The HKS 33006-BF003 Cattless Resonated Bellmouth Downpipe for the 08-14 WRX & 08-16 STi is 3" of mandrel bent stainless steel designed to improve exhaust flow. The bellmouth 33006-BF003 is an excellent option for your 08-14 WRX & 08-16 STi if you are running a stock or upgraded turbo and supporting tune. This setup will increase throttle response and overall power through out the RPM range. This is a bit of an odd ball downpipe, the two resonators will keep the exhaust quiet while increasing tone. Great for a stealth exhaust or commuter car where power is desired without the sound.