What is a catch can?
A catch can is traditionally a can or container which captures oil that passes through the crankcase ventilation system of the engine.
Why do you need a catch can?
The crankcase of your engine has a one way valve which diverts excess gaseous air pressure from building within the engine. For emissions standards, this is directed back into the intake so that any harmful fumes or oils can be burnt off in combustion. The problem is that oil vapors will often condense in this process, resulting in liquid oil that can gunk up sensors, dirty intake valves, and result in poor performance.
This is especially bad on direct injectors cars, such as the FA20 WRX. With direct injection feeding gasoline straight into the combustion chamber, the gasoline does not have the opportunity to clean the intake valves. Given time, this can lead to buildup on the valves and preventing them from fully closing. Therefore, the purpose of a catch can is to help minimize this buildup; the only thing passing through the intake should be clean air.
These WRXs can actually utilize a dual catch can setup. One can mounted on the PCV (positive crankcase ventilation) line and one can mounted on the CCV (crank case ventilation) line.
In the world of performance tuning and track cars, it is recommended to have both catch cans or an AOS (air oil separator) system which feeds the captured oil back into the sump. But if you are simply seeking ways to extend the life of a WRX street car, a single catch can on the PCV line is usually sufficient; it is rare for the CCV line to see much oil on a healthy street build.
Which catch can should you buy?
Catch cans range in price from $20-$500.
Generally, the more you pay, the better the quality. Better internal baffles, better filtering, convenient level reading, easy emptying/draining options, plug and play brackets and hoses, etc. But the cheap universal catch cans often offer many great features at a very affordable price.
I opted to purchase this Universal catch can which is regularly found on Amazon for around $25. https://amzn.to/3AuX2Mr
The overall construction is surprisingly good.
The internal baffling is minimal but sufficient.
It utilizes steel wool as a filter. While this may not seem like much, a little bit of steel wool is enough for oil vapors to cling onto.
It even features a tiny dipstick, making it easy to quickly check the level.
Where this universal catch can falls short is in the supplied hoses are hardware. A custom bracket will need to be made for my application and the cheap rubber hoses are being thrown away in exchange for some nice silicone hoses and hose clamps.
Overall, there is nothing wrong with a quality universal catch can like this. Any sort of catch can system is better than nothing, which is made obvious once you see these simple cans begin collecting oil.
How to install on an FA20 WRX:
Remove the engine cover by releasing the plastic push rivets. Be careful not to break any of the tabs that hold the engine cover in place.
Remove the two intercooler bracket bolts.
Loosen the inlet and outlet hose clamps to the intercooler.
Remove the intercooler.
Locate and remove the factory PCV vent line.
Install the new 10mm Silicone hoses and secure them with hose clamps.
Mount the catch can in a convenient location of your liking. I opted to bolt it to the side of my intake box.
The “In” of the catch can should connect to the engine crankcase. The “Out” of the catch can should feed back into the intake manifold.
Catch can maintenance:
After a track day or hard driving event, I like to check the catch can level using the dipstick.
However, I usually only empty the catch can at each 5,000 mile oil change interval. Be certain to monitor your catch can levels regularly and empty as necessary. It is vitally important that you never allow your catch can to overfill, as the intake could begin drawing in liquid oil.