NGK Iridium IX LFR7AIX Spark Plug (4-Pack)
Priced as of May 27, 2026
4.7(458 ratings)Buy on AmazonSaved to your guest loadout. Sign up to also save to your Cabinet (consumables) or Kit (tools you own).
As an Amazon Associate and affiliate partner, CarCareTruth earns from qualifying purchases. Full disclosure
Prices may varyThe Podium · Top 3 in Spark Plug
See the full ranking →This product ranks #6 of 8 in Spark Plug.Three above it ↓
CarCareTruth's Analysis
Last reviewed May 27, 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.
What it is and how it performs
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. 4.7 stars, 458 reviews.
Who should buy this — and who should skip it
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.
Safety and environmental impact
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.
From the manufacturer
Marketing copy from NGK, via Amazon. Not editorial.
- •Trivalent metal plating provides superior anti-corrosion and anti-seizing properties
- •Corrugated ribs prevent flashover
- •Pure alumina silicate ceramic insulator, provides superior strength and better heat transfer
- •Copper core aids in heat removal
Weekly pick
One product, one safety verdict, every week. No spam.
Manufacturer videos
Manufacturer specifications
- Brand
- NGK
- Core Material
- Iridium
- Thread Size
- 14mm x 1.25mm
- Top Material Type
- Ceramic
- Vehicle Service Type
- Car, Truck
- Brand Name
- NGK
- Manufacturer Part Number
- LFR7AIX
- UPC
- 087295023099
- OEM Equivalent Part Number
- FORD%1505812
- Model Number
- 2309
- Unit Count
- 4 Count
- Manufacturer Warranty Description
- Includes manufacturer provided warranty
More from NGK
More in Spark Plug
Denso
SK20HR11 Iridium Long Life Spark Plug
CCT 7.8 · RecommendedHealth 9.5
ACDelco
41-962 Double Platinum Spark Plug
CCT 7.4 · RecommendedHealth 9.5
Denso
PK20TT Platinum TT Spark Plug
CCT 6.6 · DecentHealth 9.5
As an Amazon Associate and affiliate partner, CarCareTruth earns from qualifying purchases. Full disclosure
Community
0 postsShare how you use this product
Drop a quick comment or post a full review with photos and a star rating.
Sign in to postNew here? Create a free account.
Top Amazon review
↗External — Amazon's most-helpful review for context.
I'm happy and my Subaru STi is happy!
The NGK Iridium IX Spark Plug is a standout performer in the world of automotive maintenance.The first thing that strikes you is the build quality. These spark plugs exude durability and precision engineering. The use of iridium in the electrode ensures excellent longevity and consistent performance over the long haul. I've found that they easily outlast conventional copper or platinum plugs, making them a cost-effective choice in the long run.Installation is a breeze, thanks to the well-crafted design. The hexagonal nut at the top of the plug simplifies removal and installation, even in tight engine spaces. I appreciate the ease with which these plugs fit into various vehicle models.When it comes to performance, NGK's Iridium IX Spark Plugs shine. They offer excellent ignition efficiency, resulting in smoother idling, improved fuel efficiency, and reduced emissions. I've noticed a noticeable boost in engine responsiveness and power delivery after switching to these plugs. Whether you have a daily driver or a high-performance vehicle, these spark plugs can make a significant difference.One more noteworthy feature is their ability to resist fouling and carbon buildup. I've experienced fewer misfires and less maintenance hassle since using NGK Iridium IX Spark Plugs.While they might come at a slightly higher price point compared to standard spark plugs, the enhanced performance and extended lifespan make them a worthwhile investment. If you're looking to optimize your engine's performance and reliability, these spark plugs are an excellent choice.In summary, NGK Iridium IX Spark Plugs are a top-notch option for automotive enthusiasts and anyone looking to improve their vehicle's performance and longevity. Their quality, ease of installation, and impressive results make them a standout choice in the spark plug market.Will continue to purchase!