The PCV Thread

[wstefan20]

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!

[natelapolla]

This write up is awesome! Thank you. I love reading these technical posts so thank you for taking the time and detail to do this. Owner of an 05 GTP who is learning as I go.

[wstefan20]

This write up is awesome! Thank you. I love reading these technical posts so thank you for taking the time and detail to do this. Owner of an 05 GTP who is learning as I go.

Thanks! I'm glad it helps someone out! Sometimes I wonder if my "how-to's" ever get read. Lol Thanks for the feedback and good luck on your build! And remember, I'm still learning too! Don't be afraid to try stuff

[BillBoost37]

You do realize that the rings used on 3800's do not wear much and therefore these motors don't suffer from a lot of blow by as some other motors do? While this is a good mod on many motors, the 3800 is not the best candiate to do this on.

Where did you relocate the map to?

[wstefan20]

You do realize that the rings used on 3800's do not wear much and therefore these motors don't suffer from a lot of blow by as some other motors do? While this is a good mod on many motors, the 3800 is not the best candiate to do this on.

Where did you relocate the map to?

Thanks bill, I know the rings don't wear much, what I was referencing is that the pcv itself tends to suck up oil. I'm not talking about a bunch, but enough to coat the inside of your intake over 200,000 miles (I'm sure you've seen your fair share). Not saying that this is by any means a necessary mod (unless you go really high on boost), but it might keep your engine and oil cleaner in the long haul.

I t-d off of the evap vacuum source (eventually I'll be relocating it to the rear of the engine). Now it won't get oil spewn all over it like where it was originally positioned though. And yes, I did a graphical analysis of the readings both in the original location and on the evap vacuum, and they are identical.

[BillBoost37]

That may have come off as a bit harsh, sorry ... didn't realize it sounded that way. I had merely meant there are much worse out there for blow by. We drew the lucky card.

Nice on that check. Interesting tidbit, the map reads manifold pressure and by doing so it is a possible culprit when you get EGR codes like P0406 insufficient flow. Technically it's the MAP not seeing a change when the EGR is commanded open. We've seen a few folks who didn't fully understand the workings and ended up replacing a $150 egr more than once w/o any change.

Who doesn't like having trouble finding the hidden bolts because they are under 1-2 inches of oil? hahaha

[wstefan20]

That may have come off as a bit harsh, sorry ... didn't realize it sounded that way. I had merely meant there are much worse out there for blow by. We drew the lucky card.

Nice on that check. Interesting tidbit, the map reads manifold pressure and by doing so it is a possible culprit when you get EGR codes like P0406 insufficient flow. Technically it's the MAP not seeing a change when the EGR is commanded open. We've seen a few folks who didn't fully understand the workings and ended up replacing a $150 egr more than once w/o any change.

Who doesn't like having trouble finding the hidden bolts because they are under 1-2 inches of oil? hahaha

Lol naw you're fine bill! You're right though, we definitely could have dod ls4 blow by!

Good point on the egr though. Hadn't heard of that one before. I deleted my egr, but I drove for a couple hundred miles with the map relocated with no codes, maybe i got lucky? But I'll add a note just in case anyone has that issue!

Lol yeah. I was blown away when I had to re-do my lower intake gaskets (long stupid story) the intake was already coated and the puddle you mentioned was already there after only 4000 miles!!! That's when I decided enough was enough! Lol

[BillBoost37]

If you had a supercharger, you wouldn't see the issue. In case you were thinking about it.

[wstefan20]

If you had a supercharger, you wouldn't see the issue. In case you were thinking about it.

Just because you can't see it doesn't mean it isn't there! It's all the vacuum!!!



Lol but no really, I'm really thinking about top swapping.

[wstefan20]

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





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....

[cheatah faheatah]

Hard to tell, but how much is that? Like a teaspoon ?

[wstefan20]

Hard to tell, but how much is that? Like a teaspoon ?

About a tablespoon and i spilled about that much removing the plug. And this is only 200 miles.

[cheatah faheatah]

About a tablespoon and i spilled about that much removing the plug. And this is only 200 miles.

So that's where a quart or more goes between oil changes on higher mileage engines. No wonder my throttle body looked like burnt maple syrup before I cleaned it last year, prolly for the first time on this car @ 120K.

[wstefan20]

Lol yup! Yummy stuff... I hypothesized that this was happening after taking quite a few intakes off at the junkyard, but couldn't prove it till now. My guess at this point is the lack of baffling from the head allows oil to be sucked up as I've seen this on other engines with internal pcv. I'll probably completely route the pcv pressure externally and modify the valve cover with correct baffling at some point to decrease the amount of oil being sucked up.

[wstefan20]

UPDATE!

Tried to edit my original post, but it won't let me, so here's an update for all you f-body intake guys out there!

Setup is really the same exact one as the L36(na)/L26 where the "front" head is the pressure side and the "rear" is the intake side. Good news though is that the fbody engine's have the oil fill on the "rear" head stock, so you can plug your throttle body intake if desired and simply run fresh air in through the oil fill cap or to a catch can. Make sure you take note though of which head is which using the diagram because if you've switched the valve cover gasket position you could be in trouble.



Also wanted to use this to make a point. Had someone on the fiero conversion forum ask for pcv advice and everyone was telling him to come out the oil cap for any setup. The problem with this is that if you're using the f-body intake or L36 heads and your valve cover is on the "front" side, what you've done is made the front and rear head both the intake and exhaust. Basically, it will "work", but you're not cycling fresh air into the other side of the engine or the lifter valley so you're kind of defeating the purpose of having pcv altogether.

Anyways, hope that helps! As always, feel free to post questions.

[wstefan20]

UPDATE!

Tried to edit my original post, but it won't let me, so here's an update for all you f-body intake guys out there!

Setup is really the same exact one as the L36(na)/L26 where the "front" head is the pressure side and the "rear" is the intake side. Good news though is that the fbody engine's have the oil fill on the "rear" head stock, so you can plug your throttle body intake if desired and simply run fresh air in through the oil fill cap or to a catch can. Make sure you take note though of which head is which using the diagram because if you've switched the valve cover gasket position you could be in trouble.



Also wanted to use this to make a point. Had someone on the fiero conversion forum ask for pcv advice and everyone was telling him to come out the oil cap for any setup. The problem with this is that if you're using the f-body intake or L36 heads and your valve cover is on the "front" side, what you've done is made the front and rear head both the intake and exhaust. Basically, it will "work", but you're not cycling fresh air into the other side of the engine or the lifter valley so you're kind of defeating the purpose of having pcv altogether.

Anyways, hope that helps! As always, feel free to post questions.