The K&N Cold Air intake is a must for all WRX owners who love performance! This ingenious, washable cone filter is easily installed by any DIY mechanic in about thirty minutes. The results are dramatically improved engine breathing, especially at high revs.
The name brand K&N kit is the best way to go for easy installation and guaranteed-fit setup for your specific model, in this case, the 2004 Subaru WRX. Many other companies are in the cone intake market but K&N was the real innovator in washable performance filters. Typical performance gains are in the 5% range, taking our sample WRX from 222 to an estimated 233 horsepower. A K&N cone filter is critical to extract maximum gains from other mods, like larger turbos, downpipes, and exhaust systems.
The first install step is to unbolt and unscrew the OEM airbox and associated tubes. The kit includes a larger intake pipe that runs from the cone filter to the engine. Within here, there is a MAF sensor install point. Your OEM MAF (mass airflow) sensor will unscrew using an Allen wrench and is a direct fit into this new intake pipe.
Once installed, Subaru’s in particular get a much more baritone rumble and a pronounced intake snort on acceleration.
Here are some photos from my install on a 2005 Subaru Legacy.