Subaru cylinder heads are identified by an alphanumeric code cast into the side of every head. The code features a letter and two numbers. WRX and STI EJ25 cylinder heads have four letter codes (B, V, W, D) identifying the year and type of vehicle. The codes will appear as B25, V25, W25 and D25.
- D25 - Single AVCS, 2006-14 WRX
- B25 - Single AVCS, 2004-2006 STI
- V25 - Single AVCS with Air Pump, 2007 STI
- W25 - Dual AVCS, 2008-18 STI
, subaru STI