So what are these cool catch can things, and why do all the fast cars have them? Okay so in your engine, you have the guts and all the black magic that happens inside when all the components are working together. As your piston moves up and down, sometimes combustion will make its way into the crankcase of the engine. The combustion happens on top of the piston, so you have air and fuel that gets into the crankcase which causes pressure. This pressure contains air, oil, as well as fuel and causes what is called "blow by".
Most vehicles are equipped with a Positive Crankcase Ventilation Valve (pcv valve) which allows the blow-by to escape. And usually, the PCV system is routed back into the intake. So now the contaminants getting pulled by the PCV valve are getting routed back into the intake where it ends up getting sucked into the intake valves which will create a buildup later on. Now you have to resort to either buying a fuel system cleaner on a regular basis or in some cases getting the intake manifold pulled off and getting the ports walnut blasted.
This can all get prevented with the use of a catch can. the catch can re-routes the air, oil, and nasty stuff back into the catch can rather than getting sucked through the intake. Catch cans typically have a filter and baffles so that only air will go back into the intake. This prevents knock in some cases, but you are greatly reducing carbon buildup on your valves and pistons for a cleaner operating engine.
RallySport Direct carries a wide selection of catch cans that are vehicle specific or a universal fitment. Choose from many great styles brought to you by Cusco, Mishimoto, Beatrush, and JBR. We have all different types, in different finishes as well with different tank designs, and with or without oil baffles.
For the Subaru bros, also consider upgrading to an air oil separator to keep that oil routed where it needs to go and be sure to check out the rest of our oil control devices and keep your engine running for as long as possible.