How To: NRG Catch Can in a 2005 Subaru STi

A catch can is a small container, that collects oil blown out of the PCV valve or valve cover intake hose (blow-by). The idea is to keep the oil out of the intake, which helps keep the intercooler running at maximum efficiency. This is because there is less oil vapor condensing on the inside of the intercooler. It is necessary to periodically empty the catch can to prevent it from overflowing. Some cans provide a drain for this purpose.