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Catch can with or without breather?

WL2005HBD

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Hi,

Just trying to understand why some catch cans have a breather, and why some don't?
My understanding is that the PCV system. Which draws blow-by back into the manifold to burn in the combustion camber, requires SOME kind of vacuum, so how the hell is a catch can with a breather beneficial?? Wouldn't this just cause a giant vacuum leak?
and, if the filter is one way (e.g can only exhaust fumes, not intake), doesn't this defeat the purpose of the emissions system and technically make it a draft tube, which from my understanding has been illegal for decades?

Which should I go for? Non-breather or breather?

Also, should be installed somewhere between PCV valve and the intake? (the nipples on either side of the manifold)

Thanks guys,
 

richardpalinkas

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A breather tank just allows the the crankcase pressure to find its way out of the least restrictive part. Normally both rocker covers go to a catch can then a breather on top. The ports on the manifold and intake pipe are then usually blocked off so there is no more crankcase entering the intake at all.

The downside from my many hours of research is that condensation and blow by products in the crankcase are not drawn out, so oil quality diminishes and requires changing more frequently.

The best way to set up a catch can is actually to use 2 of them, one for the breather side and one for the pcv side. This way, the original routing of the pcv system is intact but catches oil from both sides while allowing the manifold to draw out these crankcase pressures. A company in the USA called saikou michi make a dual can and can custom make them for your application, they have very good reviews along with the elite engineering catch can.
 

Jesterarts

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Short answer; without.

It's illegal to run a vented one on a road car.

Not sure what the point of a vented one is to be honest, but I do know the ELITE can I had on my old VZ clubby did the job well.
 

richardpalinkas

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I thought this too, but for some reason the last sc magazine said vented is roadworthy, sealed is illegal?
 

Big-Al

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They got it round the wrong way then. Vented is illegal because it bypasses the anti-pollution system. I.e. releasing crank case vapours into the atmosphere.
Sealed is fine as the gases are still vented into the intake and burnt in the combustion process. The concept of the catch can is to allow oil mist to congeal inside the can and be collected for disposal at the operators convinience rather than being burnt and lowering the engines tolerance to knock.
 

WL2005HBD

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I'm just wondering how oil ends up in the breather side to begin? Unless negative pressure is pushing oil vapours back out of the breather side into the piping > into the intake/Maf
 

VR38

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I'm just wondering how oil ends up in the breather side to begin? Unless negative pressure is pushing oil vapours back out of the breather side into the piping > into the intake/Maf

The PCV side has a variable system to it's design, it only operates on idle and low mid cruise applications, to prevent overpressurising the crank case at WOT the system reverse flows to thru the inlet.
 

richardpalinkas

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As said above, it can reverse flow during high rpm
 

WL2005HBD

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As said above, it can reverse flow during high rpm
Ahhhh makes sense
May invest in 2.

But which is more important for first placing? Pcv side or intake?
 
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