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Discussion Starter #1
There have been many discussions about proper catch can installations lately. Most installation instructions that come with catch cans only show you how to filter the valvetrain vent lines and not the more-important crankcase vent lines. The closest-to-complete installation documented to date is the one on ScoobyMods that shows both the crankcase and valvetrain vents feeding the catch can, but good instruction for adding the crankcase vent is not included.

So here we go.....starting with the installation that we are all familiar with, the 2 lines running across the top of the engine to the catch can....



We are going to route the positive crankcase vent (PCV) line to the catch can along with our valvetrain vent line that we've already done. Instead of running another hose over to the catch can, we're going to "T" into the valvetrain vent line that is already running to the catch can, such as mine shown here:



I used a 3/8" 3-way T. We will be joining a short piece of silicone hose to this T here shortly. I had matching hose left over from my catch can installation. If you need more hose, you can order some from hosetechniques.com.



This is the PCV hose coming up from the engine block (The smaller one, closer to the turbo). If you look down near the block, you will see that the crankcase vent hose from the driver's side of the block runs over and Ts into out vent line, so we will in fact be filtering both sides of the block with this mod. The PCV hose we see here ties into the intake with a plug-style harness that is monitored by the ECU to make sure you haven't disconnected it (emissions reasons). The engine wiring diagram confirms this is nothing more than a ground signal that is sent by the ECU to the harness and the ECU watches to see that the ground signal comes back to it. You could simply short across the two wires and go from there, but I chose to keep the harness intact and just disconnect the hose from it.

So.....explanation aside, unplug the PCV harness as shown:



Use a pair of pliers or a flathead screwdriver to pry off the hose clamp near the harness. It should pop right off. The hose can then be pulled off of the grey harness with a gentle tug. I then sealed the nipple end of the harness really well with electrical tape so that nothing would enter the intake track.



You are now left with the PCV hose hanging there with an open end. Depending on how you'd like to route your hoses, you can either use the full length of hose or cut it down a little. I cut the hose approximately halfway down so that it pointed in a vertical position, not hooking to the left.

From here, I used a 1/2"x1/2" hose connecting adapter to join the end of our silicone catch can line to my newly-cut PCV hose. The 1/2" was very tight on the silicone hose side but a little loose for the PCV hose. If you could find a 1/2"x5/8" adapter (I couldn't find one), that might be a little tighter. Even with the less-than-snug fit, a seal of gasket maker around the adapter-to-PCV-hose connection and a final wrap of electrical tape finished things off nicely.



Now cut your silicone hose to a proper length and connect it to your T. You should now be looking like this.



Because the air from both the valvetrain vent and crankcase vent ultimately end up the same place, you are not messing with your MAFS by routing them this way. We are simply giving the air a different, cleaner route to take on it's way back to the engine.

As I said before, I had about 2' of hose left from the Perrin CC installation but should you need more silicone hose, hosetechniques.com is one place. I purchased the connectors from Home Depot (look for the these in the ice maker plumbing area). I'm sure the adapters can be found many places.

Now you can feel good knowing your catch can is really getting all of the nasties out of the air that your turbo, intercooler and engine are breathing in! Be sure to have some wadding or foam in your catch can so that the oil mist is pulled out of the air.

Make sense? Questions? Need more details? Let me know and we'll get this installation cleaned up for everyone's use.

Rob
 

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Nice!
How did your tank go in? I haven't actually installed my catch can yet, but I was trying to fit the can behind the light, and it looks to be a PITA. There is one wire down there that looks like it is in the way. Is it? Also, any idea why the Perrin instructions specifically say to not hook the can up to the PCV line?
 

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North Carolina Regional Forum Location ?

i have mine setup the same way only diffrence being its a greddy catch can. im thinking about changing it though as the sti service manual states the pcv and the rocker vent covers are meant for 2 totaly diffrent things. im still researching it to see if it really makes a diffrence.
 

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Any reason you didn't put the catch can near the firewall on the turbo side so you wouldn't have to run vent lines clear across the top of the engine? :)
 

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Discussion Starter #5
Perrin can was designed to fit right behind the driver's side headlight.....the hole is already there for the mounting. I didn't have a whole lot of trouble putting the catch can in. I remember others saying it was tough but I don't recall it being anything overly difficult.

Don't recall there being a wire in the way behind the headlight. It's certainly a tight fit, but nothing should need to be relocated. Not sure why they would say not to hook up to the PCV line...that's where the real problems lie. Cylinder blow-by would be a more prominent problem than whatever pressure is built up in the valvetrain. The only reason I can think that they say to not hook up to that line is because of the ECU monitoring. If you just unplug that harness, the ECU will go nuts on ya. Reroute the airflow while telling the ECU everything is cool...shouldn't be a problem here.
 

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Discussion Starter #6
ej25lvr said:
i have mine setup the same way only diffrence being its a greddy catch can. im thinking about changing it though as the sti service manual states the pcv and the rocker vent covers are meant for 2 totaly diffrent things. im still researching it to see if it really makes a diffrence.
Where did you see this reference? I'd like to look it up myself.

They are for different purposes, but both need to be filtered for the same reasons. Unless there is some concern that there may be backflow problems with a setup like this, I can't see what the issue would be.
 

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thank you Rob!! That is much appreciated!!! Now that finally makes sense, I always saw pictures of a hose going into a black abyss and I didnt want to guess and pick hoses and what not, but that is great! Helps a ton! Thanks!

Robert~
 

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Discussion Starter #10
Well, I'm guessing from your title you are referring to page EC-6. It says......

"In a part-throttle condition, the blow-by gas in the crankcase flows into the intake manifold through the connecting hose of crankcase and PCV valve by the strong vacuum created in the intake manifold. Under this condition, fresh air is introduced into the crankcase through the connecting hose of the rocker cover."

From the way they worded this, you'd almost think that they are wanting to have fresh air circulating through the crankcase. As far as I can tell, this is really them claiming a system is doing more than it really is. "Your crankcase is always fed fresh air!" Do the con rods care??

The other thing about this that baffles me is the diagram on page EC-7. Not only does it not show the vent hose coming from the other side of the block (which is clearly seen by looking at the car) but it also shows that the hose from the PCV doesn't feed into the intake tube as we see it does, but that it does so after the throttle body! If this was the case, we wouldn't have to worry about gumming up the turbo, IC and TB, would we??

I can't see where these is a concern here, but I'd love to hear opinions from any of the tuners who say that we shouldn't do this. The valvetrain vent that they tell us to filter is a free flowing system (no one-way valves that I can see, maybe we need to add one now?). As long as a there is a one-way flowing system in place to allow the crankcase to vent blow-by gases, I don't see the problem.
 

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i remember SOA or Perrin or someone saying (that when we do this mod) that we should either leave it open or leave it in circulation with the catch can and that we should NOT cap it off or something (as the perrin inlet hose does not have a spot for that piece). So Im sure its fine, it looks like its good anyways. Thanks again Rob, I sent you a PM please respond when you get a chance :) thanks.

Robert~
 

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Godspeed Stage 1+ [LONG]

yep thats the one. only diffrence i have seen on my wrx when i had it only hooked up to the rocker vents that end up running in front of the intercooler, i could see the hoses turn a shade of brown and the hose going back to the intake was clean and clear. with the way we both have it set up now i only see the hose from the pcv changing color and since it vents up it looks like whatever oil does get out simply drains back down. its brown up to the t but after that the hose going to and from the can are both clean. dunno if it makes much of a diffrence but just thought id mention it since having seen it hooked up 2 diff ways yielded kinda diff results. but im still leaving mine as is unless i can find that its really bad to have it hooked up this way.
 

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Discussion Starter #13
Oh, ok, if the question was whether to just cap off the PCV hose or not...yes, that is bad. But the capping we are doing is on the intake side, not the PCV side. We are allowing the venting to head towards the catch can.....I get the warning now. Not a concern at all.

ej25lvr, I see what you're saying as well. If the oil (in condensed, liquid form) wants to drip back down into the crankcase, that's fine by us! That's where it belongs anyway. The catch can having the long lines across the engine actually helps our case. The more surface that we give that oil to condense on, the cleaner our air will be. I can see having to disconnect the lines once a year and blowing them out or replacing them all together, but that just makes this modification all the more effective.
 

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agreed if i hear of any more pros or cons ill be sure to post them. ohh by the way if you go to my webpage you can kinds see what i was talking about :D
 

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Great write up Rob. This would be good to have in a FAQ section, I think at least a sticky for now. I plan on doing this mod myself come spring.
 

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Thank you so much, with out your help, I would probably have difficulty installing the basic catch can install yesterday, but now, since it was so easy, I'm going to Home Depot right now! Thanks Rob!
 

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I have this type of setup with the Perrin turbo intake. The Perrin excludes the PCV intake.

I did not put foam in the catch can. I put a Purolator fuel filter{part F21124} in the return line to see if there was vapor return and there has been zero vapor return in the last 90 days.

 
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