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Decent.
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Prices may varyThis product ranks #14 of 31 in Spark Plug.Three above it ↓
Last reviewed August 13, 2026
TL;DR NGK LFR7AIX is one heat range colder than OEM spec, the community-standard cold plug for Stage 2+ boosted Subaru EJ255/EJ257 builds, with an iridium center electrode (tip diameter not disclosed) and no explicit NGK mileage rating for this application.
Heat range 7 iridium plug for boosted EJ255/EJ257 engines running above stock boost. Iridium center electrode confirmed from the Iridium IX designation; tip diameter not disclosed. M14×1.25 thread, 26.5mm reach, trivalent anti-seize thread coating. Community-confirmed for Stage 2+ EJ builds on NASIOC and r/WRX; some out-of-box gap variation reported; verify gap before installation. Well-reviewed by owners.
Right pick for WRX/STI Stage 2+ tuned builds where the tuner specifies one step colder than OEM; cross-reference community-confirmed across NASIOC, IWSTI, and r/WRX. Skip if running stock boost: OEM heat range 6 is the correct spec, and heat range 7 at stock boost increases fouling risk.
No chemical exposure pathway: passive ignition-system replacement part with no SDS. Iridium electrode mass is small; extended service interval reduces per-vehicle-mile consumption versus copper-tier equivalents. Steel shell is recyclable as ferrous scrap; alumina-ceramic insulator goes to landfill via standard municipal disposal.
The Amazon listing for NGK Iridium IX LFR7AIX Spark Plug (4-Pack) carries a California Prop 65 warning. California requires this warning on a very wide range of manufactured goods — including rubber, vinyl, plastic, and metal automotive parts — whenever trace exposure to any of roughly 900 listed substances (commonly phthalates or heavy metals) is possible, regardless of whether the specific product poses a meaningful health risk. As a passive accessory, NGK Iridium IX LFR7AIX Spark Plug (4-Pack) has no Safety Data Sheet, so there's no chemistry breakdown to translate beyond that.
Marketing copy from NGK, via Amazon. Not editorial.
Per manufacturer cross-reference, not a physical test fit. A single generation often forks by engine, trim, and market.
Check this against your owner's manual before you buy
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