NGK Iridium Long Life Spark Plug – ILKR8E6 | Heat Range 8 | Box of 4 | NGK 1422

NGK ILKR8E6 Iridium Long Life spark plugs, sold as a box of 4. Heat range 8, resistor type, laser iridium centre electrode tip, 19mm thread reach. Designed for performance and forced induction applications running higher combustion temperatures. NGK stock number 1422.

Laser Iridium Construction

The ILKR8E6 uses NGK’s laser iridium centre electrode tip — a fine-wire iridium tip laser-welded to the electrode for consistent spark formation and extended service life. Iridium is six times harder and has a significantly higher melting point than platinum, allowing a finer electrode tip diameter (0.6mm) without the wear rate of a platinum or copper plug. The finer tip requires less voltage to initiate the spark, improving ignition reliability particularly under high-boost conditions where cylinder pressure works against spark formation. A platinum pad on the ground electrode provides complementary wear resistance for distributorless ignition systems.

Heat Range 8 — Performance and Forced Induction

NGK’s heat range scale runs from cold (higher number) to hot (lower number). Heat range 8 is on the cooler end of the common performance range — the plug transfers heat away from the tip more rapidly, keeping the electrode tip temperature lower under the higher combustion temperatures generated by forced induction, increased boost, or aggressive ignition timing. Running a plug that’s too hot for the application risks pre-ignition from a glowing electrode tip — heat range 8 provides the thermal margin needed for modified and boosted applications. Confirm the correct heat range for your specific engine tune and boost level with your tuner before selecting plugs.

Specifications Decoded

• ILK — Iridium Long Life series
• R — Resistor (suppresses RF interference with engine electronics)
• 8 — Heat range 8 (cooler)
• E — 19mm thread reach
• 6 — 0.6mm iridium tip electrode diameter

Common Applications

The ILKR8E6 is a commonly specified plug for Subaru EJ-series turbocharged engines (WRX, STI, Forester XT, Legacy GT) and other 4-cylinder forced induction applications requiring heat range 8. Always verify fitment against your specific vehicle’s plug specification or your tuner’s recommendation — heat range selection is application and tune-dependent.

Box of 4. Verify plug fitment, thread reach, and heat range against your vehicle specification and tune before installing. Gap plugs to your ignition system’s specification — do not assume factory gap is correct for your application. Torque to manufacturer’s specification — do not overtorque iridium plugs.

Specifications

• Brand: NGK
• Part Number: ILKR8E6
• NGK Stock Number: 1422
• Series: Iridium Long Life
• Centre Electrode: Laser iridium tip, 0.6mm
• Ground Electrode: Platinum pad
• Heat Range: 8
• Thread Reach: 19mm
• Type: Resistor
• Quantity: Box of 4
• Weight: 0.4 lbs (box)