Resolved Catch Cans, Crankcase Pressure Questions

kyler021 · Wednesday at 4:56 AM

Hey all,

I'm hoping to clear up some questions/concerns/misconceptions I have about catch cans and crankcase pressure. I've read many threads on catch cans, The 4G63T PCV system thread that everyone points to when you have a question about catch cans, and I've seen some setups for catch cans firsthand but I need more clarification. Because of course, there is varying opinions all over the place and I'm not sure what's right and what's wrong. What the 4G63T PCV System thread says that you NEED to do in order for gasses to effectively escape the crankcase, someone does the complete opposite, and it seems to work fine for them. Anyways, I'm rambling so I guess I'll just get straight into it.

So, I've been having issues with crankcase pressure popping out the dipstick, AND blowing past the seal on the oil cap. Throwing oil literally EVERYWHERE in the bay. For context, this is about 18psi at 6k RPM, on an Evo 3 16g turbo. This is also with the "Improved stock PCV Setup", minus the check valve as seen attached to this post, and on the thread posted above. Running 2 catch cans, and I've made sure they're hooked up properly about 100 times. I have high oil pressure (10w-30) too, I think it was about 65psi at 3k rpm, if that matters. I'm not sure what it goes to at redline but I'm guessing more than 100psi for sure. I've done a compression test too:
Cylinder 1: Dry - 115psi, Wet - 135psi
Cylinder 2: Dry - 125psi, Wet - 150psi
Cylinder 3: Dry - 130psi, Wet - 135-140psi
Cylinder 4: Dry -130-135psi, Wet 145psi
I have a new PCV valve, new catch cans, and new valve seals. I think I'm going to try to leave the hoses vented with no catch cans and see if that helps. I can't do this soon though, because I need a new timing belt since oil got on it.

Here are my questions and concerns:
If my current setup, the improved stock setup, isn't helping with crankcase pressure, is it worth trying to go for a bigger catch can/tank setup? Will that even help/work?
If the rings are worn bad, will a catch can even work to help the oil blowing out the dipstick and cap issue?
Some people say not to run the vented cans (including that thread), some people swear by them. Why do you think they are not effective/effective?
Some setups don't have the vacuum source to pull gasses out, and they work well without it, even though that thread, and a lot of people, say you absolutely need it to have an effective setup. Why is this?
If the catch can I want to use is vented, do you still need that vacuum source to pull out gasses and blowby oil?
If I wanted to convert to AN lines for a catch can, what's the best way to run them? If I'm just running 2 AN lines on the VC, what do I do with that PCV nipple on the intake manifold?
I was taking a look at the Forced Four billet oil cap adapter, and was thinking about running 2 lines to vent from there to a catch can, instead of using the stock nipple locations for the PCV. Is that a good setup or bad idea?
If I were to do that, what would I do with the stock nipples? Just leave them vented? Or cap them?
If I get the AN fittings welded in the stock location, I'm assuming baffles need to come out? What size AN fittings would work best?

If anyone has pictures of their setups and what worked for them, that would be awesome. I know that's a lot of questions, even if you have the answer to one of them, I'd love to hear it. I'm trying to gauge opinions before The Shootout, so I know how much money to bring and what to buy. I probably have more questions that I can't think of right now, so I'll add them when I think of them.

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CKOPOCT · Wednesday at 6:48 AM

I think you have 2 issues going on that may be causing/contributing to your problem. The first is the lack of a check valve in your PCV system. Without it you are forcing compressed air INTO the ambient engine environment while under boost. The 2nd catch can (boost can) will relieve some of that, but not all of it. The turbo will push more air faster than the pre-turbo line will be able to vent. The second concern is the wet/dry compression readings on 1 and 2. At 20-25 psi difference you're looking at worn rings (which I think you already knew).

As to vented vs. non-vented cans: vented catch cans do nothing to draw the gasses out of the engine. They just keep the engine from building positive pressure. In your current state it would probably resolve the oil sneeze issue, but it wouldn't do much to eliminate the crap in the air inside the valve cover/engine.

I use the same catch can setup as in the picture, with the check valve. No problems. See post 14 in the following thread for my setup.

PCV valve

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kyler021 · Wednesday at 8:54 AM

CKOPOCT said:
I think you have 2 issues going on that may be causing/contributing to your problem. The first is the lack of a check valve in your PCV system. Without it you are forcing compressed air INTO the ambient engine environment while under boost. The 2nd catch can (boost can) will relieve some of that, but not all of it. The turbo will push more air faster than the pre-turbo line will be able to vent.

Gotcha. So hopefully once I grab a check valve, it'll actually do it's job? I think that makes sense in my case, because to my knowledge, it only would shoot oil out at around 18psi at high rpm, so my guess is that it vented good enough until then.

CKOPOCT said:
The second concern is the wet/dry compression readings on 1 and 2. At 20-25 psi difference you're looking at worn rings (which I think you already knew).

Yeah, I was afraid of those results. But I guess it's better to know for sure. Is this the point I should stop and think about an engine rebuild? Or try the check valve first and see if that helps?

CKOPOCT said:
As to vented vs. non-vented cans: vented catch cans do nothing to draw the gasses out of the engine. They just keep the engine from building positive pressure. In your current state it would probably resolve the oil sneeze issue, but it wouldn't do much to eliminate the crap in the air inside the valve cover/engine.

I use the same catch can setup as in the picture, with the check valve. No problems. See post 14 in the following thread for my setup.

That makes sense now. So I guess that should be a last resort for me, using a vented catch can. If I can't get it to stop vomiting oil I'll try that. Thanks for the insight!

diambo4life · Wednesday at 10:24 AM

Run a vented catchcan setup. We have literally been doing this for decades. If your car is still pushing the dipstick out aggressively with two -8AN sized vented lines from your valve cover, you have an internal problem. I don't think you should have done a compression check, a leakdown test would have been better as it would have shown you where the combustion gases are actually going and how bad it is

kyler021 · Wednesday at 3:27 PM

diambo4life said:
Run a vented catchcan setup. We have literally been doing this for decades. If your car is still pushing the dipstick out aggressively with two -8AN sized vented lines from your valve cover, you have an internal problem. I don't think you should have done a compression check, a leakdown test would have been better as it would have shown you where the combustion gases are actually going and how bad it is

I think the compression check was more about checking just how the rings were doing, since that's the only thing I haven't replaced yet. They're not doing so hot based on the wet compression results posted above. I don't have access to an air compressor for a leakdown test so that was my only choice. I may go ahead and grab a vented catch can eventually like you said. I just need oil to stay where it's supposed to. Thanks for the comment!

diambo4life · Wednesday at 4:15 PM

I am not a fan of the wet test because it can be inconclusive....that's all. It's really difficult to properly oil the cylinder walls with the head on without getting oil on the piston crown. You don't want any oil going on top of the pistons because that will alter the car's compression numbers and it may give you a false positive. You can also try and vent the block as there is a plug there that you can use as a venting port. I have never personally used it but I don't see why it wouldn't work.

jdxnc · Wednesday at 6:32 PM

As you said there's a lot of opinion on what is the "correct" way to do it, you can listen to all those opinion and form your own. I'm going to tell you what I did, when I street drove my car for 15 years, for nearly 100k miles and what worked for me.

Delete the PCV crap and run 2x -8an off the 2 existing holes in the valve cover, to a sealed catch can, with a single -10an return to the intake pipe, pre-turbo. I never had oil that smelled like gas, I never had moisture buildup under the oil cap, I never had smoking issues and I never had the dipstick pop out. This car was driven hard, a LOT. The last 8 or so years of it's daily driven life were at 40-42 psi, a car that ran 9.85 in the 1/4 mile but also drove to work the next day. This motor was built but was also beat, it had ~135 psi compression across the board, I dingle berried it and re-ringed it twice in it's life. It was by no means a motor in great shape but it never had any issues with crankcase pressure with this catch can setup. The block was finally retired in 2024 when it cracked a cylinder wall.

I don't care about anyone's theory on the correct method, I know what worked for me and this is what I would do for any street car in my hands.

TerminalTalon · Wednesday at 7:32 PM

The most efficient will be like factory but with a decent well designed catchcan in between but the ease of a vented setup with less lines and setup cost is also well noted for many high horsepower people. Once you start looking up like an Improved Racing setup it adds up fast. The can, valve, fittings, lines, running it all.

I’ve messaged NRE and he uses two Moroso vented normally. Does he see a recirc’d system working at that level. No. Mind you that’s on average 2000hp+ v8 setups. He knows engines

I’ve messaged Jay Meagher also.

“Hello. The venting of the crankcase and line size is dependent on the sealing of the engine/fuel type and engine wear.

Most engines will be just fine with two -10 lines.

What engine are you working on?”

He didn’t respond yet. He’s busy. He’s Jay Meagher. I think his experience is based off of many ranges of horsepower and crank pressures. At some point it’s either the engine is too loose or the setup isn’t sized correctly.

I’m personally in between both. The ease of just running two 10an to a JMF can seems simple. Running a recirc’d setup seems to always be more efficient especially for daily cars where you see wide ranges of vacuum and boost. Strictly drag vented is just the way and the engines are built loose. Many of those guys all go puke tank which also makes sense at a level.
I’ve been throwing a few back when I should be packing for the Shootout. Hopefully it’s understandable

chrysler kid · Wednesday at 11:38 PM

Just a personal gripe, I hate AN fittings on the valve cover. They don’t need to be threaded at all and are under zero pressure. The fittings are way too large for no reason and get damaged just installing them normally or removing them for maintenance. It’s a street car making sub 300 hp I don’t need huge ass fittings. I’d seriously rather drill and tap my own 3/8 hose barb fittings in the valve cover than spend $400 for a valve cover with two big ass threads welded onto it

Drill holes in the internal baffeling in the valve cover and run a T to the original port the pcv valve was installed on. Use the factory breather port and the pcv port ( with the pcv valve T’d ) to make a second breather back into stock intake tube or to a catch can.

I’ve also noticed engines with less than 140 psi in a cylinder will have issues blowing oil out of the dipstick or the oil cap. The oil cap design into the valve cover was always a weak design, should have been a threaded cap like literally every vehicle made has had in except our cars. I’ll usually get a new cap with a new o-ring and bend the crap out of the dipsticks metal tension arms

For the dip stick you can still buy a new oem tube and run a new oem 2g dipstick which has two o-rings to give more tension for the stick to stay in the hole. On all of my cars that popped them out a new dip stick or just new o-rings on the stick solves the problem. Usually on the 2g dipstick they end up breaking the handle because the dipstick stays in there so tightly that people switch back to a 1g dipstick

kyler021 · 2026-08-27T03:46:49-0500

jdxnc said:
Delete the PCV crap and run 2x -8an off the 2 existing holes in the valve cover, to a sealed catch can, with a single -10an return to the intake pipe, pre-turbo. I never had oil that smelled like gas, I never had moisture buildup under the oil cap, I never had smoking issues and I never had the dipstick pop out. This car was driven hard, a LOT. The last 8 or so years of it's daily driven life were at 40-42 psi, a car that ran 9.85 in the 1/4 mile but also drove to work the next day. This motor was built but was also beat, it had ~135 psi compression across the board, I dingle berried it and re-ringed it twice in it's life.

Gotcha! Did you use a custom catch can or do you have any recommendations for which style catch tank to buy? I couldn't find close up pics on your build thread of the catch can setup, but I did see those lines from the VC going over to the firewall?

TerminalTalon said:
The most efficient will be like factory but with a decent well designed catchcan in between but the ease of a vented setup with less lines and setup cost is also well noted for many high horsepower people. Once you start looking up like an Improved Racing setup it adds up fast. The can, valve, fittings, lines, running it all.

Yeah the setups I'm looking at are definitely expensive, that's for sure.

TerminalTalon said:
I’m personally in between both. The ease of just running two 10an to a JMF can seems simple. Running a recirc’d setup seems to always be more efficient especially for daily cars where you see wide ranges of vacuum and boost.

I guess there's just so many setups to use I just don't know which is the "correct" one to go with. Seems like I could do either one and be fine even though people say otherwise. Plus my engine is definitely tired so I don't even know if the catch can will fix anything.

CKOPOCT · 2026-08-27T06:06:46-0500

For my setup I just used Evil Energy's cans. They weren't very expensive ($38 on Amazon right now). The main reason I chose them is because I wanted the cans to be red, but more importantly I wanted to be able to add filtering media to the can (stainless steel wool) and have the can baffled to ensure as much of the oil and water in the vapors would get caught in the can. Several cans I looked at either wouldn't open or weren't baffled... or they were much more expensive than I was ok with ($150, $250, $400??!! It's a CAN for God's sake...).

As to a setup, you can't go "wrong." Vented or sealed. One can or two. PCV or no PCV. Hoses everywhere or one hose to rule them all and in the darkness vent them. You know how and why the PCV/catch can system works, so you just have to determine what you ultimately want and implement the system accordingly.

You should seriously consider an engine rebuild if your budget allows, though it may not be absolutely critical at this point (car still runs).

kyler021 · 2026-08-27T10:23:25-0500

CKOPOCT said:
For my setup I just used Evil Energy's cans. They weren't very expensive ($38 on Amazon right now). The main reason I chose them is because I wanted the cans to be red, but more importantly I wanted to be able to add filtering media to the can (stainless steel wool) and have the can baffled to ensure as much of the oil and water in the vapors would get caught in the can. Several cans I looked at either wouldn't open or weren't baffled... or they were much more expensive than I was ok with ($150, $250, $400??!! It's a CAN for God's sake...).

Yeah, these prices are CRAZY. It's like, yeah I'm basically about to $400+ on a soda can with steel wool in it.

CKOPOCT said:
As to a setup, you can't go "wrong." Vented or sealed. One can or two. PCV or no PCV. Hoses everywhere or one hose to rule them all and in the darkness vent them. You know how and why the PCV/catch can system works, so you just have to determine what you ultimately want and implement the system accordingly.

You should seriously consider an engine rebuild if your budget allows, though it may not be absolutely critical at this point (car still runs).

I keep going back and forth on this. Like 2 hours ago, I knew what I wanted, now I have no clue. I think I want sealed, then I want vented, then IDK. It's driving me crazy and I'm overthinking the whole thing. I definitely do need a rebuild, I just have no money for this car and the catch can situation definitely doesn't help me. I was thinking of picking up a split thrust block to build on the side at the Shootout, but now I have to get all this stuff.

jdxnc · 2026-08-27T11:36:51-0500

kyler021 said:
Gotcha! Did you use a custom catch can or do you have any recommendations for which style catch tank to buy? I couldn't find close up pics on your build thread of the catch can setup, but I did see those lines from the VC going over to the firewall?

The current setup goes to the rear of the car, as it's a dedicated drag car now.

For the longest time it was a simple Greddy style can that I added AN fittings to. I also added an interior divider along with some SS wool to help seperate the fluid, which it did very well.

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kyler021 · 2026-08-27T12:28:24-0500

jdxnc said:
For the longest time it was a simple Greddy style can that I added AN fittings to. I also added an interior divider along with some SS wool to help seperate the fluid, which it did very well.

Gotcha, and I see a fitting on the top there, is that for the vacuum I'm guessing? Asking because I was looking at a 4-port can and was wondering if I could use one of the ports at the top for vacuum and the other 2 for the actual PCV/oil.

I think I've figured out what I want to do? I'll get that check valve, like @CKOPOCT was saying, and get someone to weld on an AN bung to the STM SD Intake so I can run a -8an to 3/8 barb fitting for the pre-turbo vacuum. It'll still be the 2 catch cans I currently have, just with the check valve and pre-turbo vacuum hooked up. And I'll probably find a better way to mount the cans rather than just have them sitting around in the bay.

If that doesn't work, I'll get the Forced Four oil cap vent, run it to a vented catch can where my power steering reservoir used to be. If that doesn't work, I'll build a split thrust block. Does that sound like a decent plan guys? I appreciate everybody's input here!

jdxnc · 2026-08-27T17:24:13-0500

kyler021 said:
Gotcha, and I see a fitting on the top there, is that for the vacuum I'm guessing? Asking because I was looking at a 4-port can and was wondering if I could use one of the ports at the top for vacuum and the other 2 for the actual PCV/oil.

Correct, as I stated in my previous post it's a -10an to pre-turbo.

Stapl3 · 2026-08-27T18:08:06-0500

Mine is similar to what jdxnc described. I used rubber hose from the 2 ports on the valve cover to a simple sealed catch can, then to the intake pipe. I beat the snot out of this car for years and would drive for hours at a time. No smoke, dipstick issues, etc etc. Nothing.

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kyler021 · 2026-08-27T18:34:30-0500

jdxnc said:
Correct, as I stated in my previous post it's a -10an to pre-turbo.

Shoot sorry, don't know how I missed that in your first post.

Stapl3 said:
Mine is similar to what jdxnc described. I used rubber hose from the 2 ports on the valve cover to a simple sealed catch can, then to the intake pipe. I beat the snot out of this car for years and would drive for hours at a time. No smoke, dipstick issues, etc etc. Nothing.

Also I'm noticing that you guys don't necessarily go out and look for a 3 or 4 port catch can. You guys add them on there yourselves, do you just drill, cut threads / weld for a fitting then run the line to the intake? I guess I had never thought of that as a possibility.

Stapl3 · 2026-08-27T18:57:44-0500

kyler021 said:
Also I'm noticing that you guys don't necessarily go out and look for a 3 or 4 port catch can. You guys add them on there yourselves, do you just drill, cut threads / weld for a fitting then run the line to the intake? I guess I had never thought of that as a possibility.

The can I used was a cheap ebay one for like 15 bucks, it had the two top ports, I hooked those up to the valvecover. The third hose for the intake pipe I just drilled a hole in the catch can and threaded in a brass barb fitting. It couldn't be a more basic setup.

kyler021 · 2026-08-27T20:46:13-0500

Stapl3 said:
The can I used was a cheap ebay one for like 15 bucks, it had the two top ports, I hooked those up to the valvecover. The third hose for the intake pipe I just drilled a hole in the catch can and threaded in a brass barb fitting. It couldn't be a more basic setup.

That's awesome! Well thanks guys I think I get the gist now! There's a ton of different ways to do this and I guess none of them are technically wrong. Thanks for the info and ideas!

jdxnc · 2026-08-28T06:53:40-0500

kyler021 said:
Shoot sorry, don't know how I missed that in your first post.

Also I'm noticing that you guys don't necessarily go out and look for a 3 or 4 port catch can. You guys add them on there yourselves, do you just drill, cut threads / weld for a fitting then run the line to the intake? I guess I had never thought of that as a possibility.

When you have the tools you can do whatever you want, no need to stick to premade products, usually far cheaper as well.

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