STi + 2.5L turbo owners:
The correct spark plug for you is SOA part number 22401AA630 AKA NGK ILFR6B. A substitute might be LFR6A-11 or LFR6AIX-11 if you want iridium.
Denso Iridium IKH22 is the correct sized one step colder plug.
NGK iridium LFR7AIX, is the correct sized one step colder plug. Or one could use the NGK iridium ILFR7H if you change the gap.
Currently no other manufacturer makes aftermarket spark plugs designed for the STi + 2.5L turbo. Many use aftermarkets anyway.
WRX owners (2002-2005):
Plug Maker/Type/Part Number/Car Type Used/Heat Range
NGK/Copper/BKR6ES/WRX/stock
NGK/Copper/BKR7ES/WRX/one step colder
NGK/Copper/BKR6E/WRX/stock
NGK/Copper/BKR7E/WRX/one step colder
NGK/Platinum/BKR6EGP/WRX/stock
NGK/Platinum/BKR7EGP/WRX/one step colder
NGK/Platinum/PFR6G/WRX/stock <—-OEM plug
NGK/Platinum/PFR7G/WRX/one step colder
NGK/Iridium/BKR6EIX/WRX/stock
NGK/Iridium/BKR7EIX/WRX/one step colder
Denso/Iridium/IK20/WRX/stock
Denso/Iridium/IK22/WRX/one step colder
Champion/Copper/RC10YC4/WRX/stock
Champion/Copper/RC9YC4/WRX/one step colder
Autolite/Copper/3923/WRX/stock
Autolite/Copper/3922/WRX/one step colder
Autolite/Platinum/AP3923/WRX/stock
Autolite/Platinum/AP3922/WRX/one step colder
Autolite/Platinum/APP3923/WRX/stock
Autolite/Platinum/APP3922/WRX/one step colder
Denso Spark Plug Locator
NGK Spark Plug Locator
Autolite Spark Plug Locator
****PFR7B (NGK Part Number 4853) is the correct one step colder plat plug for the 2002-2005 WRX no matter what their website says. The out of the box gap should be at or close to .030. I called the NGK USA toll free # today to find this out and they said they are aware that their site sucks butt and will update it “soon”. Info as of April 2005.****