.....a few thoughts.....

1) This is why I don't particularly like giant catch can reservoirs as a way to avoid emptying it for one year - potentially too much oil and water sitting there for too long.

2) If you are using an actual PCV valve, you need to allow it to be lubricated by the oil, hence, the location of the catch can between the PCV valve and the intake.

3) I'm convinced that almost any catch can will catch more if the air and oil are allowed to cool somewhat. This is one reason why I mount my filters away from the intense heat of the engine. The other reason is that most coalescing filters with metal reservoirs have a maximum operating temperature of 175-180F. You can buy larger versions with 250F temp limits, but they are very expensive.

 

I don't think a regular catch can is going to catch 100% of the oil anyway, so there will always be a slight misting of the PCV valve. This is how my setup in on my 02 Zee. The regular spring loaded PCV is between the catch can and intake manifold. Another good reason to go with the fixed orifice unit is that it needs no lubrication, just in case the catch can kept all oil vapors out of the PCV valve.

 

Vacuum line: Valley to AMW to Watts (with coalescing filter) to Intake manifold. No external PCV valve

Fresh line: passenger valve cover to Elite to Watts (with stone type filter - much higher flow than coalescing) to air brigde (rubber coupler) before LS2 throttle body

Last week I took out the coalescing and put in a stone to equalize the flow. Or so I thought ..... now considering puting in this restrictor in the fresh air line.

AND this excess (completely filling the Elite in 30 minutes) oil in the fresh air line was with track conditions. WOT to 125 and 143, quick decelleration and lots of lateral g-force!!

DH

 

Ok. Sorry I need to clarify. I was refering to a PCV as in an 'added on Valve' (as in an earlier thread where the two valves were compared) not the fact that the 3/8 or so tube coming from the valley cover actually has a smaller orifice at the block side. I realize the need for crankcase ventilation, just seems there is a muttling of discussion here. Vents on top of each valve cover work and did for serveral of our 'muscle car engines' back in the good old days (albeit they were stinky). Fact is newer LS engines perform quite well with the valley-to-intake tube. I used this setup on my L92 and ran a small tube from the passenger side valve cover to the back side of my Halteck air cleaner and this works well. If I drove the car more, a catch can would be a good addition and I would suggest this set up to most folks concerned about the issue.

Lastly, when I was geting my set-up together for my L92 in the '97 vette (which has a different and more elaborate PCV system) I researched this with a couple of GM parts folks (at least one who was very knowledgeable (Paul -internet parts- at Crown Cadillac in NJ) and they will tell you there is no PCV valve in the '07 or '08 6.0-6.2 ltr. Now I know you already have been discussing the orifice at the end of the tube but I am pretty sure it is not referred to as PCV by part name and maybe that is where some of the confussion is (not withstanding that it performs crankcase ventilation). I will get information on the part number if anyone desires.

As for the visual inspection, all I can say it's good to live in southern AZ.

 

I read previous post on the fixed orifice PVC valve's. Thought Id give it a try. Started leaking oil out the rear main. Replaced with stock ball unit, no more rear main leak.

 

DH - sounds like the setup above that the vacuum line (dirty line) is more restrictive than the fresh air line. This will definitely cause backflow down the fresh air line at WOT.

Any testing done with that new setup?

Was the excessive oil flow with the old setup with the coalescing filter in the dirty line? If the dirty line is much more restrictive then the fresh air line, then I can see why there was lots of backflow down the fresh air line at WOT.

The only way to reduce backflow down the fresh air line is to make the dirty line as non-restrictive as possible.

Have you tried just putting a catch can on the dirty line and just the coalescing filter on the fresh air line?

 

That's not good news ... Sounds like too much crankcase pressure. Any other mods on you car?

 

As many can see, there is not a one fix cures all in the PCV system mod world. I've come to the conclusion that guys who track their cars would be better off with an open breather setup, or an independent crankcase evacuation pump. I just don't think you can keep all the oil in the crankcase at WOT with the fresh air line setup. At some point you might with tons of catch cans and filters, but at some point the paths are going to get too choked down or extremely unbalanced, and that's not a good thing either.

Are you talking with no resticting orifice in the line?

From what I understand, all 2004+ LS engines have the 2.5 mm dia flow restrictor built somewhere into the valley cover hose nipple. I don't think the nipple is a wide open 3/8" tube. The external fixed orifice PCV unit with the 2.5 mm dia hole is supposed to emulate the new valley cover setup.

I believe the valley cover p/n for the 2004+ LS engines are different than for 2003 and older LS6 engines for this very reason. 2001 to 2003 LS6 had the external spring loaded PCV valve and no orifice in the valley cover hose nipple. A quick check at the dealer should verify this, but I'm sure the dealer can't tell you why the p/n is different. When the dealer says "There is no PCV valve shown" you can bet he's meaning there is no external PCV valve, and has no idea whatsoever that GM started using a fixed orifice to control the flow through the PCV system.

 

Zee, here's what I found when testing flow through the PCV line:

Flow at 800 rpm: 36 LPM = 1.27 CFM
Flow at 4000 rpm: 37 LPM = 1.31 CFM

As you can see, the flow doesn't skyrocket at higher revs. This is why I doubt that the coalescing filter is to blame. It flows 8 CFM without a problem. Of course, if it gets plugged, it could create some restriction, but I tested one of mine after a thousand miles of hard driving and there was a 0.1 psi pressure drop - hardly anything to worry about IMO. Even after 5000 miles, the filter was flowing freely.

 

Good info Dave, but did you take the coalescing filter out of the PCV line and measure the flow rate in the line at the same RPM conditions to verify any flow rate delta? Naturally, you wouldn’t think there would be any with only a 0.1 psi pressure drop, but that test would be a good check point.

If the PCV line flowed much more without the filter installed then it has unbalanced the system, and if the fresh air line is essentially wide open to flow then it will backflow more at WOT. The relative balancing of the two lines in the system is important IMO.

 

Actually, I wanted to see what kind of flow increase would occur without any added filters, primarily to select the correct capacity filter. Those numbers are from the PCV line, weeks before I bought the first coalescing filter. Typically, there is no need to check flow changes with and without a filter if you check differential pressure across the filter. This was my way of determining whether flow was being restricted (significantly) because of the filter.

 

ZEE and Dave

I use my mouth as the flow meter !!!!!! Place the coalescing filter in the palm of my hand so one end is sealed. Lightly cover other end with my mouth and blow......lightly.

With the stone filter, black with oil, there is no resistance
With the coalescing filter there is major resistance

For normal driving my setup with large can and small can with coalescing is going to catch ALL the oil.

But for track driving (the only real driving ) the setup doesn't keep oil from backing into the fresh air line.

Any testing I do is worthless unless I do it on the track.

There are other setups people are using with vented cans and regulators on the cans that I may need to switch to.
http://forums.corvetteforum.com/show....php?t=1724319


DH

 

I guess I would have done the same flow measurement under the same conditions with the same instrument(s) to verify the filter's effect on flow rate. Kind of like testing a car after mods on the same dyno to get a good delta measurement from the mods. I hear you on the 0.1 psi pressure difference across the filter as being small, but at a small flow rate (1.3 CFM) it could be somewhat significant.

 

Yes, I've basically have come to the conclusion that putting catch cans and filters on the stock PCV system lines probably isn’t going to cut it for heavy track use. I think going with some kind of open breather setup is best for lots of WOT use.

For nominal street driving with some short WOT escapades, the stock setup with a catch can and maybe a filter would probably work for fine for most people.

 

The common rule-of-thumb when it comes to replacing a coalescing filter is that when there is a 10% reduction in pressure, it's time to replace it. At the equivelent of 10 psi, a 1 psi drop is cause for concern. At 0.1 psi, no problemo in my book!

 

I agree with Zee, Howie; racing introduces a whole new set of "rules" and you may very well improve things by switching over before racing - kinda like an added race prep step, if you will.

 

I will probably do something before next track day Jan 25

Any suggestions????


DH

 

I guess they zipped right pass this....

 

That WOULD make me change mine back too. Don't feel bad, I had nothing significant to add either.

 

Howie,

You might want to try this guy's advice: