Blowby gas is formed by air, exhaust, unburnt fuel, oil vapor and water vapor. Intention is to burn it in the engine by injecting it in the intake manifold instead of letting in the air and stink.
However, some of it and especially the oil vapor part being directed by PCV in the intake in certain conditions condensates in the intake manifold, and end up on valves and/or even on spark plugs.
Some of the newer cars with transversal engines have the intake manifold installed in front of the engine, right after the radiator and under engine's top level. In these air cools the intake (before the engine and radiator gets hot) more like for the intakes installed the other way around or "after" or "behind" the engine from the point of few of direction of air flowing under the hood.
Because these intakes are colder oil condensates in these more than inside the older types installed "behind" the engine.
Catch cans are empty cans with two connectors that allow some of the liquid fractions of the blowby gas to condensates in there before it reaches the intake. But there is a whole science behind those too and i (and many others) where not aware of.
Since catch cans get hot pretty quickly (depending on where the're installed) and are small in volume compared to the intake, they won't allow condensation of all the oil (oil is the most important cause it does not evaporate once it's in the intake or pools at the very bottom of it).
So what else allows condensation besides lower temperature? A drop on pressure does the same trick. (exactly like for the weather). So you have to add an element in the catch can which will drop a bit the pressure of the gas forcing the oil to condensates. (Like mountains in the direction of air flow, which allow clouds formations after air passing them).
Then you have to take care of the condensated oil and make sure it won't "shortcut" through the other connector by sticking something like a piece of metal between those.
The cheap can (25 bucks) i installed does not have such element. Or it has an empty one with holes at one end which are not enough. But i figured i might be able to fill that empty element with wires or washers (some use a kitchen metal sponge) to allow some increased resistance and create a pressure drop. But it's tricky cause pressure drop always restricts the flow.
So i went to Lowes and bought some braided picture hanging wire but also some small washers i will try to fill the empty separator in my cheap can. (A whole scene in there, with a giant cashier, maybe 8' tall and a Japanese woman half his height with red makeup on her face. He even said to her: Your nose is in my butt, could had been an allusion cause there was a very relaxing song earlier at the speakers and i was very... relaxed. It was done with my involuntary participation but the song was put by them. So she appeared red in her face next to the giant, magically, and he said that at that very moment).
Most advanced catch cans on the market are by far made by Mishimoto. Until last year they used a 50 microns sintered bronze element which to my opinion poses to much flow resistance. Still selling it for 100 bucks on Amazon, it had been copied by others already and it is available for under 20 (don't know about the quality though).
That was probably their opinion too cause last year they came with a new design, (what a coincidence, when i started to play around with those) and they call it "high flow catch can" but they won't say what material the separator or flow resistive element is made of. Some sort of oil resistant plastic (nobody other then them would dare to use plastic cause there is the danger of breaking and flowing... into the engine). Probably a protection from being copied again. That one is over 200 bucks.
A description of the older type here:
https://www.mishimoto.com/engineering/2016/01/blow-by-101-what-is-blow-by/
I suddenly figured out that the piece of sheet metal i put in the catch can does not allow expansion of the gas though condensation, lowering the volume by 1/3. I think it worked better without. I installed picture hanging breaded wire inside the expansion element and now it's ready to go. But it's too late, i will install it on car tomorrow. I put back the original PCV line.
But it is the first time today i realized it's not so simple. The catch can i have has too stages expanding element i now filled with packed wire. Just trying.
