Hi guys just wondering what’s the options out there for a catch can setup for a turbo ls2.
Ive heard mighty mouse are very good but by the time I get it shipped over to the U.K. it’s a lot of money.
Has anyone made there own setup with an eBay can and how have you all got it routed?

 

Disclaimer, I'm a cheap SOB but I'm pushing 20+ psi through the setup I made for like $50, I am very proud of it. Before you ask I did this so long ago none of the links I have work.

Sooo I used an ebay catch can that came with a breather, bought a medical breather check valve and it seems to be working great. I also have a 10mm check valve between the can and the intake to prevent boost from pressurizing the system, just like in any PCV MM can. I have a -10an line coming off the valve cover to the can and I think it was a 3/8" hose between the intake and the can.

Also it's small enough I routed the hoses behind the battery and secured the can to the fender liner, I don't have any photos though.

I 'ported' the breather, and epoxied the check valve in place.









Routing(them paint skills):

 

Thank you so much for your help. Can I just ask a couple of questions please
-can you route to the already port on the valve cover instead of the oil fill? Why do people go from the oil fill?
-what is the purpose of the valve under the filter? I understand the one in the line to the inlet.
-did you just blank off the valley port and passenger valve cover port and run the driver valve cover port to the engine air filter?

 

Yes. I have the valve cover's ports blocked off, I used the oil fill just because I just wanted to run 1 big line instead of two, no reason for it.
Check valve, so when your engine isn't in boost it keeps closed so that the motor pulls the air from the valve cover into the catch can. When you're in boost and the check valve from the intake closes(so you don't pressurize your crankcase and blow a main seal) the valve on the can opens allowing the valve to vent through the can into the filter.
Yes, I ran the valley one into the air filter of my blower.* So it'll take in fresh air but won't pressurize in boost. You can do it with either valley or the passenger valve cover.

 

Thanks again.
So could I just run a check valve in the line between oil feed and can instead of in the filter? I’m struggling to find that type of valve you posted.
So I would end up with a check valve in each line

 

Haha yeah seems weird.
so Would it work the same with 2 check valves on the lines?
check valve between oil fill and can and a check valve between intake and can

 

Yea kinda I guess, but when the motor is pulling vacuum, it'll be pulling from the catch can vent instead of the valve cover, which is why I put a check valve on the breather so all the vacuum pulls from the crankcase.

 

I see what your saying. I’m new to this so struggle to understand it all.
I did draw it out and see that I can’t put a check valve in the hose between oil fill and can as that way it won’t allow fresh air to return to oil fill.
Maybe the only way is if I put the check valve between can and breather on a short hose. Please excuse the rubbish drawing

 

Yep that's exactly it. If you can't find the big check valve you can use a 3 port can and use one of the ports for the breather, then you can just use a check valve in that line. The only change in the diagram you have is there would be a line going to the breather instead of it sitting directly on the can.

 

there is an issue with this drawing. The line coming off of the drivers side cover to the blower inlet is going to suck oil through it. The vacuum needs to be pulled through the catch can to prevent the oil being sucked back into the s/c or turbo inlet. I would eliminate the line from the intake with the check valve and move the line from the s/c or turbo inlet to the can directly.

 

Goodness I hope there isn't that much of a vacuum, the line off the drivers side will be pulling in fresh air, going through the cc and being sucked out through the oil fill into the can and then back into the intake.

 

Let me clarify, I don’t mean it will be sucking straight oil, it will be sucking contaminated air from the motor which will include oil vapors that will collect and eventually puddle into oil.

The majority of your crankcase pressure is going to build up when the motor is under boost. When there is boost the check valve coming off the intake manifold is going to close. (Pretty sure we agree up to this point). So when the check valve closes the only place for the crankcase to vent is either through the vent in the catch can or through the line going to the supercharger inlet. The line going to the supercharger inlet is going to be under vacuum because of the supercharger sucking in as much air as it can so it will be pulling the dirty air from the motor. Over time you are going to get oil accumulate in that line and in the inlet of the supercharger.

 

If i'm understanding that's no different than having breathers on the valve covers except maybe some oil will accumulate in the can, there would be no vacuum to pull the air in/out of the cc.

 

Someone else replied to me saying this would be better

 

I Don't like this method because it depends on the check valve to open to save the engine everytime it goes into boost.
If that check valve ever fails, there will be serious problems.
Also the line lengths are undesirable. Anytime you add length of lines (volume) i.e. catch cans and addl volume of tubes, it weakens the effectiveness of PCV pressure drop.

I'm not saying its terrible, just not something I would use because I don't like systems with weak spots or failure points, i.e. excess complexity, unwanted additional components, etc...
The ideal method would be something like the original picture. Yes the pressure drop at the pre-compressor (post air filter) is going to 'pull' on the crankcase during boost and it will contain some oil component. Yet this is the method chosen from the factory for every turbocharged car. They use a somewhat convoluted tube with an appropriate PCV restrictor in-line (I can provide picture and details of the function if wanted) but overall you just take the intake tube off once in a while and wash it out is all. On turbo cars I also take the compressor outlet tube off and wash the compressor wheel with the engine running, for engines with 120-180,000 miles that have that slight buildup. The main point here is that the factory baffle in the valve cover, at the crankcase, shouldn't be so bad that it wets the intake tube with oil. If it does then either the baffle should be updated, or a free-flowing catch can in-line can be used for engines with damage (lots of blow-by). But no healthy engine should send oil into that tube under any circumstance to begin with.

 

This is a factory turbo car flow for cruise/idle (intake vacuum situation)
'

 

so by this drawing the line coming off of the turbo (pre filter) is positive charged? How does that happen?

 

I'm not sure what you mean positive charged. However I can explain more fully using easy to understand terms.

The crankcase during vacuum situations is connected to intake manifold. The intake manifold during vacuum situations presents the crankcase with approx 10-20" Hg of vacuum during normal idle/cruise situations.

The crankcase is subjected to such differential of pressure, however, for a variety of reasons, the crankcase maximum tolerable vacuum for wet sump applications is somewhere between 2 and 4" of Hg typically.
Therefore the crankcase requires a vent from which to replenish air molecules scavenged by intake manifold PCV in order to prevent crankcase pressure from dropping below 2 to 4" of Hg roughly

The volume of the crankcase is sized such that the diameter of pcv orifice, and diameter of fresh air vent orifice all work together to provide acceptable crankcase pressure signal during vacuum situations. It is possible to have both too much or too little crankcase pressure during operating conditions so this is a 'tuned' variable.

As to how it works in the above picture using numbers,
the intake section is approx 18" Hg, (14.5 - 9) = 5~psi absolute
the crankcase is approx 2 to 4" Hg of pressure, (10-12psi absolute)
the atmospheric vent tube (pre compressor) is approximately atmospheric pressure (14.45~psi)

So naturally because the highest pressure is inside the atmospheric precompressor tube, gas molecules will flow from the vent into the crankcase where pressure is lower.


Next we need to discuss the vent tube, pre-compressor conditions for boost situations but I gota do something atm

 

due to my lack of experience with turbo setups and not knowing what cam was being used for this test I cannot say weather your numbers are correct or not, but in a supercharged application that is more than likely incorrect. Although I don’t have numbers to support , I can assure you that the pre-compressor line with a supercharger is under vacuum not allowing fresh air to flow back to the engine. An exception would be where the cam was designed in a way that the valve timing events created high amounts of vacuum in the motor, which most blower/turbo cams do not have.

 

Well I assure you that the atmosphere is always atmospheric. Think about the air filter, what drives air into the filter? It isn't the supercharger- its the atmospheric pressure.

compressor of turbocharger = compressor of supercharger. Both units do the same thing. One is driven by a belt, one by exhaust gas. End result is the same.

Imagine you remove the filter from a running engine. What is the pressure in front of the throttle body or compressor? atmospheric. Now, run the engine at Idle, cruise, WOT, etc... What is the pressure in front of the throttle body/compressor? Still atmospheric. There is NEVER any vacuum in that region unless you specifically design the filter to be restrictive, which would reduce engine power.