PCV/Catch Can routing for LS3/L92 C5
 

I'm almost ready to fire up my C5 for the first time after swapping in an L92. Just need to figure out the PCV system. The car will see a fair amount of time on local road courses so I want to install a catch can as well to prevent oil from entering the intake manifold, which was an issue when I ran the car with the old LS1.

The car has an L92 from an '08 Escalade. The valley towers (normally used for VVT) have been plugging with NPT plugs and the engine uses the typical L92 valley cover with the 8 o-rings underneath it as extra security. The valley cover does NOT have the PCV nipple like the LS6 valley cover has.

How should I route my catch can and PCV system?
Do I need a separate external PCV valve?
I want to eliminate any and all oil consumption, especially on track.

This is the rough draft I came up with.

https://farm1.staticflickr.com/944/4...0744bf33_b.jpg

add a check valve...
https://www.mcmaster.com/#plastic-ch...63730bjh2svhcs

Where?

On your drawing, you had a question and arrow pointing to the clean side, on high rev decel vacuum sucking oil back into thru the intake. A check valve will help prevent oil from entering intake on the clean side.

No, don't run a check valve on the clean side of your PCV system!

tl;dr: Doing that could harm your engine by increasing crankcase pressure at WOT.

Full explanation: Since that port should be plumbed to the intake in front of the throttle body (as shown in your diagram) it will never see appreciable vacuum, thus the high rev decel (high vacuum) scenario you mentioned is not a problem. Also, since you didn't mention any kind of forced induction, I think it's safe to assume it will never see any boost either. The green line will almost always be flowing clean filtered air from the intake into the valve cover, to make up for the air sucked out of the crankcase through the PCV orifice by intake vacuum. The only time that flow through the green line may stop, or even reverse (and possibly get oil into your intake) is at WOT, when intake vacuum drops to near zero and blowby can cause crankcase pressure to build. That oily air will need somewhere to go, and flowing backwards through the green line is a much lower restriction path than through the PCV orifice. You could add a catch can on the clean side to keep that oil from reaching your intake, and since you're doing track days, it's probably a good idea. If you put a check valve there though, the only outlet for blowby at WOT would be through the little PCV orifice, which is going to cause crankcase pressure to build up, which is bad news.

Check the barb on the rear of your driver's side valve cover. It should have a fixed orifice in it for PCV. Thus you do not need a PCV valve; it works just like the fixed orifice in the LS6 valley cover. Yes, you should put a catch can on that side too, that's the one that's going to suck oil on high rev decel like you were saying. Good luck!

I am reusing the valve covers from the L92, definitely has a barb on the rear driver's side cover, so I'll inspect to see whether there's an orifice in there. I suspect there should be, and if there is it'll be nice not to have to buy a separate PCV.

Yup, no boost, this is a regular cam'd street motor, stock bottom end and heads minus springs.

Sounds like the ideal setup is 2 catch cans, one on clean and one on dirty side. I'll probably just run without them for the initial start and break in, to get used to the setup, and add them once I've shaken out all the bugs.

Sounds like a good plan! :thumbs:

IMO the ideal setup is not two catch cans.
as much as i do enjoy selling them, i would rather fix a problem with one vs. two.

missing info, what catch can is it you are trying to install? that will answer how it needs to be installed.

How do you remove oil from both the dirty and clean sides with only one catch can? Separate chambers or something?

its all about why the clean side gets dirty, and stopping that from happening.

too much air, too fast blowing out, or too much air, too fast being sucked out.

some of my setups is possible to isolate the clean side from dirty side completely, so there is never any flow (even can be check valved) on that side, so air only enters and never leaves, including any possible oil

Check-valving the clean side or restricting air flow on either side sounds like a recipe for crankcase pressure to me, but maybe I don't fully understand. If what you're talking about is proprietary, that's okay, I don't expect you to reveal trade secrets.

lots of info on the website! www.mightymousesolutions.com

Thanks, now I see what you're talking about. The MM can goes between the crankcase and the PCV valve, so it can provide a lower-restriction path to vent crankcase gases during WOT/boost. Most of the blowby gases should then be flowing into the can and out its breather filter instead of out the clean side, so the clean side should not need its own catch can. I guess that means you could put a check valve on the clean side without hurting anything then too, huh?

Looks like you're using a check valve on the breather filter to make it "exit-only". What's the cracking pressure/back pressure on this check valve? Seems like it would have to be really, really low. Or, maybe it's set up so that intake vacuum sucks it shut? Sorry for hijacking this thread, just curious how this works.

correct on all counts! it is a unique and severe departure from the status-quo and extremely helpful when you get away from what the stock ccv is built for / capable of.

I have a catch can that I was given by a buddy for free as he had no need for it. I'm not dead set on using it if it's not right for my application, but would prefer not to have to buy something else if I don't have to.

http://www.velosterturbo.org/forum/a...d-img_0293.jpg

I did add a small tube inside one of the barbed fittings to extend down about 3" into the catch can, to prevent any "short cycling" that might occur if the fittings were right next to each other in the lid of the can.

any can like that one is better than nothing, but as you can imagine is far less efficient than one with (any sort of) technology going on inside.

that should be used in-line of an existing pcv strategy, either in-line of the fresh air pipe or on the return side (return side is where the daily driving and engine braking oil is) between intake manifold and driver valve cover or valley plate year depending.

Ok, I installed my cheapo catch can according to the diagram in the first post.

-Catch can was filled with stainless steel scouring pads (saw this trick elsewhere on the 'net) to act as a filtering media
-Added a small barbed fitting and 2" length of hose inside the "IN" port to prevent short cycling

Car seems to run the same as before, I will report back with what it "catches" after a week or two.

I'm not as familiar with your valve covers (internal view), but it looks to me like you might want to switch your clean and dirty connections. Usually port on the rear driver's side is a big connection that is wide open. I think that the passenger front PCV port is baffled. A dual can setup is nice, even if the clean side (hopefully) ends up being a visual indicator. I wouldn't try to orifice my own track motor PCV system. It's better, in my opinion to let the vapors vent. If you can monitor what's coming out then you have another tool to keep an eye on the relative health of your setup over time.

Update - I just did a track day with the setup shown in the original post and still had oil consumption issues, though not as bad as it used to be. There was a significant amount of oil being sucked into the duct:

https://farm1.staticflickr.com/839/4...d27bf6d9_z.jpg

The next step is to add another catch can in that line, unless there's a way to prevent the oil from getting sucked through (as Mike mentioned, switch lines since the driver's rear is wide open, and the passenger front is baffled?)

drivers rear does not connect to the air bridge in your diagram.

if you are getting oil from your passenger cover into the air bridge it is from
- too much crankcase flow, blowing oil out with it
- too much vacuum caused by a restrictive or clogged air filter assembly, sucking oil out of it
- an imbalanced oiling system, where there is too much oil sent to the valve-train, usually from increasing oil pump volume without restrictor pushrods

Sorry, I misspoke. The system is plumbed as shown in the first diagram. It's the driver's front valve cover port that leads into the air bridge. No baffles, valves, or catch cans in that line.

You did a track day and didn't invite me? :(

Didn't know you had the C6Z all ready to go! I'll be going again this month once I get this oil consumption figured out.

Another user on the other LS forum suggested this, my concerns are attached

Right - which I think seems to be the best place to connect to the crankcase. However, I am running an L92 valley cover which doesn't have the port on the valley cover. If I decide to try that out I could probably just install an LS6 cover since my DoD bosses are tapped and plugged.

I ordered an air/oil separator that I'll mount (somewhere) and run the valve covers to, using the factory barbed connections, in addition to a catch can that ventilates the crankcase

https://images-na.ssl-images-amazon....L._SL1000_.jpg

Ok, an update, with another setback.

I installed this:

https://images-na.ssl-images-amazon....L._SL1000_.jpg

Behind the driver's fender, on the frame, and ran a 3/8" hose from each valve cover directly to the ports on that air/oil separator to allow the crankcase to breathe.

Nipples on the air duct and intake manifold were capped off to eliminate any change of oil being ingested into the intake during high vacuum situation (high revs, decel, throttle shut).

I ran the car up to 6500rpm in 3rd gear and let off, and am still getting clouds of smoke out the back as oil is consumed. Since the intake tracts are capped there isn't any way for oil to get sucked in, so I'm somewhat stumped on how oil is entering the combustion chamber.

Valve seals are brand new, bottom end (original rings, etc) has about 80,000 miles on it. Thoughts?

may take more than one time to clear out old build up, but if it keeps coming back i would look for the oiliest spark plug and put a new one in, if the oil comes back your work on the engine is not done.

even on the best setups you could have a whisp of oil smoke on severe engine braking like that. oil rings are not perfect seals.

Sounds like I just need to go beat the snot out of it, and get it nice and hot.

I have no problem replacing any components that aren't working properly, but it's frustrating knowing everything except the rings is brand new.

I will take it out this Friday and flog it for a couple hours on the back roads, then throw in new plugs that evening.

Friday night I took the car out with a couple buddies on the back roads and flogged it for a couple hours. Many WOT pulls, lots of high rev no load decel, lots of blue smoke. Never any smoke on WOT, only during the decel from high revs.

Changed out the plugs Saturday morning:

Driver's Side
https://farm1.staticflickr.com/937/2...6933d835_b.jpg

Passenger Side
https://farm2.staticflickr.com/1831/...2e43c51e_b.jpg

They don't look like they have any oil fouling to me, but then again I had a long drive home without any high rev decel which could have "burned them clean". Although, you'd figure they'd have all sorts of residue along the base.

Also worth mentioning is that I drained the air/oil separator immediately after the Friday night beatdown; to my surprise 2 cups of clear water (condensation) came out. No oil whatsoever.