Hello,

I've been reading a ton of threads about how to properly set up an oil catch can in the FD. As you might already know, the PCV valve is practically useless in our cars since there is already a "natural" burning of exhaust gas. This is due to the slight overlap of the intake and exhaust ports in our engines, which virtually creates a PCV effect. This is why we don't see the PCV valve in '95 cars.

Now, here's where I'm having a hard time figuring out if I should have a line connected from pre-turbo to the filler neck so the crankcase can see constant vacuum and keep the engine seals happy. I know it's not true vacuum since it's not post-throttle butterflies, but in theory, there should be some "sucking" because of the resistance in the Greddy air filter I'll be using. Also I would put a one-way valve to keep oil out the compressor of the turbo.

I made a picture with Microsoft Paint to illustrate the routing. Also, my car is a street car, not a race car.


Is this a good idea or pretty useless?

 

On second thought, I wonder if anyone has considered T'ing into the vacuum chamber for the sequential setup instead of using the plastic turbo inlet. Obviously, you would put a check valve/one-way valve in place, but that would provide a much better vacuum for sure.

 

The first line with the arrow is how its set up from factory just without the check valve. The second line would go to a vented catch can. When using the twins, what you have pictured is really all you can do.

The line from the intake isn't really necessary. I get what you mean by "vacuum" but its not going to assist in the way that you think. You only need the one line from the neck to a vented catch can to achieve what you're going for. 1 -10 or -12 will be sufficient.

 

Got it, I'm glad I got the oil catch can routing correct, but it's a shame the "vacuum" from the turbo inlet won't assist as I had hoped. I remember reading when Dale Clark mentioned there's barely any vacuum pre-turbo, which makes sense. I was hoping to explore uncharted territory by supplying the crankcase with vacuum from anywhere in the vacuum chamber path in the sequential turbo system.

Below is the best picture I can find until I get home, but there is a page that shows which hoses are vacuum and which are pressure (purple is vacuum, pink is pressure). If I can tap into any of the vacuum lines, maybe this will help provide the crankcase with true vacuum. I like the idea of having a crankcase with negative pressure because I've read it has several benefits, such as less stress on gaskets and improved overall reliability.



This is really a reliability mod that I want to add, and we all know reliability mods are the way to go with these cars. Using vacuum from the vacuum chamber ensures a consistent and reliable vacuum, which could be good or bad. I haven't heard of anyone else doing this, but I'm afraid it might cause too much vacuum and/or take the load away from the solenoids that need the vacuum. Below is a list on why I'm so persistent on adding vacuum.

1, Reduced Oil Leaks: Lowering the pressure in the crankcase minimizes the chances of oil leaks by reducing the pressure that forces oil past seals and gaskets, helping maintain a cleaner engine operation.
2. Less Windage Loss: Decreased crankcase pressure reduces resistance against the rotating components, freeing up horsepower that would otherwise be lost to internal friction and improving engine performance.
3. Better Oil Control: Maintaining a vacuum helps in controlling oil mist and vapors within the crankcase, reducing the chances of oil contamination in the intake tract and keeping the engine internals cleaner.
4. Improved Engine Efficiency: With less energy wasted overcoming internal pressures, the overall efficiency of the engine is improved, potentially leading to better fuel efficiency and performance.
5. Enhanced Reliability: By reducing internal pressures and controlling oil mist, the engine operates more consistently, leading to enhanced overall reliability and longevity.

For better oil control, having a clean intake tract is the main reason why I wanted to install a catch can. If my theory is correct and supplying a better vacuum source works, then having a catch can might not be necessary. I might have to be the first one to try this but thought I’d share my idea.

 

Just got home and whipped up some editing in photoshop to show the vacuum/pressure in the sequential turbo setup.


Original diagram from Mazda


"The overlay that folds out to the right shows the pressure (boost) chamber and hoses (magenta colored). The purple is for the vacuum and storage system and hoses. All of these hoses maintain pressure or vacuum, based on the performance of the check valve. To illustrate this, these hoses change color at the check valve."



All I need to do is tap into one of the magenta colored hoses and connect it to the filler neck, in theory this should be true vacuum compared to the turbo inlet nipple. Again, I would place a check valve in the new hose so your crankcase isn't pressurizing your vacuum.

Any feedback is welcome, I'm only trying to bounce ideas around.

 

I realized as I was laying down that the vacuum stops at the check valve, so this whole idea is pretty useless, oh well I tried. At least I provided a neatly edited diagram of the pressure/vacuum diagram.

 

Is this a street car or are you going to track it?

 

Once you're under boost, you are going to have far more positive crankcase pressure than any form of vacuum created by tapping into the intake manifold or pre-turbo.

You really need a dry sump to realize any form of gains that you're looking for.

Also, venting the oil fill tube to atmosphere with a catch can would negate any form of vacuum created in the crank, even if you had a dry sump.

Under boost, you're going to be pumping a lot of air into the catch can and out of the catch can vent filter.

 

I agree that no amount of vacuum created by the air intake system or engine vacuum could even remotely overcome the boost induced positive crankcase pressure, particularly on repeated short-term boosting. Engine vacuum is only like 6-7 psi at idle and air intake vacuum is less than 0.3 psi at idle (which you would have to store prior to boosting for either) and the evacuating vacuum line on the oil neck pipe is only 8 mm in diameter. In my opinion on a stock or more stock twin turbo, the reason I use a non-vented or vacuum assisted catch can with slight vacuum from the stock air intake neck on the primary turbo vs. a vented catch can, is during the non-boost times. Even though I believe this is small, the positive crankcase pressure after coming off boost can be relieved faster by some vacuum rather than no vacuum (atmospheric pressure of a vented catch can). A vacuum assisted catch can, on repeated boosting in shorter time frames, such as a road course or aggressive street driving, can lessen the chance of more continued high positive crankcase pressure more than a vented catch can, can. Also, the vacuum assisted catch can, can keep slight vacuum all the time on the crankcase during idle and cruising, helping to keep any potential positive pressure down.
Mike

 

​​​​​​That might be true if the vent line from the crank to the intake neck is big enough to not cause a restriction. The negative of this is pumping a lot of oil into your intake system, filling the turbo, intercooler, and engine with oil which increases carbon buildup in the engine and is more prone to detonation.

Road racing on twins is a challenge, especially when taking right hand corners where the oil fill tube becomes blocked with engine oil and crankcase pressure pumps a ton of oil out of the fill neck and into the catch can (or air inlet in your situation). Single turbos with venting the rear iron via the turbo drain hole greatly improved this problem, but it's still a challenge to manage all of the crankcase pressure and oil that gets pumped into the catch can.
​​​​

 

In my post, I am not advocating for not having a catch can on the stock vacuum line configuration. That's why I have one. I agree the vacuum line is small, at 8 mm as I stated, which does cause restriction. With using WMI as many of us run, any carbon buildup would be minimized with the catch can in place trapping most of the oil. A quality (not a cheap knock off brand) catch can will trap most of the oil and potentially only let a small amount of oil vapor back into the turbo. The other options are deleting the stock vacuum line, which is far worse for crankcase pressure with all the negatives previously stated for high pressure in the crankcase or no catch can at all, far worse for oil blow back into the air inlet and turbo.

I have some anecdotal evidence about the use of an oil catch in a mostly stock twin setup. I am in the middle of installing a new engine and have the major engine bay components out of the car. I have had a quality oil catch can in place for years on a mostly street driven car with a few road course days in a five-year period and have zero oil film on the inside of my primary turbo intake pipe, my air intake crossover pipe, or my intercooler inlet pipe.
Mike

 

Thanks for the replies guys, helps me decided what the hell I'm going to do. With what mikejokich is saying, the new routing should be like this?



My car is not a track car and it’s on stock twins. I believe that some vacuum is better than no vacuum or using an atmospheric pressure/vented catch can. My main concern was getting blow-by in the oil neck pipe for the primary turbo, but if you haven't had any oil inside the turbo with a quality catch can, then I'll do the same setup. I'll be using the discontinued Greddy catch can that you see in the picture above, not the cheap replicas you find on Alibaba.

 

If you're only driving on the street, I wouldn't worry much about it. The factory setup is even fine.

You shouldn't really be puking oil simply under boost. The oil puking happens on track, particularly with really sticky tires, where the slosh leaves nowhere for the pressure to escape so it gets expelled with the air. I have a -12 line to a vented catch can, and I've rarely ever put a drop in it on the street, whereas I'll fill 1qt can in a 20 minute session.

 

@ptrhahn Wow! What it is it getting filled with - oil or watery stuff?
If oil, this would mean you add a quart after each session?

 

It's oil. I let it run a half a quart down (once it pukes it out from completely full), and then I'm adding 1/4 to 1/3 of a quart per run. A LOT of this is the fact that the oil pan on the FD is shallow, so the oil line at full is above the pan seal and in the motor block itself. Letting that fist 1/2 quart out helps a lot.

 

When I've run the vacuum line to catch can using the twin-turbos, it worked fine. On big single turbo, running vacuum would fill the can up on a short drive and after disconnecting back to normal few ounces collected between oil changes.

Jack

 

Well, after receiving my GReddy can (On the right in pictured above), I realized it’s just a universal brand with GReddy written on it. Brands often do this, including FEED and many others, which is expected. Unfortunately, the can GReddy chose lacks any baffling or steel wool inside. I’d like to use this can since most of my engine bay is GReddy. Any ideas on how to modify this can on the right? Know of any kits to make it perform like a proper catch can? Thanks.

 

Nevermind, I found a solution that might help anyone interested in the future. Hopefully, the link isn’t dead by the time you see this. Here’s an example picture from the link.

https://www.evolutionm.net/forums/ev...nlet-tube.html

 

On my FC I tried a vacuum vented catch can with steel wool and check valve.

With stock oil pan it would still slosh oil up the filler neck which would get sucked up into the intake tract.

Racing, it also sucked oil even after I put a mazda competition oil pan in with RB oil pan baffle (but fine on street).

I ditched the vacuum line and went with passive vented catch can and iy kept my intake tract oil free.

My FD experience was the same. With the Winchester trap door baffled pan a passive catch can will stay dry of oil and just collect water and gasoline.

If you absolutely need vacuum and dont want oil in the intake tract the "racers" way is to do an exhaust scavenge vacuum system.

 

if you're racing, there is enough force to put oil in places you wouldn't expect. back when the Spec E30 series started a couple of people lost engines because its a slant 6,
so turning one way its fine, but you turn the other way, and all of the oil runs uphill to the valve cover.

if you're on the street its just not a thing

 

Thanks for all the replies again, everyone. I'm not racing, but the main reason I'm looking into a vacuum setup with a catch can is to reduce stress on the engine gaskets. My goal is to make a "reliability" mod by providing vacuum in the crankcase. One common gasket that tends to fail is the oil pan gasket since oil sits above the oil pan. I've already replaced the gasket using Hondabond (the best RTV available) and installed an Elite oil pan brace. Their design includes "rib" cutouts, which prevent the oil pan from being crushed. Crankcase pressure can make an engine leaky, but vacuum will help prevent most leaks.

I think I might just buy a universal vacuum reservoir and connect check valves to it from the manifold, similar to our OEM vacuum reservoir, but as a separate system from the twin turbos. This way, I can provide vacuum to the crankcase effectively.

New idea:

 

Forget the idea above, too much vacuum can mess with oil pressure, and I'm not risking these pricey engines just to experiment.

 

I used crankcase vacuum to stop turbo oil seal smoke at idle on my FC (race oil pressure regulator problems). So, you can exceed combustion pressure leakage at idle into the sump with engine intake vacuum as you plan.

No idea about keeping ahead of combustion leakage into sump at high combustion pressures and side housing thermal distortion under load.

Then when I rebuilt that FC engine I used the non-checkball rotor oil cooling restrictor jets to lower oil pressure at idle which stopped the smoking and I deleted the vacuum to sump because I could never keep oil out of the intake tract with it.

Oil pan seals... thats another issue.

Only oil pan I ever had not leak was Winchester Metals (Bacon) pan on my FD. That 1 of 10 for me (yes, had pan braces as well).

 

Added my first accessary to my 'custom' catch can—a sight glass made of real glass and computer open-loop plumbing.

 

This is the type of setup I always run when I install them for many of the reasons others have stated. One thing you need to watch out for is catch can placement especially in high humidity environments. You want to place the can near the turbos if possible to keep the temperature in the can up. If you don't, the can will fill up with water due to the water vapor condensing if its in a cool enough location for water to become liquid again. I have this same Greddy catch can on the wife's car, has been on there for 20 years but the bay is so tight that I can't fit this particular can in a warm enough location to keep the humidity in vapor form. I plan to build a custom setup when I update the car. Because of this and me living in Florida now, during an AutoX day I have to dump the can twice, once after the morning session and once after the later session and it just fills with water not oil. It wasn't as bad when I lived in Dry Colorado but still noticeable. I catch very little oil in the can but have to regularly dump it for water even for street driving. When I am able to install these in the hotter parts of the engine bay, I don't have this problem.