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Looking for help with ls3 catch can/pcv routing.
I’m ls swapping a 350z, and would like some input on the best solution.
I’ve got ports on both valve covers, valley cover, and one on both side of the intake manifold behind the throttle body.
Previous owner of the engine had a catch can with two inlets and one outlet with a check valve on it.
He had one inlet tied to the passenger side valve cover, the other to the valley cover, and the outlet to the intake on the passenger side.
Then he just had the drivers side valve cover and intake manifold tied together.
Is there a better way?
From my research it looks like the valve covers Instead need to be tied into a fresh air port after the maf on the intake tube. Then the valley cover to the catch can and then to the Intake. Then that leaves the drivers side of the intake manifold open, in that situation. Best to cap it and if so with what?
Or is there a better way to route everything?
Heres what you're looking for. Put the catch can (unvented) on the blue line between the valley cover PCV and the intake. Cap any other ports on the intake as they will just be vacuum leaks. I'd use the stock valley cover as the PCV is well baffled. I prefer the Radium Engineering catch can as its simple, clean, easy to empty, and includes a dip stick to check the volume of fluid as it accumulates.
The vacuum port on the driver side of the intake was originally used for the EVAP system so if your not using that and have it disabled in the tune then you can just cap it off. Nothing wrong with using that side for PCV and capping the passenger side off if that works better. You can route it as shown above and just install the can between the valley and the intake manifold.
The vacuum port on the driver side of the intake was originally used for the EVAP system so if your not using that and have it disabled in the tune then you can just cap it off. Nothing wrong with using that side for PCV and capping the passenger side off if that works better. You can route it as shown above and just install the can between the valley and the intake manifold.
the valve covers need to be vented in between the throttle body and the maf correct?
Wouldn’t want to tie those into where the stock evap went right?
The valve covers simply need a source of filtered fresh air....which could be as simple as a valve cover breather with a filter element.
The crank case, needs to see vacuum. Typically, this involves a baffled PCV valve connected to the intake or a vacuum port in order to ensure the crank case is seeing vacuum without sucking oil into the intake. If you want to be sure no oil enters the intake, a catch can can be added to this line.
PCV is for emission controlled vehicles so let's just agree to disagree about this so called fresh air the crankcase needs. If it makes you feel better seeing some engine oil in a can then by all means install one and enjoy.
Sorry, youre fundamentally wrong. The crank case needs to see vacuum....it aids in ring sealing and prevents, or minimizes blow by. Go ahead and cap the valve covers as well as the valley cover....let me know how that works out for you....
Even first generation small block Chevy's had a PCV system of sorts....the valley was vented to the intake and the crank case had a draft tube.
If you dont run a PCV, you'll see significant oil transiting past the rings and burning in the combustion chamber....not to mention the pressure build up in the crank case with will push oil vapor past all of the seals in the motor, eventually coating the engine and engine bay in a film of oil.
Sorry, youre fundamentally wrong. The crank case needs to see vacuum....it aids in ring sealing and prevents, or minimizes blow by. Go ahead and cap the valve covers as well as the valley cover....let me know how that works out for you....
It doesn't need to see vacuum but has to be vented. The PCV system only works under part throttle and idle, It does nothing under load because there is no vacuum at the source at that point.
It does nothing for ring seal or blowby.
The PCV system only works under part throttle and idle
That's actually the upside of the whole thing though. Vacuum is your friend for 99% of driving. Better than no PCV.
Originally Posted by LLLosingit
It does nothing under load because there is no vacuum at the source at that point.
And that's the downside of the whole thing. Would be better with vacuum on the crankcase, but probably not worth fretting about unless you see a problem. Most of us aren't pushing our cars hard enough to matter. And it's really quick and easy to reconfigure PCV for the track if you want.
the valve covers need to be vented in between the throttle body and the maf correct?
I would suspect the stock layout has clean air inlet being tapped off the air intake after the MAF because the air mass has to be counted in a closed system. In other words, what goes in the valve cover on the clean side also goes out to the manifold on the dirty side and is factored into the engine air mass calculations. Also, it keeps the MAF sensor cleaner when oil and vapors spew out the valve cover under WOT.
Speed density tunes don't need to worry about this stuff.
I find it hilarious that people insist on using the intake manifold to pull air through the crankcase in order to have the effects of blow-by go back into their engine combustion chambers. Is it cleaner for the environment? Yes because the catalyst acts as a filter to slow the emission of these byproducts of combustion but it damn sure isn't any cleaner for the inside of your engine and exhaust components. If crankcase pressure was so bad on my engines then I'd have my dipstick blowing out of the hole, leaks from the covers and oil on my spark plugs due to excessive blow-by getting past the rings. Well this certainly isn't the case so I'll end with a thanks but no thanks and continue to trust what I know about the effects of PCV and find another way of dealing with blow-by which is to vent the valve covers to atmosphere and call it a day.
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Last edited by 01CamaroSSTx; Jun 7, 2021 at 12:49 PM.
I find it hilarious that people insist on using the intake manifold to pull air through the crankcase in order to have the effects of blow-by go back into their engine combustion chambers. Is it cleaner for the environment? Yes because the catalyst acts as a filter to slow the emission of these byproducts of combustion but it damn sure isn't any cleaner for the inside of your engine and exhaust components.
The PCV system will keep the inside of the engine cleaner as in crankcase/valve covers and your oil will last longer, How much depends on the environment the car is operated in. The byproduct of combustion is pretty nasty and some does end up in the crankcase/valve covers and oil. If you run your engine long enough and change the oil often enough then it's not a problem. The downside is as you said, It comes at the expense of valve deposits and contaminated combustion cycle but cam choice can also cause the same issue with reverberation.
Hell even the fuel you use can have an impact, E85 is hydroscopic and your burning it at higher volume and usually at a lower temperature so you either need to bring the engine fully up to temperature every time you start it or you should probably run a PCV system.
I run E85 in my S10 with a PVC but it was meant to be driven daily, On the other hand my Son in-law runs his just vented but it's not driven as often and get oil changes more often.
As a side note, I started an engine on the run stand a few times when the temp inside the garage was in the 50's and it didn't get fully warmed up every time and it milked the oil, Had I had a PCV system running it would not have and it would have saved the trouble of flushing the engine a couple times to get it all out.
Replying to post #5, since the crankcase vapors are going into the intake manifold to be burned, on a MAF tuned system the MAF needs to see the air flowing into the crankcase. So a simple filter on a valve cover for an air inlet isn't a correct configuration.
Replying to post #5, since the crankcase vapors are going into the intake manifold to be burned, on a MAF tuned system the MAF needs to see the air flowing into the crankcase. So a simple filter on a valve cover for an air inlet isn't a correct configuration.
How do you figure? The vacuum source is on the intake itself so the MAF would never see how much air is flowing through it, They use either a PCV valve or in the case of the LS6 it has a restriction at the valley cover to regulate airflow and that is compensated for in the factory tune.
If it were that simple, The reason I have been told the clean air is pulled after the MAF is the fact that by pulling it after the MAF means only clean air passing over the MAF. If you pulled fresh air before the MAF then blowby under throttle would pass over the MAF and not only shorten it's life but would also skew the reading.
The amount of air going into the intake from the the PCV is a predetermined number that is a programmed offset in the ECU and only under vacuum, If what you are saying were true then how does the ECU know how much blowby is being pushed into the intake as the engine wears and the amount changes over time....it's being pushed past the rings and the ECU has no way of measuring it.
I've ran them that way and never changed the tune and never had any issues of any kind and yes it was a stock tune, I prefer not having excess crankcase pressure running through the intake underload, It does nothing but contaminate the incoming charge.
Last edited by LLLosingit; Jun 9, 2021 at 09:45 PM.
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Ls3 swap catch can/pcv questions 
