The problem with catch cans and the 350Z
05-27-2012, 01:40 PM
#41
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The plenum is blocked off so no outside air is getting in. If the air in the crankcase leaves the crankcase it does NOTHING to the maf signal at all. You are confused with having a vac leak on the intake side with having open breathers on the crank case.
The crank is producing positive pressure so it will always be pushing gases out and never sucking them back into the crank case. Even if it did suck air into the crank case that air would not be drawn into the intake anyways so it would never cause a problem with maf signal.
thousands of cars have open breathers and it does nothing to the metering at the MAF. Just about every car on the market has a maf and most builds for high hp use open breathers for less crank pressure.
oh, and you didn't look hard enough. Boosted performance makes one as well that bolts onto the front cover of the car to sit right between the 2 timing covers.
05-27-2012, 07:44 PM
#43
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Returned the can I had..bought two new ones w removable tops... used perforated vinyl tubing on the in side of the cans. Bought Poly scrubber's versus the steel .. they look pretty robust. I'm hoping they'd be fine. So two cans for under 70 bucks in parts...500whp set up..anyone know ( not just think ha) of reasons these will not work?
Last edited by bmccann101; 05-27-2012 at 07:48 PM.
05-27-2012, 08:52 PM
#45
You do realize that catch can opened to the atmosphere does NOT interfere with metering?
The plenum is blocked off so no outside air is getting in. If the air in the crankcase leaves the crankcase it does NOTHING to the maf signal at all. You are confused with having a vac leak on the intake side with having open breathers on the crank case.
The crank is producing positive pressure so it will always be pushing gases out and never sucking them back into the crank case. Even if it did suck air into the crank case that air would not be drawn into the intake anyways so it would never cause a problem with maf signal.
thousands of cars have open breathers and it does nothing to the metering at the MAF. Just about every car on the market has a maf and most builds for high hp use open breathers for less crank pressure.
oh, and you didn't look hard enough. Boosted performance makes one as well that bolts onto the front cover of the car to sit right between the 2 timing covers.
The plenum is blocked off so no outside air is getting in. If the air in the crankcase leaves the crankcase it does NOTHING to the maf signal at all. You are confused with having a vac leak on the intake side with having open breathers on the crank case.
The crank is producing positive pressure so it will always be pushing gases out and never sucking them back into the crank case. Even if it did suck air into the crank case that air would not be drawn into the intake anyways so it would never cause a problem with maf signal.
thousands of cars have open breathers and it does nothing to the metering at the MAF. Just about every car on the market has a maf and most builds for high hp use open breathers for less crank pressure.
oh, and you didn't look hard enough. Boosted performance makes one as well that bolts onto the front cover of the car to sit right between the 2 timing covers.
Not sure that's the best baffle system, can't see why pipes come out same side, but at least it's baffled and it was made to fit the 350, so nice
Refer to the post from the LS1 forums a few posts up as to why you don't want to 'open air' the stock closed PCV system.
These systems are designed to work closed, they're not like the old American systems running either draft or open PCV systems.
The air passes the MAF, and some is syphoned off and heads into the crank case. This then gets put through the PCV valve and back into the intake.
If you then have that air no longer going back into the engine, then you're missing air that was metered. It's got nothing to do with outside air getting it, it's all to do with removing air from the system that was metered before it got into it.
It doesn't matter if engines *work* with that setup, they're not working *correctly*
Last edited by F2CMaDMaXX; 05-27-2012 at 08:59 PM.
05-28-2012, 07:08 AM
#48
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the ONLY reason it is designed as a closed system is emissions. That is it 100%. It has nothing to do with performance. In actuality it actually decreases performance because it's burning some vaporized oil which will gum up intakes, valves, and spark plugs.
I've logged and watched the maf signal and tune going from fully closed to an open breather system and it affects metered air zero. The only way metered air is changed is if fresh air is introduced into the intake after the maf. If you have a closed intake system (no pvc attached to it) then nothing is going into the intake. On top of that the crankcase is always pushing air OUT from the catch can not sucking air in. So there is no way for air to actually get back into the intake from the outside.
hook up some vac lines to the catch can and do some logs. It is never pulling fresh air into the crankcase and even if it did the air from the crankcase will not magically get into the intake system unless it's somehow forced up the crankcase and past the piston rings.
I'm not sure how you think fresh air is getting back into the intake from a crankcase breather. It just doesn't make sense. The intake system after the maf is sealed off in an open breather system. You can close off the open breathers and nothing changes in signal, open them up while watching the logger and nothing changes. Maf signal, a/f, trims, etc all stay the same.
I've logged and watched the maf signal and tune going from fully closed to an open breather system and it affects metered air zero. The only way metered air is changed is if fresh air is introduced into the intake after the maf. If you have a closed intake system (no pvc attached to it) then nothing is going into the intake. On top of that the crankcase is always pushing air OUT from the catch can not sucking air in. So there is no way for air to actually get back into the intake from the outside.
hook up some vac lines to the catch can and do some logs. It is never pulling fresh air into the crankcase and even if it did the air from the crankcase will not magically get into the intake system unless it's somehow forced up the crankcase and past the piston rings.
I'm not sure how you think fresh air is getting back into the intake from a crankcase breather. It just doesn't make sense. The intake system after the maf is sealed off in an open breather system. You can close off the open breathers and nothing changes in signal, open them up while watching the logger and nothing changes. Maf signal, a/f, trims, etc all stay the same.
05-28-2012, 12:10 PM
#49
The reason we're running catch cans is to mitigate the 'gumming' issue.
I've logged and watched the maf signal and tune going from fully closed to an open breather system and it affects metered air zero. The only way metered air is changed is if fresh air is introduced into the intake after the maf. If you have a closed intake system (no pvc attached to it) then nothing is going into the intake. On top of that the crankcase is always pushing air OUT from the catch can not sucking air in. So there is no way for air to actually get back into the intake from the outside.
Here are the paths that air takes.
Intake > MAF > Plenum > Cylinders > Exhaust
(Also the blowby route can include from cylinders > Crank > PCV valve > Plenum)
Intake > MAF > Crank intake > Crank > PCV valve > Plenum (cycle)
Either way, all the air that is metered, goes through the engine one way or another, and that was my point, it's expecting that and is getting that.
I'm not sure how you think fresh air is getting back into the intake from a crankcase breather. It just doesn't make sense. The intake system after the maf is sealed off in an open breather system. You can close off the open breathers and nothing changes in signal, open them up while watching the logger and nothing changes. Maf signal, a/f, trims, etc all stay the same.
it's currently locked in the office until tomorrow, i'll get as much taken/posted as possible in the next two days.
05-30-2012, 05:30 AM
#54
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Here are the paths that air takes.
Intake > MAF > Plenum > Cylinders > Exhaust
(Also the blowby route can include from cylinders > Crank > PCV valve > Plenum)
Intake > MAF > Crank intake > Crank > PCV valve > Plenum (cycle)
Either way, all the air that is metered, goes through the engine one way or another, and that was my point, it's expecting that and is getting that.
Intake > MAF > Plenum > Cylinders > Exhaust
(Also the blowby route can include from cylinders > Crank > PCV valve > Plenum)
Intake > MAF > Crank intake > Crank > PCV valve > Plenum (cycle)
Either way, all the air that is metered, goes through the engine one way or another, and that was my point, it's expecting that and is getting that.
The bolded path above. Where is that path on our engines? Our drivers side port is attached before the maf and will pull crank gases out of that bank via vacuum when driving and the passenger side vents to the plenum like the first path you listed. I don't see a path from post maf directly into the crankcase on our cars.
05-30-2012, 11:51 AM
#55
I may be wrong here, but there is no tube on the intake that comes off before the MAF. The MAF is right next to the air filter at the start of the intake tract.
Secondly, the "intake tube to drivers side port" is not pulling air from the crank, it's allowing air to travel into it. The pull from the plenum to the PCV valve (passenger side) causes it to travel in that direction.
Secondly, the "intake tube to drivers side port" is not pulling air from the crank, it's allowing air to travel into it. The pull from the plenum to the PCV valve (passenger side) causes it to travel in that direction.
05-30-2012, 12:05 PM
#56
I had a catch can on my Cobalt Turbo...didn't catch much. It vented back into motor. Maybe I'm off base here, but I see NO REASON to use one in this car if it's NA. You're in Vacuum all the time..no positive intake pressure. My HR burns/ uses almost ZERO oil over 6k mile OC intervals (1/2 Qt).
05-30-2012, 03:40 PM
#58
what binder is saying is the same thing i was saying. both ports are seeing the exact same amount of vacuum so while the fsm might say thats how it works it dosnt, for the system to work like how honda and nissan say it does would require it to defy the laws of physics and fluid dynamics. i understand how nissan is saying it works and i see what you think it makes sense, vacuum at pcv causes everything to be pulled in from the other back port on the valve cover but it dosnt work that way because that port see vacuum as well. the picture in the fsm that shows it pulling from the pcv and the drivers side valve cover at the same time is the only way the system will work. the only way any air is going to go into the crankcase from the intake is if your boosted.
like i said the only way for it to work with pushing air into the crankcase with vacuum would be a high pressure area in the intake that would lead to the port on the intake for the drivers side valve cover. which would require fast moving air and putting a wall in the airflow, which the intake dosnt have. the car has 0 ways for air to be pushed into the crankcase. the fsm is wrong, and if you think that theres no way nissan can be wrong because they make the car and are a large manufacturer then go try and get a bosch oil filter for our car, large auto manufacturers make mistakes all the time. my guess is that is in referance to another vehicle that has a vacuum pump on it so it works that way or turbocharged vehicles. the fsm also makes mention about turbochargers precautions which our vehicle does not have from the factory(and the system would actually work the way they describe it if it where turbocharged.)
bottom line bro is the fsm is wrong in many many many places. just because a book says something works some way dosnt mean it can defy physics and fluid dynamics. im guessing you will find that same diagram on every single nissan vehicle.
like i said the only way for it to work with pushing air into the crankcase with vacuum would be a high pressure area in the intake that would lead to the port on the intake for the drivers side valve cover. which would require fast moving air and putting a wall in the airflow, which the intake dosnt have. the car has 0 ways for air to be pushed into the crankcase. the fsm is wrong, and if you think that theres no way nissan can be wrong because they make the car and are a large manufacturer then go try and get a bosch oil filter for our car, large auto manufacturers make mistakes all the time. my guess is that is in referance to another vehicle that has a vacuum pump on it so it works that way or turbocharged vehicles. the fsm also makes mention about turbochargers precautions which our vehicle does not have from the factory(and the system would actually work the way they describe it if it where turbocharged.)
bottom line bro is the fsm is wrong in many many many places. just because a book says something works some way dosnt mean it can defy physics and fluid dynamics. im guessing you will find that same diagram on every single nissan vehicle.
I may be wrong here, but there is no tube on the intake that comes off before the MAF. The MAF is right next to the air filter at the start of the intake tract.
Secondly, the "intake tube to drivers side port" is not pulling air from the crank, it's allowing air to travel into it. The pull from the plenum to the PCV valve (passenger side) causes it to travel in that direction.
Secondly, the "intake tube to drivers side port" is not pulling air from the crank, it's allowing air to travel into it. The pull from the plenum to the PCV valve (passenger side) causes it to travel in that direction.
05-30-2012, 06:08 PM
#59
I had a catch can on my Cobalt Turbo...didn't catch much. It vented back into motor. Maybe I'm off base here, but I see NO REASON to use one in this car if it's NA. You're in Vacuum all the time..no positive intake pressure. My HR burns/ uses almost ZERO oil over 6k mile OC intervals (1/2 Qt).
05-30-2012, 06:24 PM
#60
The drivers side just has the intake air blowing that way.
for the system to work like how honda and nissan say it does would require it to defy the laws of physics and fluid dynamics. i understand how nissan is saying it works and i see what you think it makes sense, vacuum at pcv causes everything to be pulled in from the other back port on the valve cover but it dosnt work that way because that port see vacuum as well.
I do however think, that i know what you're saying about the intake pipe, wind rushing past the end of it should technically create a vacuum at the intake tube end. However, it has to suck air from somewhere, the PCV valve is one way, so it can't travel that way.
Engine pulls from the drivers side/intake tubing. The system is sealed, the intake speed would have to create a vacuum waaay more powerful than the one the plenum is creating (on the other side) for it to be flowing back into the intake tubing.
You don't get oil on the front side of the butterfly, just the back side.
Not really sure what you mean about buying a Bosch oil filter, i use them all the time...
Yeah, i would imagine it is, they all use the same system, nearly (if not actually) all modern cars use the sealed PCV system.