The Mishimoto Baffled Oil Catch Can Kit is designed and engineered to eliminate harmful blow by vapors from re-entering your engine. The EJ25 in the STI is known for producing blow by gases during both normal and severe driving, especially when boost levels are increased. This oil blowby can work its way into your intake system, reducing the octane rating of your fuel and potentially causing damaging detonation. Detonation has a profoundly negative effect on the already sensitive EJ25 engine. The kit uses our small baffled catch cans with a bronze filter and internal baffle to better separate the oil from the crankcase vapors. The turbo inlet side of the kit utilizes our three-port baffled catch can to catch as much oil vapor as possible. It also includes two direct fit mounting brackets making this kit easy to install and applicable for both LHD and RHD models! The kit comes with six direct fit hoses that will provide durable operation and provide a factory-like appearance after install. The hoses are designed to fit right onto the PCV valve ports and the turbo inlet ports. Durable barb fittings provide connections between the hoses and catch cans. Like all of our products, this baffled catch can kit includes the Mishimoto's lifetime warranty! Our catch cans are different from most air-oil-separator (AOS) systems on a few levels. First, our catch cans are not heated. This means that all of the blow-by is able to condense in the can, including low-octane oil vapors and contaminated fuel vapors. Most AOS systems also drain the blow-by back into the oil pan, while our catch cans trap the blow-by and keep it out of the engine permanently. If you've seen what We've seen in the bottom of our catch cans, you won't want that draining back into your oil either.