UA-65274002-1 Jump to content
wstefan20

The PCV Thread

Recommended Posts

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)

 

 

L36_PCV_diagram.jpg

 

 

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)

 

 

L67_pcv_diagram.jpg

 

 

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).

 

 

20171130_100803.jpg

 

 

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.

 

 

20171129_130815_747x1328.jpg

 

 

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.

 

 

20180207_201028.jpg

 

 

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)

 

 

20180207_212036.jpg

 

 

Closeup of catch can (I know, It's messy)

 

 

20180207_212049.jpg

 

 

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.

 

 

20180207_212105.jpg

 

 

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.

 

 

20180207_212119.jpg

 

 

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.

 

 

20180207_212128.jpg

 

 

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: https://www.ebay.com/itm/Gen-5-L32-L26-to-L67-L36-Throttle-Body-Adapter-Plate-GTP-GT-SSEi-GS-Ultra/112433749258?hash=item1a2d92dd0a:g:ZIoAAOSwSlBYzYzg:sc:USPSFirstClass!64133!US!-1&vxp=mtr 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! 

 

 

20180207_212143.jpg

 

 

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! :)

Share this post


Link to post
Share on other sites

Looks nice. I've wanted to make a catch-can for my TGPs. You mention intake manifolds at 200k miles. Even today, I've found many, if not most vehicles, removing the intake manifold results in dumping a not insignificant amount of oil on the ground when they are tipped. From my experience, it's worse now on todays engines that it was a couple decades ago, and engines also seem to use more oil now than they did back then. I see a lot of customers get upset over how much oil their brand new vehicle uses. I'm surprised engineers don't build some internal baffling in valve covers to keep that crap out of the engine. It doesn't seem like it'd be that difficult.

Share this post


Link to post
Share on other sites

P.S. If anyone knows how to fix the formatting from squishing everything together and removing my spaces, I'd really appreciate it!

Collateral damage of mobile devices. Using a PC to edit and re-format it will make it right.

Share this post


Link to post
Share on other sites

Looks nice. I've wanted to make a catch-can for my TGPs. You mention intake manifolds at 200k miles. Even today, I've found many, if not most vehicles, removing the intake manifold results in dumping a not insignificant amount of oil on the ground when they are tipped. From my experience, it's worse now on todays engines that it was a couple decades ago, and engines also seem to use more oil now than they did back then. I see a lot of customers get upset over how much oil their brand new vehicle uses. I'm surprised engineers don't build some internal baffling in valve covers to keep that crap out of the engine. It doesn't seem like it'd be that difficult.

 

You actually are on to something there jman. I might end up revising my design and just move everything external since it does seem to suck up quite a bit of oil. I think this can be a fun experiment though since most owners just attribute this oil loss to worn piston rings or valve guides. My engine has brand new EVERYTHING so if my catch can catches a lot of oil, I can basically prove that it is the pcv to blame. 

 

Found quite a few builds that reference designs for better baffle protection in the valve covers. Ours literally sucks straight from the heads! I'm betting that with turbo and high boost applications that this is even more exaggerated. 

 

Fortunately though, on the n/a L36/L26, the heads are reversed from the supercharged. Meaning that the crankcase pressure is vented through the front head, so all I'd have to do is remove the front valve cover, add baffling under the oil cap, and tap the oil filter cap for a barb and run the pcv inline, so not a big deal.

 

On the flip side, if you have supercharged L67/L32, your heads are reversed, meaning you'd either have to tap both heads and re-run pcv, or you'd have to tap the rear head, install baffling, and run pcv inline. A little more work than n/a.

 

Regardless, I plan on eventually installing the baffling and running the pcv external to compare the rate of blow-by. 

Share this post


Link to post
Share on other sites

Well, less than 200 miles later. Here's what I caught (after spilling more than half of it):

 

20180224_113442.jpg

 

Mind you, this is on a n/a L36 newly rebuilt engine with brand new pistons and rings. I can't believe all that was going into my intake....

Share this post


Link to post
Share on other sites

Ring gap.

 

New motor.

 

I bet by the time everything settles by this time next year it'll be much less than that.

 

Most of the buildup in the intakes that are described are usually from carbon build-up from the EGR.

 

On all my top end cleaned cars I ever worked on that I deleted the EGR from, there was never any signs of build-up or staining from an oil or exhaust based substance.

 

Just quality GM designs that don't really need improving because they aren't going to make that much of a difference; however kudos to trying to improve it, but I'd rather put my time elsewhere.

Share this post


Link to post
Share on other sites

Ring gap.

 

New motor.

 

I bet by the time everything settles by this time next year it'll be much less than that.

 

Most of the buildup in the intakes that are described are usually from carbon build-up from the EGR.

 

On all my top end cleaned cars I ever worked on that I deleted the EGR from, there was never any signs of build-up or staining from an oil or exhaust based substance.

 

Just quality GM designs that don't really need improving because they aren't going to make that much of a difference; however kudos to trying to improve it, but I'd rather put my time elsewhere.

Lol wish I could agree with you blue, but I have performed a leak down test and compression test on all cylinders and have 160psi in each cylinder with all of them within 2psi of each other, and I'm showing good for leak down.

 

The engines that I've tore apart are coated with oil sludge not EGR carbon. I'm not saying that EGR doesn't play a part, but it doesn't account for oil.

 

But you are correct, it probably doesn't matter unless your running a ton of boost. I just like a clean intake.

 

Edit: I definitely agree that's it's possible it'll decrease since the engine only has 6000 miles since rebuilding. And yes, I'm very glad I listened to you on the egr though.

Share this post


Link to post
Share on other sites

The L36 PCV was innovative. The only gripe I have with it is that the MAP sensor clips are so fragile.

There's nothing out of the ordinary about a little oil coming out, old engines would get a little film of oil in the air cleaner.

Share this post


Link to post
Share on other sites

The L36 PCV was innovative. The only gripe I have with it is that the MAP sensor clips are so fragile.

There's nothing out of the ordinary about a little oil coming out, old engines would get a little film of oil in the air cleaner.

Agreed, it was a good idea because internally, you have less hoses and thus less likelihood of leaks, and it's cheaper to produce. I think the issue is that there is really no baffling present so it tends to suck up some oil. Granted, the amount over a standard oil change is probably undetectable, but it's enough to coat your intake over 200,000 miles! And yes, the map clips are garbage.

Share this post


Link to post
Share on other sites

If the system is so great why does it fill the intake manifold with oil?

 

The factory map sensor clip was garbage but GM upgraded the part in kit # 89017274.

 I have had no trouble removing the map sensor with the upgraded clip.

post-372-0-91536700-1519885253_thumb.jpg

Share this post


Link to post
Share on other sites

If the system is so great why does it fill the intake manifold with oil?

 

The factory map sensor clip was garbage but GM upgraded the part in kit # 89017274.

I have had no trouble removing the map sensor with the upgraded clip.

Lol I should have been more specific. What I meant was that the pcv system as a design being internal is a very innovative design, not that it was implemented correctly... and yes, the clip helps, my main beef is with the map sensor itself, as it commonly just separates into two halves when trying to remove it. It's just cheaply made. Though, it was 15 years old and I've had it off a few times, so I really can't complain about the map too much. It's placement was what was really dumb though. I mean, right overtop the pcv that squirts oil on it?? Lol

Share this post


Link to post
Share on other sites

Lol wish I could agree with you blue, but I have performed a leak down test and compression test on all cylinders and have 160psi in each cylinder with all of them within 2psi of each other, and I'm showing good for leak down.

 

The engines that I've tore apart are coated with oil sludge not EGR carbon. I'm not saying that EGR doesn't play a part, but it doesn't account for oil.

 

But you are correct, it probably doesn't matter unless your running a ton of boost. I just like a clean intake.

 

Edit: I definitely agree that's it's possible it'll decrease since the engine only has 6000 miles since rebuilding. And yes, I'm very glad I listened to you on the egr though.

 

I wish I could agree with your post, but you didn't pay for the pizza so I'm chalkin' up an L for you, pookie.

 

:)

Share this post


Link to post
Share on other sites

I wish I could agree with your post, but you didn't pay for the pizza so I'm chalkin' up an L for you, pookie.

 

:)

Oh my gosh I completely forgot about that!  :eek:  

 

Well, I guess that means that you just have to come by and help me fix stuff so I can buy pizza and beer!  :mrgreen:

Share this post


Link to post
Share on other sites

Well, I'm fairly new to vacuum gauges, but looks like all is well. I'm at a little above 1000ft elevation so I'm not concerned about the reading being around 17psi. Idk, you guys be the judge:

 

[VIDEO]

[/VIDEO]

Share this post


Link to post
Share on other sites

Dude, I know you're in Fiero mode right now but I saw something on my L31 intake once it got in the light and immediately thought of you. The L36 O-ring is a little thinner but fits right on the L31 doodle. Mine is a 2001 L31 5.7L.

Including a picture of it in it's native environment and on an L36...

 

post-3252-0-45843800-1521411792_thumb.jpg

 

post-3252-0-28961800-1521411814_thumb.jpg

 

post-3252-0-58872400-1521411833_thumb.jpg

 

post-3252-0-88671200-1521411852_thumb.jpg

 

post-3252-0-19302600-1521411866_thumb.jpg

Share this post


Link to post
Share on other sites

Now here's where this could get interesting. This just went from a goofy specific little part on the L36 to a form factor. Nothing says there aren't other applications / engines with other variants of that quarter turn flange.

 

Perhaps another part is just waiting for someone to see on another engine that's got vacuum ports that are a better yet option.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×