QUOTE (wing_woo @ Feb 13 2009, 04:00 PM)
Basically, the excess oil that shoots out the PCV valve has a lot of gunk and it makes your intake manifold dirty. There's a thread about it in the Mazdaspeed6 section. This filters out the oil/air that goes through the PCV valve so you have cleaner airflow going into the IM...that's what I think it's for.[/b]
+1. Except it doesn't really "filter", in the sense that some filter material is doing it and needs to be cleaned out or replaced every so often, though some people do put steel wool and other similar fibers in their catch can. Just having the crank air, which is laden with microscopic oil globules (in an aerosol mist form) go through a labyrinth where the air velocity changes causes the oil globules to come together to form larger droplets and fall out of the air into the bottom of the canister.
If it's left in the air the oil enters the intake tract and can deposit itself in the nooks and crannies of the intake manifold and intake ports (just like it does in the oil catch can), as well as the back side of the intake valve. This oil is not the nice, clean oil that comes out of fresh can. Rather it's laden with byproducts of combustion and more like a sludge. The result is a build up of thick, blackish sludge inside the intake system, which can eventually impede air flow. Also, this oil doesn't help the combustion process if it's still in the air when it gets into the cylinder.
The Speed6 is especially sensitive to this because of the direct injection system. With conventional port injection, fuel is injected upstream of the intake valve. Using gas from companies like Chevron, which adds Techron to their fuel, helps to keep the parts of the intake system downstream from the injector relatively clean, because fresh gas with the cleaning agent is flowing over it constantly. Remember those ads showing the difference between the intake valve on a car using "regular" fuel vs Chevron with Techron?
The direct injection in the Speed6 squirts fuel directly into the combustion chamber, so no fuel with cleaning agent ever flows over the portion of intake port and intake valve that it would on a port injection engine. The result is no cleaning effect for the intake system or intake valves from using Chevron with Techron or pour-into-tank fuel system cleaners (though they would keep the other parts of the fuel system "clean" but I highly doubt that gasoline leaves any kind of deposits while traveling through a hose or tube).
So, any sludge that builds up on the back side of the intake valve on a Speed6 would never get cleaned off, no matter how much Chevron gas I put in or how many cans of fuel injector cleaner.
Will treatments like SeaFoam work on the Speed6, where the solvent is added into the intake tract, usually near the throttle body or a vacuum port on the intake manifold? Maybe, but I personally haven't seen how good a solvent SeaFoam is. I'd feel more positive results would be derived from using strong solvents like lacquer thinner or methyl hydrate, which are proven to break down oil, but I'm not sure how dangerous it would be to use volatile solvents of this nature near or in a fiery environment.