PCV & catch can routing question (why plug the rear passenger side valve cover?)
03-25-2014, 02:30 PM
#1
PCV & catch can routing question (why plug the rear passenger side valve cover?) I am installing a RX performance dual valve catch can (designed for forced induction) on my naturally aspirated 2001 LS1. I have the LS1 valley cover with one fitting on the rear of the drivers side valve cover, and 2 fittings on the passenger side valve cover. The stock PCV routing is show here:
I have done quite a bit of research in the thread https://ls1tech.com/forums/generatio...ing-ok-11.html but have one question; why do some recommend capping off the rear passenger side valve cover, where others leave it spliced into the line that goes to the rear of the drivers side valve cover?
In my correspondence with RX and 405HP_Z06’s original diagrams in the thread I mentioned above, it seems that it is recommended to cap the rear of the passenger side valve cover as in these diagrams:
405HP_Z06 diagram:
RX diagram:
However later in the “my catch can routing ok” thread 405HP_Z06 says it is ok to leave it spliced in to the line like it runs from the factory, but does not say why. Note that this is also the way that the Elite Engineering and Sakiou Michi instructions show to route the system.
Elite Engineering diagram:
Sakiou Michi diagram:
405HP_Z06 also posted a flow diagram of the PCV system. To me the flow path looks like it would be trapping dirty vapors inside of the passenger side valve cover if you capped off the rear fitting.
So with all that said, here is my proposed routing. I like this idea because It would be much easier to leave it like this (stock routing) as the rear of the valve covers are very hard to access since they are buried under the cowl of the car. However I want to do it “right” not just take the easy route.
So really to get right down to it, why would you plug the rear passenger side valve cover?
I have done quite a bit of research in the thread https://ls1tech.com/forums/generatio...ing-ok-11.html but have one question; why do some recommend capping off the rear passenger side valve cover, where others leave it spliced into the line that goes to the rear of the drivers side valve cover?
In my correspondence with RX and 405HP_Z06’s original diagrams in the thread I mentioned above, it seems that it is recommended to cap the rear of the passenger side valve cover as in these diagrams:
405HP_Z06 diagram:
RX diagram:
However later in the “my catch can routing ok” thread 405HP_Z06 says it is ok to leave it spliced in to the line like it runs from the factory, but does not say why. Note that this is also the way that the Elite Engineering and Sakiou Michi instructions show to route the system.
Elite Engineering diagram:
Sakiou Michi diagram:
405HP_Z06 also posted a flow diagram of the PCV system. To me the flow path looks like it would be trapping dirty vapors inside of the passenger side valve cover if you capped off the rear fitting.
So with all that said, here is my proposed routing. I like this idea because It would be much easier to leave it like this (stock routing) as the rear of the valve covers are very hard to access since they are buried under the cowl of the car. However I want to do it “right” not just take the easy route.
So really to get right down to it, why would you plug the rear passenger side valve cover?
03-25-2014, 06:52 PM
#2
If you use the PS rear port, It'll be pulling a lot of the fresh air from the front PS port right back out, without it having much of a chance to displace much of dirty crank case vapors. Now with it capped the fresh air will be pulled down through the crank case and then out the DS rear valve cover port. This will allow a lot more of the dirty crankcase vapors to be pulled for the engine. Hopefully this makes sense.
Last edited by 99Bluz28; 03-25-2014 at 06:57 PM.
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Homer_Simpson (09-14-2023)
03-26-2014, 11:32 AM
#3
Ok, that does make sense. So basically it is "ok" to leave it like the stock routing (rear passenger spliced into the drivers side), but for better protection the rear passenger port should be blocked off.
It seems that most aftermarket (and GMPP) valve covers do not have a rear passenger side port, which makes sense based on what you are saying. However it seems odd that GM would have ever put the rear passenger port on the factory valve covers (but they have made mistakes before).
It seems that most aftermarket (and GMPP) valve covers do not have a rear passenger side port, which makes sense based on what you are saying. However it seems odd that GM would have ever put the rear passenger port on the factory valve covers (but they have made mistakes before).
03-26-2014, 03:24 PM
#4
Actually with the PS rear port capped I'd use the DS rear as the fresh air inlet an the PS front as the dirty air outlet since the DS rear would be more likely to suck up oil when used as the only dirty air outlet. I believe that's the reason the factory PCV setup uses the PS rear also as a dirty air outlet, just incase the DS outlet gets a bunch of oil in it the vacuum will pull more from the PS which would the be the path of least resistance, resulting in less oil pulled in through the intake.
Last edited by 99Bluz28; 03-26-2014 at 03:30 PM. Reason: corrections
03-27-2014, 09:21 AM
#7
Right!, Vent the valve covers to a breather can and from the LS6 vally run that hose to a sealed PCV can and out of it to the intake with a LS6/LS1 PCV valve inline and cap off the throttle body port, Done!
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03-27-2014, 05:27 PM
#8
Actually with the PS rear port capped I'd use the DS rear as the fresh air inlet an the PS front as the dirty air outlet since the DS rear would be more likely to suck up oil when used as the only dirty air outlet. I believe that's the reason the factory PCV setup uses the PS rear also as a dirty air outlet, just incase the DS outlet gets a bunch of oil in it the vacuum will pull more from the PS which would the be the path of least resistance, resulting in less oil pulled in through the intake.
Everything I have read recommends not using any breathers, as it lets in unmetered air into a system that is designed to be closed?
04-13-2014, 10:33 AM
#13
If you use the PS rear port, It'll be pulling a lot of the fresh air from the front PS port right back out, without it having much of a chance to displace much of dirty crank case vapors. Now with it capped the fresh air will be pulled down through the crank case and then out the DS rear valve cover port. This will allow a lot more of the dirty crankcase vapors to be pulled for the engine. Hopefully this makes sense.
I recommend plugging the port initially and monitoring intake oiling condition. If the engine exhibits higher than expected crankcase pressure and continued intake oiling, integrate this rear port into the PCV system and continue monitoring.
Hope this helps.
Aaron
04-25-2016, 08:59 PM
#14
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I have blocked the ps rear port and ran ds straight to catch can, then from catch can to intake. And kept the factory routing from TB to ps front port. With that I am experiencing high volume of oil in the catch can. And by high volume I mean half full after 100 miles. Before I changed it it seemed to be normal ls1 oil consumption. Do you think I need to y it back into the ps rear port also.
04-27-2016, 02:33 PM
#15
you have to have a pcv valve in the system, either the 'loose' one if it came with the car like that or a built in one at the driver rear cover or valley. if you do not you are putting an unregulated volume of intake vac on the crankcase.
aside from that, and not because i like rx (lol), but you should always follow what the manufacturer tells you to do. you cannot mix and match random 'internet' install diagrams and catch cans. certainly not without a thorough understanding of the situation, and accepting the risk, it can get you in trouble quick and could be dangerous to your engines health.
aside from that, and not because i like rx (lol), but you should always follow what the manufacturer tells you to do. you cannot mix and match random 'internet' install diagrams and catch cans. certainly not without a thorough understanding of the situation, and accepting the risk, it can get you in trouble quick and could be dangerous to your engines health.
