Fixed orifice PCV valves and high rpm cams

[unclewill]

My 482 used oil.  Lots of oil.  Stupid amounts of oil.  Like a quart every 70 miles!  No smoke, no leaks, but always a quart or two low it seemed.  I changed the intake gaskets, I changed the pcv valve, put a baffle in the valve cover.  Nothing worked.  I thought maybe the rings didn’t seat or the valve guides were bad but either of those scenarios meant pulling the engine and starting over and the symptoms just didn’t add up.  I still suspected the pcv.
One day while researching alternative pcv valves, I read the online instructions for a very expensive adjustable pcv valve:
 http://mewagner.com/?p=444
The guys at Wagner did their research on pcv systems in developing their product and concluded that, first, off the shelf pcv valves are basically junk, poorly calibrated generic replacements for items specifically tuned by the OEMs, and second, there are two scenarios for a pcv valve related to engine idle vacuum.  Stock and lightly modified engines produce vacuum >7 inHg at idle.  High rpm cams with big overlap produce <7 inHg at idle.  For the second scenario they recommend running their pcv valve in “fixed orifice” mode.
So GM had a problem with some LS engines burning lots of oil a few years back.  Their solution was also a fixed orifice pcv valve.  Autozone sells p/n PCV1009DL which is the GM replacement part for 99 cents!  It looks like a pcv valve but hollow with a single hole for air flow.  Buy a handful of them then drill and swap to suit your engine.
But pcv valves serve a second function as well.  They prevent backfires from igniting gasses in the crankcase by acting as a check valve.  So any fixed orifice pcv must have a baffle to prevent this.  Part number BF618DL + a little fabrication worked in my case.
What does all this mean?  Well, my engine pulls 6-7 inHg at idle, then 15-19 inHg at cruise (big displacement+high rpm+nearly closed throttle).  This sends all the wrong signals to a “stock” pcv valve resulting in a buildup of crankcase pressure when that pcv closes at high vacuum/high rpm cruise.  The oil is then forced wherever it can go - out the seals, back through the breather, past the rings, but most likely into the intake stream through gaskets or valve guides since that is where the greatest pressure/vacuum gradient is.  Hence the high oil consumption.
The fixed orifice pcv is like a permanent vacuum leak with flow that varies slightly with changing vacuum levels.  Here is the equation:
https://www.tlv.com/global/US/calculator/air-flow-rate-through-orifice.html
The trick is to use the largest orifice you can without disrupting your idle.  I drilled mine to 0.109” (7/64).  This way I get max flow at high vacuum therefore relieving the pressure in the crankcase and eliminating excessive oil consumption.
One caveat:  a carburetor will likely need jetting to prevent lean conditions when you start monkeying around with downstream air flow.  My self learning efi automatically corrects for this making it easy.
The takeaway from all of this rambling is that an improperly tuned pcv system can have profound effects on an engine and high lift big overlap cams are not always compatible with generic pcv valves.  A fixed orifice pcv valve or pill may be the best solution when dealing with pcv problems, even if it’s just used as a baseline.
Please weigh in on this topic as I am no expert, but it did work for me! 

[6667fan]

It is awesome that you have sussed out the solution to your oil consumption. I feel that the caveat regarding your fuel delivery system, (EFI). is important. Tuning out the developed lean condition via carb(s) is a significant hoop to jump through. I have the Wagner PCV on a 482 and the cam necessitated running it in the fixed position. I was (fortunate) and did not experience the oil consumption though I have been down that path with Print-O-Leaks.
JB

[machoneman]

My old post on a Boss 302 valve......
 
August 26, 2017, 07:15:30 AM »

Get a PCV valve for a Boss 302! I've fooled with this issue a lot and the Boss unit has the lowest spring tension and has worked well on many a hot-rodded engine that users have tried it on.

[e philpott]

GM's partial fix is a new Valve cover with the PCV relocated and it does fix the vehicles that suck oil through the old location   , but in most cases after that your back to Piston Rings on the GM vehicles and it's not just limited to LS's on the Ring problems , glad it worked out in your case though

[jayb]

My fix is to not use a PCV valve.  I don't like them because they will deliver an oil mist into the intake manifold that makes the air/fuel charge more prone to detonation.  I either use plain breathers, or else a Moroso crankcase evacuation system.  If you use plain breathers and have an issue of oil mist coming out, a remote breather can is a great solution; any oil that shows up there  can easily be drained out, and won't come out the breather at the top of the can.

[1968galaxie]

I also do not use a PCV valve. Just one breather on each valve cover.
No oil dripping from breathers.
I certainly do not want oil contamination in the intake manifold ever - idling or wot.

Cheers

[67428GT500]

My cam profile isn't that radial. 232, 240@.50. However, I did notice oil on the bottom of the plenum on my C7ZX dual quad intake. I know most 1967 Shelbys ran the PCV vavle to the bottom of the air cleaner assembly. Mine is ran to the rear vacuum port on the right side of the intake.
Should I restrict the vacuum to the PCV to stop the oil in the intake? Or should I be looking at another culpret?

                                                                                         -Keith

[cjshaker]

My fix is to not use a PCV valve.  I don't like them because they will deliver an oil mist into the intake manifold that makes the air/fuel charge more prone to detonation. 

I agree with Jay. Even new vehicles are having issues with this, including the newer Ecoboost engines (a well known issue, compounded by boost and blowby). There is another solution if you feel you need a PCV...use a catch can. It'll separate the oil mist before directing it back into the engine. It really should be the first upgrade on any new car with any performance potential. Might not be the prettiest addition to an FE engine, but they work. They do need to be emptied on a regular basis though. They can be found on any performance automotive site, especially ones aimed at the newer performance car crowd.

[jayb]

My cam profile isn't that radial. 232, 240@.50. However, I did notice oil on the bottom of the plenum on my C7ZX dual quad intake. I know most 1967 Shelbys ran the PCV vavle to the bottom of the air cleaner assembly. Mine is ran to the rear vacuum port on the right side of the intake.
Should I restrict the vacuum to the PCV to stop the oil in the intake? Or should I be looking at another culpret?

                                                                                         -Keith

I think I'd remove the PCV valve and replace it with a breather, then run it for a while and see if the oil issue disappears.  If it does, you have the culprit.  If it doesn't, you are probably looking at a leaking intake gasket.

[Tommy-T]

I ran a fixed orfice set-up off of a Volvo for many years on my '56 T-Bird. It worked fine. One small vacuum line to manifold vacuum, the large hose to the air cleaner. There is a small oil "trap" in the orfice where it plugs into the intake manifold. I never had oil residue in my air cleaner. Also, unplugging the orfice from the intake manifold was used for the oil fill.

The reason I ran it was that I wanted to run Thunderbird valve covers with no holes in them, and I was running a Streetmaster intake with no provision for an oil tube. The oil tubes in the front of the manifold are ugly anyways.
 

[66FAIRLANE]

I was using a fixed orifice one I made with my efi for consistency.

[unclewill]

With regard to catch cans:  if the engine has oil consumption problems through the PCV, the catch can will collect the oil, but it is now removed from the crankcase.  This is why I chose an inline baffle with the capability to drain back. 

[Dumpling]

Could you plumb a catch can to an accusump to keep the can empty?

[cjshaker]

Could you plumb a catch can to an accusump to keep the can empty?

I don't see how, because the accusump is always under pressure.

With regard to catch cans:  if the engine has oil consumption problems through the PCV, the catch can will collect the oil, but it is now removed from the crankcase.  This is why I chose an inline baffle with the capability to drain back. 

I'd just say, if you are removing enough oil to affect the level in your pan, you have bigger issues..lol

[unclewill]

I'd just say, if you are removing enough oil to affect the level in your pan, you have bigger issues..lol

A malfunctioning pcv system has the ability to drain the pan in a couple hundred miles under the right circumstances.  I still can’t believe how much oil it can consume!  You are right, though, it’s better to fix the problem than to rely on a baffle or catch can for anything more than trivial amounts of engine oil.