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The new "definitive catch can" thread

 
Old 03-30-2019, 11:04 AM
  #41  
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Why doesn't anyone run the exhaust side VC port to their turbo inlet? I run mine that way so as boost builds, the PCV shuts, then the turbo is pulling a vacuum on the crankcase. By running a fresh air breather isnt the crankcase just going to atmospheric pressure and not staying in vacuum? The purpose of keeping the case in vacuum is to help pull the rings towards the walls.

Not to mention that when running a fresh air inlet style filter or tank on the valve cover you are essentially creating a vacuum leak at idle.

IMO the best option is to run two sealed cans. One on the intake side, the other on the VC to inlet side. This will keep moisture/oil trapped in the cans while preventing vacuum leaks.

Another option is the down draft style. Run a pipe from your exhaust/down pipe at an angle and a hose to your VC inlet. The exhaust will pull a vacuum if done properly but can cause some slight smoking and failing emissions.
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Old 03-30-2019, 11:09 AM
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Originally Posted by L337TurboZ View Post
Why doesn't anyone run the exhaust side VC port to their turbo inlet?
I assume cause you want your turbo impeller clean. I would not want oil droplets hitting impeller blades at 150k rpm
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Old 03-30-2019, 11:24 AM
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Originally Posted by HarryB View Post
I assume cause you want your turbo impeller clean. I would not want oil droplets hitting impeller blades at 150k rpm
Of course. Thus the purpose of the second sealed can between the VC and turbo inlet.
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Old 03-30-2019, 11:32 AM
  #44  
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Originally Posted by L337TurboZ View Post
Of course. Thus the purpose of the second sealed can between the VC and turbo inlet.
No air / oil separator is 100% efficient.

And, not only do you not want oil mist hitting the compressor blades, you also don't want it getting into the intercooler, where it will condense into liquid and coat the inside of the tubes.
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Old 03-30-2019, 11:37 AM
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Originally Posted by Joe Perez View Post
No air / oil separator is 100% efficient.

And, not only do you not want oil mist hitting the compressor blades, you also don't want it getting into the intercooler, where it will condense into liquid and coat the inside of the tubes.
I agree. One option not considered is a vacuum pump. GM makes them for a lot of vehicles. Not to be confused with their Air pump which are for cold start emissions.
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Old 03-30-2019, 02:01 PM
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Yea, no one in this thread has mentioned vacuum pumps already. >.>
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Old 03-31-2019, 07:34 PM
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Like nearly every single answer/comment on this website: it depends.

OEM (MSM) runs a type of catch can (ish) and drains the fluid back into the oil pan and returns that "cleaned" air back into line just before the MAF.

But in the case of higher horsepower (=more blowby) builds, you'll be sucking that poorly filtered air back into the turbo and everything else. Not saying it's impossible to clean it all out. But you'd need a really good catch can or maybe more. Twice now (different setups) I've had issues with blowing loads of crap into my intake. Until I can make a bullet proof catch can, I'm not going that path again.

Yes it helps to pull a little vacuum on the crankcase, but isn't anywhere near enough to make a difference in power. From what I've read, you need 12-14 inches of vacuum (a lot) to generate more power, but to truly take advantage of this pressure differential, you'd need to install thinner rings to reduce friction losses.
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Old 03-31-2019, 09:46 PM
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Would a check valve between the intake and catch can help, such that air can only be under vacuum from the intake? And no oil vapor being drawn into the intake tract.
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Old 03-31-2019, 10:09 PM
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That would be a disaster. As soon as you produced more blow by pressure than intake vacuum, you'd close off the valve and blow every seal in your engine.
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