This header is covered by California Air Resources Board EO # D-276-12 for 2001-2003 WRX. Please Note that even though this header will fit models from 2001-2018 the EO # only covers 2001-2003 WRX. Increased performance through efficient flow?Greater durability through high quality, T-304 stainless steel, material and a unique, stiffened, flex joint. LEGAL ONLY FOR RACING VEHICLES THAT MAY NEVER BE USED, OR REGISTERED, OR LICENSED FOR USE, UPON A HIGHWAY.