Alright, so I've been on a quest to add a catch can to my system and that has lead me to quite a few discoveries and realizations. Basically, I'm starting this thread to not only show how to design a pcv system, but also to help further the understanding of our pcv system and pcv systems in general, as well as diperse several myths on our system, especially those from L36 to L26 intake swap.
As a note, I will be updating this as I go, so feel free to comment if I missed something or you have any questions.
INTRODUCTION TO PCV
Air wants to reach a state of equilibrium where the pressure is the same. Therefore, that is why your pcv system even works in the first place! Blow-by of excess combustion gasses passes by the rings and into your crankcase pressurizing the crankcase. If left, the pressure will force it's way out somewhere, and that somewhere is the various gaskets causing the pressure and oil to leak out (not good). So we need a way to relieve that pressure. At first, we simply put breather caps on each valve cover and called it a day, however, this keeps fuel/ combustion vapors, contaminants, and condensation trapped in your crankcase causing the oil to get dirty quicker. That's part of the reason for the old 3000 mile oil change that old cars needed (obviously not the only factor). To combat this, engineers put a hose going to the intake where low pressure vacuum (sort of like suction if you will) on one head to vent the crankcase gasses, and another hose to draw fresh air in before the throttle body. The pcv valve is to meter the flow of air and keep pressure from pushing past into the crankcase (boost/backfire). The fresh air cycles the unwanted combustion vapors and in-turn keeps the oil cleaner and keeps your engine from running poorly and leaking everywhere. The whole cycle works on the fact that air moves from areas of high pressure (crankcase) to low pressure (manifold). In a sense though, your pcv system is a "metered" vacuum leak. Thus why them sticking closed causes so many problems.
PROS AND CONS
Pro:
-Keeps your oil cleaner and traps all contaminants and condensation
-Keeps your intake and throttle body cleaner (ever looked at a 200,000 mile intake on these cars?)
-For turbo systems, allows correct pcv operation without boost leak (see special turbo section below)
-Potentially keeps your map sensor working longer (requires map sensor relocation)
Cons:
-It's something else to remember to empty from time to time.
-It does cost money
-It takes up some space
-like any lines or fittings, it adds places where you can potentially have a vacuum leak, so be careful
HOW IT WORKS
Let's start with a diagram showing the path for our pcv systems. I'm going to break this into two parts, L36/L26 and L67/L32 systems. You'll see pretty quick why I'm breaking them up as they do have differences
L36/26
Green arrow is Intake Air
Yellow arrow is where the air pressure is neutralized
Red arrow is crankcase pressure going to pcv valve and vented to manifold vacuum
Blue arrow is L26 intake air path (differences noted later)
L67/32
Green arrow is Intake Air
Yellow arrow is where the air pressure is neutralized
Red arrow is crankcase pressure going to pcv valve and vented to manifold vacuum
Blue arrow is L32 intake air path (differences noted later)
One thing to note at this point is that the intake and pressure are reversed from L67/L32 and L36/L26.
Second is that gen 2 pcv intake is through the throttle body, whereas the gen 3 pcv intake is external for a short point and doesn't go through the throttle body. That's where most people get confused.
Our system is different from some other more conventional pcv systems only because it is routed internally instead of through the valve covers like most systems. It's a cool design really, and it saves on hoses and leaks, but there's one problem, you can't modify it easily!
THE BUILD
L36/L26
This is the hole on the L26 that the "runner" for the pcv vacuum goes to. It needs to be plugged if you are going to modify the pcv system for a catch can. Essentially, what we are going to do is "re-route" the pcv vacuum from the pcv valve to another vacuum source (thus why you need to plug the internal one).
Red is the crankcase pressure from the valve cover, green is the vacuum hole shown above. I chose to use a combination of jb weld and tapping a really small npt pipe plug tp close off the vacuum port.
Here's the inside of the catch can I decided to go with. I'm not endorsing or posting a link at the moment because I never endorse something without thoroughly testing it first. However, I strongly suggest you get a quality catch can that has baffles and filters like this one or better. Morimoto makes some really high quality catch cans.
Here's a picture of what my engine bay looks after install (catch can is located on the back fire-wall under the strut tower brace)
Closeup of catch can (I know, It's messy)
This is where the maf sensor is located stock. I opted for a T branch which I plugged temporarily with a bolt so that I have a port to test for vacuum leaks with my smoke tester. Don't worry, once I feel good with the tests, I'm going to cap it properly. You might note that my map sensor is missing. You can tee off the old location where I have the "smoke tester port". I opted to locate mine off the evap vacuum hose by the throttle body. This way it doesn't get clogged with blow-by oil like the oem location which tends to kill the sensors over time. If you're wondering if this is ok to do, I've thoroughly tested both setups with no fuel trim changes, plus remember that the L67/L32 folks map sensor's are already run off the throttle body externally! The T is 1/4" bottom by 3/8" sides if I recall.
You have options here. I opted to tie into the old evap vacuum port on the L26 when I did the swap, but you can tie into really any vacuum source as long as it's adequate. A favorite is the plug on the throttle body by the evap/fpr vacuum source. Just tapped a 1/4" npt with 3/8" barb.
Now this is not exactly what I recommend, but it's what I'm dealing with right now. The vertical pipe form the manifold is the fresh air intake referenced in the schematic. Running the hose vertical runs into the hood and pinches the hose, so you'll need to make a right angle. I had an old spark plug wire boot lying around so I used that and a 3/8" coupler. Best scenario would be to either get correct molded rubber or remove the pipe and tap a right angle barb.
This is where the air intake comes from which leads to the pipe above. You won't have this. This is a special throttle body adapter made by one of our members here. Here's a link: Gen 5 (L32/L26) to L67/L36 Throttle Body Adapter Plate GTP GT SSEi GS Ultra | eBay he's a great guy and I highly recommend his products.
This one is a L36 to L26 throttle body adapter with pcv tapped into. Basically, you remember the blue lines in the diagram? Well, since the L26 uses external pipe to run the intake to before the throttle body but after the maf sensor, this adapter ties into the stock L36 port on the throttle body. Another way is to simply tap a port anywhere on the throttle body before the throttle blade but after the maf sensor (it's metered air).
That being said, I have simply run a filtered vent from autozone with no adverse changes in fuel trims at all, so you decide the route you want to go. Personally, I trust the K&N a lot more than I do a spectre filter, and its less maintenance. I want my oil to stay clean for a long time!
L67/32
The only differences between the L36/L26 and the L67/L32 is that the head functions are swapped (aka, the head where fresh air is delivered is opposite from the crankcase pressure head). This is why you can get away with tapping the oil cap for fresh air intake on supercharged engines if your intercooler is too big (see other pcv threads).
Therefore, on supercharged applications, in the port where the pcv valve goes on the supercharger, there is a hole in the side that vents to before the supercharger. You need to plug this since we will be routing the vacuum externally, just as above with the L36/L26.
Now, since L67/L32 has a nice metal cover for the pcv, all you have to do is drill and tap an barb fitting on top of it, preferably a right angle due to height concerns.
The rest of the routing is exactly like the L36/L26 section above. As noted above, if you have a intercooler that covers the pcv intake port, you will have to tap the front valve cover and run a hose to the intake location much as noted in the L36/L26 section.
Note: I will eventually perform this on a supercharged car and post pictures, but right now, this is what I have.
MYTHBUSTERS
1. "You need to drill through the vertical stove pipe and plug the vertical pipe when doing a L36 to L26 intake swap"
Absolutely not! If you have this done to your car currently, stop immediately and fix it! You don't have a functioning pcv system. Why? Well, if you understood the diagrams above, you'll notice that the vertical pipe is the fresh air intake for the pcv system. By drilling through the side through the vertical pipe's path and into the manifold, you are tying the fresh air intake to vacuum. If you understood the intro section on how pcv works, you'll notice a problem. If the fresh air intake is routed instead to vacuum, the path of "least resistance" will be the air intake. Basically, instead of the system feeding fresh air in the intake and expelling crankcase vapors and pressure out the pcv valve, the system will bypass the pcv valve and "exchange" pressure through the air intake now routed to vacuum. Again, see the intro section to see why that's bad (it's the same as simply running breathers).
2. "You need to run a breather on the vertical pipe"
True, you CAN run a breather, but look at the stock L32/L26 pcv air intake, and you'll figure out why running it like I did also works. (I discuss in the build some pros/cons of each)
Other myths like "you don't need a catch can EVER", "breathers work fine for me", "catch cans don't work", and the lot I won't be discussing here as they have all been discussed in length elsewhere.
TURBO/HIGH BOOST
The section you've all been waiting for! Well, I hate to disappoint, but there's really not much different in designing a boost pcv system for our vehicles as n/a.
The main difference to note is that while the pcv valve does a great job of keeping backfires from pressurizing the crankcase, they're pretty lousy at keeping boost pressure out. Good news is that the only thing you need to add to the system is a check valve on the line running to the catch can. This keeps boost from pressurizing the crankcase under high boost/racing.
It's also advised on turbo applications to add a second catch can in the fresh air intake line. If you have a L32/L26 gen 3, you've got it made. You have to route the intake external from the vertical pipe. Just tap in there. If you have a L67/L36, well, you'll have to drill and tap into the air intake port running the the throttle body and cap it off at the throttle body. You have to do this regardless of the catch can as your pcv intake needs to be before the turbo. On all systems, you'll have to tap in before the turbo, and run it through the catch can to your vertical air intake pipe.
And that's it! Now your boosted application has a safe, fully functioning pcv system that is easier to tune, and will keep your engine from leaking and oil cleaner!
CLOSING
I really hope this helps dispel some of the myths out there and help everyone better understand the functioning of our pcv system. As I've referenced to several times in the build sections, the way I did my build works, but if you understand the underlying principles outlined here, you can customize and improve upon my design as much as you want! There's really quite a few ways to do this (though, please avoid vented systems).
As always, discussion is welcome, and I hope this helps!
