up going out that air cleaner hose at idle. You need PCV (or some sort of directed crankcase ventilation) or it will just blow out everywhere it can creating a dangerous flammable mess.
 
After your upgrades there may be increased crankcase pressure on the lower end of motor (i.e. ring seal). No amount of ventilation will solve bad sealing rings. Only a leakdown test can determine this. Please bear in mind that a PCV only works at high vacuum situations such as idle or low rpm cruise. Also, the PCV should be connected to a nipple on the intake manifold. In addition, a tube connecting another breather to the air filter housing will draw vapor when the PVC isn't functioning. An oil pan evacuation system may also be helpful, (about $39.00 from Summit or Jegs) which is attached to the exhaust and creates a vacuum in the crankcase and at the same time can increase h.p. by 10-15. Hope this helps. Later.
 
My 434" small block made 3 more hp on the dyno with the pcv hooked up.
 
Had problems with my 416 put breather on passenger side hooked to the air cleaner.Purchased an adjustable pcv valve from wagner .It allows you to adjust your idle flow based on the cubic inches of your motor .Also allows you to adjust flow on another port when at cruise speed.Really made a difference in the engine.The guy at wagner is very knowledgeable about crank case ventilation systems
 
Wagner is the company that makes the pcv valve.Just google adjustable pcv valve and there web site will come up
 
Many are gonna ***** about the price but I think thats one of the best products Ive heard about in years.
 
Right now I'm running the original set up, which is the PCV valve coming out of the passenger side valve cover, and it is connected to a vacuum port on the carb. The driver side valve cover has a baffled breather valve which is just open to the air right now, but was originally tied into a nipple coming off the air cleaner.
 
hmmm my PCV sits in the driverside valve cover... and the airfilter is connected to the passenger side VC . The snorkel of the air cleaner shows to the drivers side...

the engine is a 340 cui also..

Greetings Juergen
 
It doesn't care which side it's on. As long as the fumes come out one side and the clean air goes in the other side. You need some kind of filter on the inlet, whether it's a small K&N type, or it draws from the inside of the air filter, the way the OEM did it (usually).
 
Just for the record.... if the Wagner valve is too expensive for you, then know that there are different transition vacuum levels (the vacuum level below which full PCV flow opens up for cruise) in different PCV.s The stock metal Mopar PCV tends to open to full cruise flow at somewhere in the 14-16 in range.... which means that for even mild cams the flow will be wide open at idle, which makes idle tuning more difficult. PCV valves like the FV191 and FV184 open to full cruise air flow at lower vacuum levels, meaning that they will be properly closed down to the lower idle flow level at the vacuum levels found in mild street engines.
 
The Fram FV191 seems to work good on my 340 with a Comp Magnum Muscle 268AH-10 cam (268°I/276°E, .464” lift).
 
a friend of mine, who has held a nhra stock record, 18 times in the past, has told me he is setting up dual pcv valves on about everything now. I`m thinking of doing it, or running a breather line off the opposite cover from the pvc cover, in to the breather. had my hot 406 sbc set up that way. if I remember right my 68 426 st hemi was set up that way from the factory also. food for thot .
 
nm9stheham said:
Just for the record.... if the Wagner valve is too expensive for you, then know that there are different transition vacuum levels (the vacuum level below which full PCV flow opens up for cruise) in different PCV.s The stock metal Mopar PCV tends to open to full cruise flow at somewhere in the 14-16 in range.... which means that for even mild cams the flow will be wide open at idle, which makes idle tuning more difficult. PCV valves like the FV191 and FV184 open to full cruise air flow at lower vacuum levels, meaning that they will be properly closed down to the lower idle flow level at the vacuum levels found in mild street engines.
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Please tell me more! I just started another thread on the problems I am having getting a consistent idle! The exact problem you mention. I'd love to know if a PCV upgrade could fix this.
 
famous bob said:
a friend of mine, who has held a nhra stock record, 18 times in the past, has told me he is setting up dual pcv valves on about everything now. I`m thinking of doing it, or running a breather line off the opposite cover from the pvc cover, in to the breather. had my hot 406 sbc set up that way. if I remember right my 68 426 st hemi was set up that way from the factory also. food for thot .
Click to expand...
So you set up a second PCV on the breather side? And run it through one of the unaccounted for ports on the carb?
 
Well we had lower vacuum and inconsistent idling on a 340 with a Z-268-2 Crane cam, and replaced the stock Mopar metal bodied PCV with a NOS one, and it did the exact same thing. In pulling the PCV off the valve cover with the hose still attached, I could tell that the PCV was sucking a lot more air than normal at idle, even at 12-14 inches of vaccum. That is the point at which I started looking at other PCV's and read up on-line. I picked up an FV191 because it met all the requirements for opening to the higher cruise flow at a lower vacuum level, and was cheap and local. Put it in with some modified mounting, and voila! lower air flow at idle, and better idle vacuum and idle stability.

The PCV's that open to cruise flow at lower vacuum levels are easy to find if you look for GM cars in the 70's-80's with mild cams in them from the factory. I can teel you that the FV191 stays closed down to the lower idle air flow level at 12 inches of manifold vacuum but I have not tested the exact vacuum level at which it opens up.
 
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