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09 Altima 3.5SE 6MT Sedan
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Discussion Starter · #1 · (Edited)
So my Mishimoto catch can just arrived and I'm planning the install....

I had originally just planned to insert it between the PCV and the IM and let it do its thing..and I still will, but my question is this:

If during WOT the flow in the 'other' PCV hose reverses (this is the hose from the air cleaner to the valve cover) due to increased amounts of blow by gases then it can inject oily vapor into the intake via the intake snorkel.

The worst thing to do is block this off, this causes sludge accumulation due to condensation of combustion vapors and crap mileage because you in effect reduce the internal engine case pressure (by removing the pressurized clean air flow) which actually INCREASES the amount of blow by at any RPM.

Some people have addressed return path by simply venting this line, sometimes with a cute little mini filter..which allows air in and vents blow by to the engine compartment. As I understand it, this approach is bad for two reasons, first because the intake snorkel pressure is higher than ambient it actually 'blows' air in to the engine rather than expecting a more passive approach but worst because you are now allowing unmetered air (air that has not passed the MAF) to enter into the engine and ultimately the intake via the PCV.

So I'm largely inclined to leave that line alone, but was wondering if there was a third option out there...ie a 3-way T valve that would allow metered air to flow into the valve cover, but during WOT when the pressure reverses due to blow by, would block the path to the snorkel and instead vent those gases into the engine compartment? Did some preliminary searching but didn't find much...anyone done this? Is it even worth fussing about?
 

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Hi d0ugmac1,

Im on the same plans to reduce the oil on the intake. For venting the line and evade the unmetered air issue, IMO I would just put also a mini air filter in the inlet of the other valve cover (if your engine is the VQ35) and put a vacuum cap on the intake tube. And for the PCV valve, just put an air filter too and a vacuum cap on the intake manifold.

Any other suggestions are welcome.
 

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09 Altima 3.5SE 6MT Sedan
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Discussion Starter · #3 ·
Hi d0ugmac1,

Im on the same plans to reduce the oil on the intake. For venting the line and evade the unmetered air issue, IMO I would just put also a mini air filter in the inlet of the other valve cover (if your engine is the VQ35) and put a vacuum cap on the intake tube. And for the PCV valve, just put an air filter too and a vacuum cap on the intake manifold.

Any other suggestions are welcome.
I'm pretty sure you don't want to cap off the system as it's actually beneficial most of the time (especially when the throttle plate is all but closed at idle as the PCV system provides a neutral way to sneak metered gases to intake side of the TB without the manifold vacuum going through the roof). Your suggestion would lead to poorer fuel economy, higher sludge buildup and a rougher idle. for reasons mentioned in my first post
 

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09 Altima 3.5SE 6MT Sedan
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Discussion Starter · #4 ·
This question just sent anonymously:

Gentle Reader: So the best way is to put the PCV >> catch can >> intake manifold ?

d0ugmac1: Yes as that is the most common path for gases to flow (ie during idle and mild acceleration). Make sure your catch can has baffles and can handle the heat of the exhaust gases...plan on at least 200'F and higher if you live in the south with higher underhood ambients. The Mishimoto I chose (Amazon $80'ish has baffles and also a sintered bronze filter (like metal pumic stone) which helps to condense oily vapour into oil so it can drip into the catch can before exiting the CC into the intake)

If you hammer the pedal (open up the throttle valve) there isn't much crankcase flow of any kind due to manifold vacuum dropping to near zero (so pcv closes)....but once your RPMs start to build, you start to increase your blow-by amount...and at the extreme end of wide open throttle and high RPMs, you actually pressurize the crankcase with blow by and those gases are released (escape) both through the PCV and backwards through the other side (breather pipe) back into the intake snorkel again (post MAF!)....and more gas goes that way because there is no restricting PCV valve in the way.

So for 99% of your driving...PCV is good and beneficial and even better with a quality catch can in the path. However, for those leadfoots among us...I was hoping for a little 'waste valve' for that 1% of the time the VQ gets opened up!
 

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Start The Show - Jet
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Doug, I unfortunately have nothing to add at this time, but I'm in a similar boat - catch can ready to install, but figuring out how I want to do it. I literally had the same sentiment. Perhaps the Z and G peeps have some ideas from their forums... I'll research and round back once I have more info. Please post up what you find, too. :grin
 

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09 Altima 3.5SE 6MT Sedan
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Discussion Starter · #7 ·
The one suggestion I did find was a second catch can with ports reversed on the breather line side...but with the Canuck peso at it's current rate...that ain't gonna happen :) Keep thinking the waste valve has gotta exist out there....I'll keep looking. Thanks for the otterpop link BTW.
 

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09 Altima 3.5SE 6MT Sedan
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Discussion Starter · #8 ·
Interesting...maybe a little hardcore for most....apparently using exhaust venturis to draw the crank fumes. I guess it gives your cat a little extra hydrocarbon to chew on...
 

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Start The Show - Jet
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Interesting...maybe a little hardcore for most....apparently using exhaust venturis to draw the crank fumes. I guess it gives your cat a little extra hydrocarbon to chew on...
Would it need to be pre-cat so it gets burnt up, or could you just pull the fumes into the exhaust post-cat and call it good?
 

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09 Altima 3.5SE 6MT Sedan
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Discussion Starter · #10 ·
Would it need to be pre-cat so it gets burnt up, or could you just pull the fumes into the exhaust post-cat and call it good?
IMHO, for the venturi to work you would need near linear flow...so it would have to be inserted in a relatively straight length of pipe away from perturbations...which doesn't exist in our VQ setups until about where the primary cat is at the earliest (assuming you don't have the RL Y pipe). Insertion after the last cat element would mean your emissions would be likely out of spec on a tailpipe test. Idea might work better on the QR setup....not as familiar with the exhaust routing on that.
 

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Start The Show - Jet
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IMHO, for the venturi to work you would need near linear flow...so it would have to be inserted in a relatively straight length of pipe away from perturbations...which doesn't exist in our VQ setups until about where the primary cat is at the earliest (assuming you don't have the RL Y pipe). Insertion after the last cat element would mean your emissions would be likely out of spec on a tailpipe test. Idea might work better on the QR setup....not as familiar with the exhaust routing on that.
I love Michigan... no emissions testing, so no issues. Others are not so lucky, though.
 

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I know this post is almost three years old, but in the end what did you do with this?
I have just cleaned the intake manifold and want to install a catch can once I receive it, my idea was to put it only between the PCV and IM but after reading this I'd like to know from your experience what worked better for you
 

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09 Altima 3.5SE 6MT Sedan
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Discussion Starter · #13 ·
I know this post is almost three years old, but in the end what did you do with this?
I have just cleaned the intake manifold and want to install a catch can once I receive it, my idea was to put it only between the PCV and IM but after reading this I'd like to know from your experience what worked better for you
I wound up taking the Do-Nothing path...so my Mishimoto can is still in its shiny plastic. As far as I can tell, Nissan already had integrated something along the lines of what I was trying to do...the Gen4 VQs have this funny plastic box/cube on the hose between the valve cover and the intake snorkel. My guess is that it already does what I wanted to do...ie siphon crankcase fumes during normal operation and vent positive pressure during WOT events.
 

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All it should do is trap more solid matter like a valve cover baffle does. The PCV commonly plugs into a baffle source too.

If the engine has an EGR valve a lot of the intake deposit is from that mixed with backflow fuel from the injection. You think it's oil but commonly not, more like reduced VOC fuel remains plus EGR carbon. Once engine gets older then blowby makes it a higher % of oil.

I used to run AMC street race engines sealed with no PCV and a combined intake and exhaust vacuum extraction system, the cars went everywhere with crankcases at 10-15 Hg. of vacuum on them 100% of the time.
 

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My 2010 3.5L VQ was throwing a smoke screen that obscured the neighbors house only on start up. Cleared by the time I left the driveway. I bravely tore into the engine and replaced the valve seals. Proud of myself, and finishing up. Pulled the IM from the tote and found it was sitting in a puddle of oil. More would drip out as I handled it. Now I'm depressed thinking that this was the problem all along... not the valve seals on the other side of cam shafts and timkng chains. Ugh. So the 'do nothing' approach is not an option for me. Is my answer to replace the PCV valve and buy the Mishimoto catch can?
 
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