2026-10-08 · 5 min read
Subaru WRX STI Spark Plug Replacement Malaysia
The EJ257 turbocharged boxer engine requires iridium spark plugs — NGK BKR7EIX or equivalent. Replace every 30,000 km for a turbocharged application; extending this interval risks misfires and fouling under boost. The EJ257 has four horizontally-opposed cylinders, each requiring one plug. Correct heat range is critical — using a cooler plug helps under boost but requires proper selection.
Subaru WRX STI Spark Plugs
- STI EJ257 spark plugs: iridium; replace every 50,000–60,000 km; EJ257 high compression (8.0:1) and turbo boost creates extreme conditions; plugs more critical on EJ257 than FA20DIT
- STI plug spec: NGK Iridium or Denso Iridium for stock STI; for tuned STI with higher boost — NGK R7437-8 or equivalent one step colder; consult tune builder before changing heat range
- STI knock sensitivity: wrong plug heat range in EJ257 causes knock and pre-ignition — destroys pistons fast; EJ257 is known to be knock-sensitive; always use correct spec plugs
- STI plug torque: 18–22 Nm; never overtighten — EJ257 aluminium head threads strip if overtightened; use anti-seize if reusing plug holes that have been opened multiple times