HKS 50003-M40iL Super Fire Racing Iridium Spark Plug Long Reach ISO HR8 14mm

Vehicle Fitment

• Universal Fit - Compatible with any vehicle requiring a 14mm x 26.5mm long-reach ISO-type spark plug with Heat Range 8 (NGK equivalent) / Heat Range 24 (Denso equivalent)

Fitment Notes

• This is a universal spark plug sold individually - confirm your engine requires a 14mm x 26.5mm long-reach ISO-type thread before ordering
• The "L" suffix denotes Long Reach (26.5mm thread length); do not substitute for the standard-reach 50003-M40i (19mm thread) even though both share ISO-type and Heat Range 8
• Heat Range 8 (NGK) / Heat Range 24 (Denso) - one step colder than the M35iL (HR7); suited for moderately to heavily tuned forced induction or high-compression naturally aspirated engines
• For short-reach ISO Heat Range 8 applications (19mm thread), see 50003-M40i; for long-reach ISO Heat Range 7, see 50003-M35iL

Features

• 0.6mm Iridium Alloy Center Electrode reduces voltage requirement and delivers consistent, high-energy spark initiation under advanced tuning conditions
• Outer electrode incorporates a square platinum chip that improves wear resistance and boosts ignition efficiency when paired with the iridium center
• Short-type anti-vibration outer electrode is mass-reduced and shape-optimized to resist high-RPM vibration for extended service life
• Tapered outer electrode tip design maintains optimal combustion chamber space volume for improved flame kernel development
• Thermal Edge ceramic insulator actively discharges to reduce carbon deposits after prolonged idling or variable combustion conditions
• Spark Support Gap between the insulator tip and outer electrode base prevents carbon bridging and maintains reliable ignition under high load
• High iridium melting point of 2,454°C tolerates elevated compression and minor detonation without electrode degradation
• Nickel-coated housing resists corrosion and prevents premature housing deterioration

Specifications

• Part Number: 50003-M40iL
• Series: Super Fire Racing M-Series
• Type: Long Reach ISO
• Heat Range: 40 (HKS) / NGK #8 equivalent / Denso #24 equivalent
• Center Electrode: 0.6mm Iridium Alloy
• Outer Electrode: Platinum Square Chip
• Thread Size: 14mm x 26.5mm
• Wrench Size: 16mm
• Sold: Individually (per piece)

Included Components

• 1x HKS Super Fire Racing M40iL Iridium Spark Plug (Long Reach ISO Type)

Product Description

The HKS Super Fire Racing M40iL (50003-M40iL) is the long-reach ISO-type variant of the M40i, engineered for engines with deeper cylinder head thread depths requiring a 14mm x 26.5mm plug. It delivers identical electrode technology and Heat Range 8 (NGK equivalent) performance as the standard M40i, but is specifically built for long-reach applications where the 19mm standard plug would not seat correctly. This makes it the correct choice for moderately to heavily tuned ISO-thread engines with long-reach cylinder head specifications.

Combining a 0.6mm iridium alloy center electrode with a platinum-tipped outer electrode, the M40iL ensures lower ignition voltage requirements, sharper spark delivery, and improved combustion efficiency versus OEM plugs. The Thermal Edge insulator and Spark Support Gap work together to prevent carbon fouling under both high-load and extended idle conditions, while the shortened anti-vibration outer electrode sustains durability at elevated RPM. Plugs are sold individually - verify long-reach ISO thread compatibility and order the correct quantity to match your cylinder count.