You Sir have my gears turning.. I've thought it through, and I can't see a down-side to installing a PCV valve (in the appropriate direction of flow of course) between the TB and the valve cover.

I will use a short section of clear tubing between the TB and PCV to provide monitoring of potential oil flowing back into the TB, report my results later this weekend.

 

I have thought of this ..... but in essence you would be preventing pressure from escaping when it is most necessary.


DH

 

I believe the standard PCV valve would un-seat before blowing any seals.

 

Yeah, using a PCV valve in the right direction might do the trick. That way the valve would be sensitive enough (key here for it to work right) to flow fresh make-up air into the engine, but would become pretty restrictive to dirty any crankcase fumes trying to flow backwards in to the TB/intake duct under WOT, high RPM conditions.

Yeah, this could be a good mod if it works as thought. Let us know if you test this mod out!

 

But if you have the dirty fumes going out of the engine through the normal PCV route, then the engine guts can't build up any pressure. If the pressure goes down slightly in the crankcase from the intake manifold vacuum, then the PCV valve in the fresh air tube will open up and allow more fresh air into the engine. PCV valves have super soft springs in them, so it doesn't take much pressure delta across them to make the valve operate and flow.

The way a spring loaded PCV valve operates, there would have to be a lot of positive back pressure from the crankcase (like a backfire) on the valve to make it close completely -- that would virtually be impossible unless the dirty vapor route was completely plugged or there was some insane amount of ring blow-by going on where the normal dirty vapor flow couldn't keep up. Even under those conditions I don't think a PCV valve has an air tight seal.

I don't think having a PVC valve (used as a "check valve") in the fresh air line will cause any pressure build-up at all. It should create enough resistance to backflow so it will cause most of the dirty vapors to flow through the normal PCV & Catch Can route to the intake where it's supposed to go.

 

Dan and Zee

I hope you guys are right. I have check valves but did not use them for this idea because on my last motor when I just plugged the valve cover nipple I would hear squeaking noises (seals ??) and I assumed the check valves would give the same result. But maybe the PCV valve will give the desired results without any downside. Just keep your ears open for the squeaking noise.......


DH

 

Hey Dan, I was thinking about the way the PCV system works and have an idea ... see what you think.

Why not just relocate the OEM PCV valve into the fresh make-up air hose, in the proper direction for flow from TB to engine to intake manifold? This means there would be no PCV valve between the engine and intake manifold -- only the oil catch can. If you think about it, why would you need two PCV valves in series by adding one to the fresh air line in conjunction with the OEM location.

If there was just one PCV valve in the fresh air line, then it would essentially regulate the flow through the engine (like in the OEM location), but it would also force the crankcase vapors to be sucked out through the intake manifold under WOT/high RPM conditions ... thereby eliminating any backflow to the intake duct under WOT.

Let me know what you (or anyone else who's into PCV system analysis) think. Maybe someone has already tried this ... but I don't recall reading about anyone doing it this way. Might be worth starting a new thread on this idea if it has any merit.

 

I believe there are a few issues with your idea, idle quality being one of them. I'm not going to venture that far out at this point; the core PCV system design we have hasn't changed significantly in the last 25+ years, I'm not quite ready to re-invent the wheel.

 

I don't see how there could be anything that would cause any engine performance issues. If you think about it, having a PCV valve anywhere in the same series flow path will affect the flow the same way.

The only thing I could see possibly detrimental by moving the PCV valve location to the fresh air line is if there was a major backfire then there wouldn't be anything stopping it from potentially going into the crankcase. There are some guys who don't run a PCV valve at all, so they would have the same risk in the backfire department.

So it looks like just adding another PCV valve to the fresh air line might be a safer way to go.

 

O.k., so I went to the local Pep Boys, went through all of the PCV valves they had on display. First off, all PCV valves are not created equal; some had springs that seemed to do "nothing", others had stiffer springs that would more or less hold the valve closed w/o vacuum.

When I pulled the stock TB to valve cover hose, I noticed it was bone dry inside (34,000 miles, a few track days, many mountain runs).

I installed the new PCV in the proper direction. I had an assistant rev the motor several times, and although I could hear and feel the stock PCV valve open and close (as expected), the new PCV valve did "nothing". I also tried closing the hose on the new PCV valve, again, no response.

I then decided to remove the new PCV valve, re-install a new hose with the last 1/2" fitted with clear tubing. The reasoning here is if ANY oil mist or fluid passes through the breather line, I'd see it in the tubing.

A friend and I went on a 4 hour mountain run (details edited on behalf of sensitive audiences). These runs are as close to a track-day simulation as is possible w/o actually going to the track.

The result; absolutely no trace of oil passing through the breather line.

In contrast, my E.E. can in the "reverse hose" configuration picked up a significant amount of oil; thank goodness this oil is no longer making it into the intake manifold! The stock GM PCV configuration is certainly inadequate. Every single LS1 should have a catch-can installed, no question.

To summarize my experience; I do not believe installing a second PCV valve in the breather line has any value. I do not believe there are significant forces at work (either pressure or vacuum) to actuate the valve.

Obviously others have witnessed oil in this line, so they should utilize whatever methods available to counter oil intake. Poor ring sealing? Excessive crankcase pressure? Very long, sweeping high-G force right hand turns? What I do know is the motor in my car operated in the most severe conditions it will see for 95% of its life does not currently require any additional measures to counter oil intake via the breather line.

Howie is out there in Cali, running at Willows. I've raced there many times on my Superbike (high 28's as a novice before moving to the East coast); turns 8 and 9 are right-handers, so I can't see that being an issue; long left-handers could be problematic.

 

If your fresh air line doesn't have any evidence of oil residue, then there isn't really any concern. I wonder why some guys see oil in this line and others don't.

Could be a number of reasons the new PCV valve didn't seem to actuate. Maybe the spring was too stiff, or maybe fresh air was leaking in from some other path.

I think it was mostly because under a no-load situation (ie, just blipping the throttle in neutral) doesn't cause enough flow through the PCV system. Remember that the whole crankcase is a big reservoir of vapors and in order for the 2nd PCV valve to actuate, the whole guts of the engine would have to be sucked down enough to cause a big enough pressure delta across the valve to cause fresh air to enter the engine. Under WOT high RPM mode it would probably flow.

Good observations and report of your experience. Yes, it seems a 2nd PCV valve doesn't do much if anything, but on the other hand it wasn't actually used in real driving conditions so it's hard to really know, per my comments above.

At any rate, since your fresh make-up air tube stayed bone dry I'd say your motor is pretty tight and I agree that guys who see oil residue in the fresh make-up air line have other issues, like too high oil level and/or lots of ring blow-by.

Another thing that can cause crankcase vapors to backflow through the fresh air line is a defective PCV valve that doesn't allow proper flow to the intake manifold. If the diry vapor path is too restrictive, then the only other path for the vapors to escape the crankcase is the fresh make-up air line -- mostly during WOT & high RPMs conditions.

 

All this info is great! You guys have added some very valuable information to this. Now others can get some valuable information about the function of the catch can in addition to helpful installation tips. Thanks for making this a great post.

 

Dan

Try a $3 PepBoy paper feul filter. It may trap vapor that your clear hose is difficult to see.

If you are not having oil in the vent to TB line great for you

But I had it in my H/C LS1 and in my current H/C 402. Obviously it is much more significant at the track.

I have done my share of canyon runs. And they only provide a fraction of the track abuse.

WSIR turns 2,8, and 9 are high-G and RIGHT handers!!!! But your point is the oil should be leaning to the left.


DH

 

Chrimney, I fixed my post, momentary lapse of reason!

 

Missed this post - nice install, Jason

 

Good info here..........here's a couple pics of mine..........all in all.... a better designed bracket would keep bottom of the can from contacting hoses.

 

I used the hose that was included to attach from the PCV to the top of can and purchased an extra piece for the short run from the can to the intake.

 

An new bracket is under development.

 

I will be ordering one the soon as that happens...

I assume Elite (or you) will make it known here.


DH