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2001 Impreza type R
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192 Posts
Discussion Starter · #1 · (Edited)
Today I connected my PCV Hose from the block and 2 Crankcase breather hoses, all to a oil catch can, then connected the output side to my pcv valve on the intake manifold. Therefore all the oil blowby in all three of these hoses is being filtered out before the air is sucked back into my intake manifold. Also plugged the two tubes on my cobb intake for vacuum lines, since the hoses now go to the catch can instead..

What are your guys's thoughts and ideas on this?


Quick sketch of it. lol
 

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Meany Head
2000 RSC
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10,236 Posts
With a MAP based car, you don't have to worry about metered air. So, your setup is ok there. If you had a MAF car, you'd have a problem for sure.

That said, you've unfortunately removed the air-circulation ability of your PCV system by T-ing in all the lines to a single point. You've also removed the ability for WOT blow-by gases to escape anywhere. Remember, the PCV works only on vacuum. Any pressure behind it will shut the PCV closed. So, WOT is going to build up pressure and possibly start to blow your your seals.

There are 2 things needed for a typical PCV setup, fresh air circulation, and somewhere for blow-by gases to escape.

The ideal way the hoses should be configured is such that fresh/filtered air can be sucked into the valve covers, then dirty crank-case air is drawn from the crank-case port into your PCV. So, your catch-can should ideally be placed between the block and the PCV valve.

On my car, I have both valve cover ports T-d together with to a single small air filter. I could have (and still might) used 2 small air filters, one for each port. Then, my block port goes right to my PCV valve. I have yet to install a catch-can though. At WOT and under boost, any built up crank-case pressure is vented to the Atmo via the Valve Covers. If I wanted to also catch this gunk, a 2nd catch-can would be needed.

On a MAF car, the air drawn in through the valve covers MUST be pulled in from the intake track, somewhere after the MAF sensor.
 

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Meany Head
2000 RSC
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10,236 Posts
:)

Under normal driving and typical vacuum situations, the valve covers do indeed take in air. Under WOT when more blow-by builds in the crank case, dirty-air can be forced out the valve cover ports as well as the block port. Hence why they are all routed to the big black intake box in stock configuration.
 

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2001 Impreza type R
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192 Posts
Discussion Starter · #10 ·
I have changed my setup and now have the two crankcase breathers attached to my intake pipe, and my pcv hose goes to catch can then to pcv valve.

This works correct?
 

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98 Impreza RS/04 FXT
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191 Posts
Alright,
I'm bumping this thread over a few others mostly due to Skidd's excellent explanation. Quick reason why: right now I'm driving an 04 Forester XT. Closing in on 200k miles it already killed one turbo, so anything that filters contaminants is a plus in my book. I don't want to purchase an expensive system, and I prefer to do my own work. I also want a few things confirmed/cleared up.

I understand the use for two catch cans, and plan to use both. For the first one, it goes between the rocker vents and air intake. My understanding is that the vents pull in air unless under heavy acceleration, where oil/crud gets forced out. So, the catch can should be oriented with the flow from the vents to the air intake correct?

The second one seems to be the confusing one. My understanding of the system it involves is: the crankcase vents to the intake manifold (abbrev. as IM) via the PCV valve. A line runs from the air intake to the PCV valve as well. Air always runs from the crankcase to the IM. Normally, the air intake line feeds additional air in to the IM via the PCV. Under hard driving conditions this line becomes a vent line.
I have seen the catch can placed between the PCV and IM (from a DIY on this site) as well as between the PCV and line to the air intake. It seems to me the proper place to place the catch can is between the crankcase and PCV, which I think is what Skidd is saying in this quote:
The ideal way the hoses should be configured is such that fresh/filtered air can be sucked into the valve covers, then dirty crank-case air is drawn from the crank-case port into your PCV. So, your catch-can should ideally be placed between the block and the PCV valve.
Furthermore, the catch can would be oriented for flow from the crankcase to the PCV.

Sooooooo...
Am I correct with my reasoning?
Also - with the first catch can, is it reasonable to assume most catch cans/compressor filters will allow for appropriate air flow both ways?
 

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Meany Head
2000 RSC
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10,236 Posts
Your thought on the Catch-Can used for the valve-covers sounds right to me. It's used to catch oil being forced out the valve covers under WOT and heavy boost.

To clarify, I might have mis-spoke on one regard... I think the catch-can should ideally be between the PCV and the IM. I can't think of why I might have suggested it go between the block and PCV. Unless I just wasn't paying attention to my acronyms.

In other words, I think you have it all correct Fire14.
 

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98 Impreza RS/04 FXT
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191 Posts
Well I took care of the catch can for the valve covers on the cheap. A friend of mine had a catch can intended for a brake bleeding kit, which I got for free. Got some small hose clamps, about 4' of 1/4" fuel hose, and decided to use a coarse 3M paint stripping pad for filter media. I figure if the pad is good enough for use with mineral spirits it should do fine with motor oil. Total cost there was about $11.

This is for a 2004 FXT


Used two zip ties to keep the hoses in order, and found the can fit down near the ABS module behind the passenger headlight. Since the can sits lower than the rest of the line, it should facilitate proper collecting. Temperature should not be an issue with this location either. Since the can is not mounted to anything (but snug) I placed a small rubber hose over the brake line that is adjacent, so nothing should wear through. I have enough slack in the hoses to pull the can out easily. The 1/4" line I sleeved into the original vent line, and used hose clamps to keep them from pulling out. Since it is not a vacuum line I didn't see the point of sourcing hard fittings there. Install was really easy - it took maybe 15 min (mostly spent determining where to run the lines), and I only used a knife and screwdriver.

Detail shot of the can location, showing proximity to brake line:


Thanks to Skidd for the advice and confirmation!
EDIT - This may have been so easy since the silencer/snorkus thingy is no longer present on the air intake. I can't remember how much real estate it took near the ABS module
 

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2006 2.5i San Remo Red SC
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My question is with hose from each valve cover to a T aswell as crankcase breather valve to catch can. The PCV valve is directly above the line of the PCV valve which gets sucked in my manifold vacuum. Whats wrong with routing that same line from PCV valve instead of to manifold vacuum rail directly to the catch can. I still notice oil being pulled from PCV into manifold via the pcv. but crsnkcase breather is on same line but goes to catch can.
Meaning half goes to catch can half goes to manifold. Shouldnt PCV go to catch can??? Pics in a minute. 2006 2.5i supercharged.
Wouldnt pluging vacuum ports with vacuum nopples and clamping them be the right way??
 

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2006 2.5i San Remo Red SC
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1,214 Posts
Here are some pics of what I mean by PCV and crankcase breather hose on same line. Don't remember how it was think it went to air box.

https://www.facebook.com/media/set/?set=a.589193401093130.1073741825.100000074267501&type=1

I use to be able to post pics but seems google chrome changed so much but you can see how I have valve covers routed to catch can aswell as crankcase breather.
The hose that I'm holding goes to the PCV which you can see with out the hose attached. Which goes to a vacuum rail seems only on 2.5i RS's did this a different route.
You can also see the two vacuum locations one on passenger runner the other on driver side runner in the back. I took these off to inspect well I took the whole vacuum rail off and noticed oil in the ports. These ports go straight to intake manifold. Sure not as bad for intercooler and supercharger but what I have noticed is your getting crankcase gases/oil mixed with air and fuel. Under boost I'm assuming the same thing. What would be the problem of removing the unused screw cap from catch can and routing a hose from PCV to catch can. Since what it seems like is just half crankcase gases going to catch can while half if not all under vacuum going to manifold.

Again sorry for the link instead of pics here. I tried to post them here but my browser is being a TOOL. what I have noticed when I tried this that I get slight oil in the catch can now from a 45 minute drive. Say 4 drops compared to nothing with catch can routed normally. Under boost the PCV valve should close which would cause gases to either go thru crankcase section to catch can or do nothing but build pressure in your crankcase.
Anyone agree or should this set up remain as pictured???
 

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2006 2.5i San Remo Red SC
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My set up is crankcase breather line to catch can,PCV line to catch can (all have their own hose) and both valve cover ports to catch can.

My crankcase breather has no check valve only PCV. before I had PCV still going into intake and saw no oil in catch can only oil residue probably from crankcase breather and valve covers.

Once I capped of my intake manifold with duel vacuum port nipples and clamped them and routed my PCV to catch can, after a weekend of driving I checked catch can and oil has started to settle which would have been in my intake manifold. Which proves to me that PCV does not need a vacuum to release its self.
I also did a compression and leak down test all passed and compression is 175 on all but #3 cylinder(178) so rarely are my rings passing on 9 psi of supercharged boost, stock motor.
I have a K&N small filter on top of Catch Can on a extra nipple due to the fact our valve covers can suck in air at times this air will still be filtered or with in the system.
5,000 miles later and catch can draining system works just fine.
Don't know about the turbo set up but for FI SC on a N/A I have no issues and car still runs great with 34k on motor.
 
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