What is the purpose of a crankcase breather/filter?

Can someone educate me on this subject? :headbonk: I am currently running a JLT catch can on the passenger side (which sees the most oil), but I was debating on buying a cheap crankcase breather for the driver's side. My car is N/A.

Is it worth picking up a crank case breather? Do I need to change anything relating to the tune to use one of these?

I see pictures of them all the time, but nobody ever explains what they're for and how they improve performance.

i had one. Shaun at AED told me to take it off asap. Take that for what its worth.

Bump for more info.

Personally I wouldn't run a breather on one side and catch can on the other. They bleed pressure differently and will probably result in different amounts of crankcase pressure on either side. I'm OCD and anal though lol.

Catch can, or the factory PCV system, re route the crankcase pressure into the intake. This way the intake vacuum pulls the pressure out and it's recirculated in a closed system (emissions). A Catch can simply puts a can in that line to catch the oil vapor from the crank case so it doesnt get sucked into your intake.

A Breather is basically just like removing the PCV lines and leaving the crankcase open. The breather filter is just on it so oil doesnt splash out and debris dont get inside. The crankcase pressure is just naturally released through the open breather. This is not done stock for one reason of emissions, and because the breathers will be saturated with oil after some time and have to be cleaned. Better system though IMO, zero chance of getting any oil into your intake. I would just put breathers on both sides.

I always run breathers

I was told on these cars the vast majority of NA and moderately boosted applications are fine with "catch cans" or oil separators. They are a good idea to ensure you do not have oil mist making it into the combustion chamber lowering effective octane, and maybe making the top side of the TB / Intake dirty. Once boosted UPR for example recommends a better one way valve to ensure under boost the pressure does not become an issue. There are several full out race shops that push enough boost they swear by breathers to remove as much pressure from the crankcase as possible. These engines spend a lot of time under boost and they feel the standard system cannot relieve the pressures that the engine will see, ultimately effecting ring sealing and longevity. If you were to run a breather on the car I would think it must be done on both sides so as to not introduce different AFR behavior. I have had two malfunctions on the driver side separator and they both were big ass vacuum leaks. Opinions seem to be all over the place. I would call someone you trust and ask them based on what you do with the car.