I have a 2010 LS3 that I'm swapping into a 57 Vette. I have relocated the ignition coils and have billet valve covers to replace the stockers (clone of the blue car). I plan to use the breathers in the attached pictures. The breathers have internal PCV valves ported to the 1/8" nipples.

The best diagram I have found for the LS3 shows one stock valve cover plumbed into the clean side of the PCV system. And a oil catch can on the dirty side.

Questions for the clean side:
1) Are the ports on my finned breather(s) too small if I run 1/4" OD line?
2) Should I plumb only one valve cover with a finned breather/PCV valve to the "clean side," and leave the other valve cover closed like the diagram?
2) When talking about the clean side: Is the "clean side" the air intake, after the MAP sensor and before the throttle body?
3) Will pluming into the clean side change my mixture and cause a lean condition?
4) Should I consider a catch can for the clean side also?

For the dirty side:
5) I will run an oil catch can between the valley port and the intake port as shown in the diagram. Can the catch can be mounted low, along side the oil pan out of sight or does it need to be mounted above the valley port?
6) Would the catch can have a PCV valve also?
7) Suggestions on a good catch can?

 

Yeah, run the clean side AFTER the MAF because the MAF MUST measure ALL air to be ingested by the motor. If this is done correctly there will be no AFR problems

 

For questions 5 thru 7

5) Valley cover has a built in pcv valve, a good sealed catch can will help to reduce the amount of oil being introduced to your intake manifold but it's still getting in which does reduce your octane some . The one I have from Mike Norris works well. I'd say you could run those breathers you have by connecting the 1/8 lines to a T and then tying into the port "If it has one" on your throttle body or the bellow between the MAF and the TB.

 

The clean side to me is the air/fuel mixture making it's way into the combustion chambers. The dirty side is the blow by gases from the combustion process. How the engineers dealt with it was through a PCV system which tries to clean the dirty air "gases/oil vapors" before sending it back into your combustion chambers to be burnt again. I'm not sure it would be good idea to have your catch can relocated down by the pan. I think it would cause such a loss in vacuum my power brakes wouldn't work.

 

Mighty mouse are great cans , contact Dave , knows his LS stuff

https://ls1tech.com/forums/attachmen...1&d=1516667005

 

You cannot route Gen IV valley covers/left valve covers that way as there is a built-in orifice in the covers. It would NOT vent properly at WOT.

I guess that diagram is for earlier Gen III engines.

 

 

Jim,
Did you end up venting both sides (passenger and driver) PCV valves through catch can?
My set up on the LS3 bought a couple of months ago has a tube that connects the front PCV valve on valley cover not valve cover back to the intake, will try to enclose picture. This would need to be disconnected to run the system as in the diagram in the first post in this thread. I will assume, this is what the GM engineers felt was best, and would rather leave it.

What are your thoughts about venting both passenger front PCV valve and drivers side rear PCV via the intake after the MAF?
Thanks, Bill

 

 

Whether it's right or wrong here is what I did.
I connected the drivers side valve cover and the pass side cover to a T.
The pass side already has an oriface in it so I installed an oriface in the line from the drivers side at the T. So both side will have about the same restriction.
The output side of the T goes to a catch can, the can is then connected between the MAF and throttle body.
The '33 isn't finished, have only driven it 4 miles (not registered) so far. It runs fine.

 

Hi, Jim. I don't know if that's a good idea. You didn't mention use of the valley cover PCV tube. If not, then you're basically just venting the engine like old school, and that's not good enough. What you want to do is create air flow through the engine that sweeps the crankcase. Getting it wrong is unhealthy for the engine.

Air moves from high pressure ---> low pressure. The "high" pressure side is atmospheric. The "low" pressure side is inside the intake manifold where pressure is in vacuum (below atmospheric). The intended pathway for LS3 engine is air (at atmospheric pressure) enters the cylinder head valve cover, sweeps through the crankcase, and goes out the valley cover and into the intake manifold (low pressure region). If you don't create that pathway, then it doesn't work. And you want to keep air momentum moving in that pathway by avoiding non-value added paths that churn the air in circles, or diverts air for no good reason, or slows momentum toward the intake manifold.

The air picks up contaminants when it sweeps the crankcase. The "dirty side" is the PCV tube at the outlet of the valley cover. A catch can is used to separate droplets of fluid from the dirty side air before it enters the intake manifold.

Now wide-open-throttle (WOT) condition is different. At WOT there really isn't hardly any appreciable pressure difference between atmosphere and intake manifold, so the momentum of air flow is interrupted. But pressure is building up in the crankcase faster than ever, especially at high engine speed. So what happens is every hole in the engine begins spewing crankcase vapors. Suddenly the "clean side" gets dirty, and that's why sometimes people add a clean side oil separator. If the natural venting of the engine isn't sufficient then people will add a vacuum pump to the crankcase. The vacuum pump re-establishes the desired air flow that sweeps the crankcase to the intake manifold, and it works at all times (unlike relying on manifold vacuum alone).

The PCV system is supposed to be a closed system for emissions reasons, meaning none of the crankcase vapors escape the engine to the atmosphere. All the vapors end up in the intake manifold to be burned by the engine, no matter how those vapors get out of the crankcase. That's why both the clean side and dirty side of the PCV system are coupled to the engine's inlet air tract in one form or another.

 

QwkTrip, thanks for the explanation.
I do have the flex line from the valley pan cover to the manifold connected as shown in w.sims pic in post #9. This is where the catch can should be connected, not where I have it now, right?
Question...
Why not feed clean air into both valve covers? Seems that would do some good for the drivers side too? Yes/no?

 

Jim, QwikTrip,
let me get this straight, you are recommending taking out the aformentioned flex line (that I am assuming the GM engineers devised) and having the catch can in its place, in that way "cleaning" the dirty side prior to re introduction into the intake effectively?
If this is done do you still vent the passenger front PCV and driver rear PCV via the intake after the MAF?, or just the passenger front valve?

 

Yeah, remove the corrugated plastic tube and plumb in the catch can. That's where the dirty air is coming out of the crankcase. The catch can cleans up the air a bit before sending off to the intake manifold.

The LS engine PCV system is not so good (like most factory setups). Each generation of engine (LS1, 2, 3) got a better PCV design along the way. That's why you see different schemas of hose routing and different valley covers and such. The LS3 schema (with the LS3 valley cover) has clean air inlet on the passenger side head, the driver side head is blocked off, and the valley cover has the corrugated tube that goes to the intake. The only reason to modify the schema is if you need to move a lot more air than it's capable of doing.

All the air going into the valve cover is clean air. It doesn't need to be cleaned. However, air and oil mist can come back out and make a real mess, and even get pulled into the engine if the oil dribbles all the way down to the air filter. That's when people use a "clean side oil separator". It basically catches the oil that spits out of the valve cover and holds it until the oil drains back. Daily drivers don't need this. Engines that spend a lot of time at WOT should consider having one. There are choices from mild to wild depending on air flow needs. The LS3 Camaro with 1LE package comes with a clean side separator that screws on in place of the oil fill cap.

 

Just to clarify, everything I said is for a naturally-aspirated engine. You would have to make some other changes for boosted applications since the intake manifold can actually be pressurized.

 

Thanks again for the info, I'll change my plumbing setup.
What's your take on also supplying clean air to the drivers side valve cover?

 

I don't know. Have to get someone else with more experience to weigh in.

 

this was a good thread to read. Appreciate the information. Any thoughts on L99 vs LS3 PCV routing for an NA setup with catch can? I currently have the option to get the valley cover with or without the PCV exit tube. If I continue to exit dirty side out of driver side valve cover and use a cheaper L92 valley cover, is there a negative effect of this versus using the more costly LS3 valley cover exit?

Also, would it be beneficial to do both, essentially pulling dirty side from Driver side valve cover and from an LS3 valley, using a T into the catch can.

 

Think about it this way, you want your oil to drain down from your rockers. You don't want crankcase ventilation going up the pathways that the oil is trying to come down. Clean air in (connected upstream of throttle blade) on the valve cover(s) and dirty air out through the valley (connected to i/m).

 

What’s better for the clean side on a boosted iron block gen 4 application? Running a clean 6AN line from the nipple on an LS3 valley cover to the turbo inlet, or running the clean line from a 6AN bung on the driver side valve cover to the turbo inlet and using a valley cover that has no nipple? Obviously on the dirty side where you run the line from the dirty outlet on the can to the passenger valve cover you’d go bigger than 6AN as you go up in hp. For 1000hp for example you would use the adapter Dave sells which converts the oil cap into a 10AN fitting. (better than running it to a 10AN bung on the driver valve cover) The line running from a “built in” PVC in the can like the one Dave sells goes to the intake manifold and the size can be 6AN.