2G Catch Cans, Crankcase Pressure Questions

[kyler021]

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]

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

Hey guys. I am super new to working on DSM cars! I’ve always wanted an Eclipse and I finally bought one! I have basic mechanic knowledge but when it comes down to real performance I’m pretty green. So my first question on here is I just bought this car. It was supposedly built by a reputable...

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[kyler021]

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.

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?

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]

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]

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]

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]

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]

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]

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