Best Spark Plugs for Subaru WRX and STI: Performance Boxer Engines

The Subaru WRX and STI are performance icons with turbocharged boxer engines that demand quality spark plugs. Getting the wrong plug in a high-boost engine can cause detonation and serious damage.

WRX FA20DIT (2015+)

The FA20 direct-injection turbocharged engine in the 2015+ WRX uses NGK SILZKBR8D8S Laser Iridium plugs as OEM spec. Pre-gapped at 0.028" to handle the boost pressure. Do not gap wider than OEM spec on a boosted application.

STI EJ257 (Classic)

The legendary EJ257 2.5L turbo boxer is found in STIs through 2021. NGK Iridium TR6IX plugs are popular for the EJ25 at stock boost. For higher boost (Stage 2+), consult your tuner — a colder heat range is often required.

Modified WRX/STI Considerations

If you're running an E85 tune, upgraded turbo, or any significant modification, plug selection becomes critical. Your tuner should specify the correct heat range and gap. Never assume stock plug specs apply to a modified engine.

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