L- 6 PCV system revisited

[Jeff Balazs]

Hi Guy's;

I had put together a PCV system for my truck based on parts available from VPW. In getting the truck running properly I had to abandon the system in order to get some idling issues sorted out. I believe this problem was caused by the use of a used PCV valve which does not operate correctly.

 

I would really like to refit this system as I have no doubt as to the benefits of a system like this over a road draft tube when it is operating correctly. Most of my driving will be short trips of 10 to 15 minutes in duration in stop and go conditions and this is where a PCV systems really shows it's stuff. Since this is going to be my daily driver I am particularly interested in preventitive measures like this.

 

Has anyone out there come across a modern properly sized PCV valve for this application?

If so what have you used?

 

The valves which VPW offer are used threaded metal housing units which fit well with the piping but did not seem to function properly. Not certain if the problem is wear related or if it is a sizing issue but with it in place it caused enough of a vacuum issue to effect the idle.

 

Thanks, Jeff

[JBNeal]

the carburetor will need adjustment with the addition of the PCV system as this is introducing a controlled vacuum leak into the intake charged air.  There are two parts to the system:  the PCV valve plumbed from the crankcase to the intake manifold, which draws vapor at low rpm; and the draw line plumbed from the oil filler pipe to the air cleaner base, which draws vapor at high rpm.  The original PCV kit that was documented had among its parts listed a replacement idle orifice tube with no specifications listed.  This has led to speculation that this tube allowed more fuel into the carb to compensate for the added air allowed into the charged air stream.

 

grey beard installed his VPW PCV valve but had some trouble so he replaced it with a modern valve.  He did some stewin' on the problem & was able to remedy the VPW PCV valve problem with some careful machining.

[cavisco1]

I seem to recall someone using the PCV valve from a 3.0L Mitsubishi engine. I believe that one is metal and threaded on one end.

 

Scott.

[MBF]

I used one from a MoPar slant six.  Wipers still work fine, but my wolf whistle is weaker sounding due to the reduced residual vacuum.  Mike

[Jeff Balazs]

Thanks Brian;

I saw in the links you posted where GB drilled out the main jet. I will have to see about getting a spare jet before attempting this. I wonder how hard these will be to find? Or if you can even get these in various sizes?  I suppose one of the Carb specialist outfits must have spec's and sizing info. My truck is a fluid drive with a DTG1 Carter and has a later 230 in it so I need to make certain it is jetted correctly anyway. God only know's if this was ever properly addressed by the PO.

 

Mike, That's funny.........does it sound like a coyote whistle now?

I have electric wipers so nothing but vacuum advance on the system at the moment.

 

Thanks, Jeff

[De Soto Frank]

My '41 De Soto is equipped with factory PCV.   The road draft tube is replaced by a pot-metal cap / valve,  with 5/16" steel tubing that wraps up around the rear of the manifolds, and attaches to teh intake via a "double-wide" junction block that taps into the intake manifold right below the carb mounting, utilizing the same tapping originally intended for the vacuum wiper connection.

 

Nothing special on the oil filler / breather cap - no additional plumbing to the air cleaner, etc.

 

I don't think this system works very well, and some years ago, I planned to sneak a modern PCV into the OEM plumbing back behind / under the manifold.   The PCV valve I sourced was threaded on one end ( 1/8" NPT ?) and had a 5/16" hose barb on the other end... I think it was for a 1970's or early '80's Buick ?   That was 14 years ago, and I never did follow-through on this.

 

All that said, I think a PCV system with a modern (1960's or later) valve and plumbing can only help, especially for a vehicle that sees lots of short-trip oepration.  

 

The good old "road draft tube" is at its best out on the open road, at speed.

[Young Ed]

Thanks Brian;

I saw in the links you posted where GB drilled out the main jet. I will have to see about getting a spare jet before attempting this. I wonder how hard these will be to find? Or if you can even get these in various sizes?  I suppose one of the Carb specialist outfits must have spec's and sizing info. My truck is a fluid drive with a DTG1 Carter and has a later 230 in it so I need to make certain it is jetted correctly anyway. God only know's if this was ever properly addressed by the PO.

 

Mike, That's funny.........does it sound like a coyote whistle now?

I have electric wipers so nothing but vacuum advance on the system at the moment.

 

Thanks, Jeff

 

 

Jeff I've got parts carbs. I'm also not sure if there are various sizes or if they are marked....

[Jeff Balazs]

Hi Ed;

I may take you up on this. Kind of depends on what I can find out about these jets. I suspect that there was different jets and tuning data available at one time.....but wether any of it still exists remains to be seen. Trying to get a retrofit system like this working properly without knowing that you have all the right stuff is probably just asking for problems. To me there is no doubt that a properly working PCV system would be of great benefit in keeping the oil clean and uncontaminated. But it has to work correctly and so far I don't have enough info to make me feel like this is going to be successful.

 

I will probably drive it the way it is for a while so that I can assess how close the carburation is set up to what it should be in the first place. It is possible that this carb has the correct jets in it for a PCV system as there was one of sorts cobbled in when I got it.....then again it was all wrong so who know's?

 

Jeff

[MBF]

You may be able to richen up the idle circuit just by opening the mixture screw.  I was more concerned about it running too lean at highway speeds, but its been 4-5 yrs and the plugs still show the correct color.  It will definitley keep your oil cleaner and reduce sludge buildup especially if you run it long enough to get the oil up to a temp where the moisture will vaporize and get run through the PCV system.  Short runs won't change things much.  You'll still get a condensation buildup in the crankcase but if it isn't getting the oil hot enough to remove it it won't do much good.  Mike