HKS Super Fire Racing Spark Plug M-Series - XL Type, Heat Range NGK #8

HKS Super Fire Racing Spark Plug M-Series - XL Type, Heat Range NGK #8

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HKS Super Fire Racing Spark Plug M-Series - XL Type Heat Range #8

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Spark Plug Type Thread Size Wrench Size Heat Range Product Code No.
XL Type φ12×26.5mm 16mm NGK #8 SUPER FIRE RACING M40XL 50003-M40XL




Ultimate spark plug "M".

Ignition ability, durability, anti-insulation are all reinforced. HKS has made the best plug for both tuning engines and stock engines.


  • 0.6mm Iridium Alloy Centre Electrode
    Iridium alloy centre electrode reduces voltage requirement and improves ignition performance and durability.
  • Outer Electrode with Platinum Chip
    The outer electrode incorporates a square platinum chip which improves durability, and combining with the iridium centre electrode boosts ignition performance.
    The outer electrode features a shortened tip design and tapered shape while maintaining the necessary space for proper ignition.
  • Short Type Outer Electrode (Anti-Vibration)
    The outer electrode has been shortened and engineered with the ideal shape to decrease weight for resistance against vibration. This anti-vibration design improves longevity of the outer electrode.
  • Thermal Edge
    After long idling or under various combustion conditions, carbon build up can occur causing misfires. The thermal edge of the ceramic insulator discharges to help decrease carbon deposits.
  • Spark Support Gap
    Discharge occurs in the spark support gap (space between the tip of insulator and the base of the outer electrode) to help prevent carbon build up.

Performance and Efficiency

  • Increased Ignition Performance
    Decreased voltage requirement strengthens ignition performance under harsh conditions like lean mixture or high boost pressure.
  • Improved Durability
    New material and design improve durability which allows for use under hard combustion conditions like continuous high load during circuit driving or aggressive tuning.
    * Improper combustion condition and wrong heat range selection may cause damage to the spark plug.
  • Decreased Carbon Deposits
    Thermal edge and spark support gap help prevent carbon build up for better ignition under various combustion conditions.

Special Design RE-type for Rotary Engines

Rotary engines reciprocating design have a different mechanism and combustion condition. RE-type spark plugs are specially designed to meet the different requirement for rotary engines. The straight shape platinum outer electrode enables reliable ignition performance.

Heat Range Conversion Chart

HKS 25 30 35 40 45 50 52.5 55
DENSO社 16 20 22 24 27 31 32 34
NGK社 5 6 7 8 9 10 10.5 11

* Above information is the reference for heat resistance.