To maximize SEO for the HKS 50003-M40I, we need to highlight that this is an ISO Type plug. While it shares the same $14\text{mm} \times 19\text{mm}$ dimensions as the M40 and M40G, the "I" (ISO) designation refers to a specific height standard used by many modern and late-model JDM engines.

Here is an SEO-optimized Shopify description for the Australian market:

HKS Super Fire Racing Spark Plug - M40I (50003-M40I)

Elevate your engine's performance with the HKS M40I Super Fire Racing Spark Plug. This ISO Type high-performance plug is engineered for drivers who demand maximum ignition reliability. With a heat range equivalent to NGK #8, the M40I is the perfect upgrade for tuned, turbocharged, or high-compression engines that generate more heat than a standard factory setup can handle.

Designed to prevent pre-ignition and engine knock, the HKS M-Series is a favorite among Australian tuners for its ability to provide a consistent spark even under extreme boost.

Key Performance Features

• ISO Type Design: Specifically manufactured to ISO standards, ensuring perfect fitment for a wide range of modern Japanese performance vehicles.

• 0.6mm Iridium Alloy Center Electrode: Requires lower voltage to ignite, which improves throttle response and ensures a strong spark in harsh combustion environments.

• Platinum Ground Electrode: The square platinum chip significantly increases the life of the plug and maintains a precise spark gap under high-load circuit driving.

• Anti-Vibration Engineering: The shortened outer electrode reduces weight and resists the high-frequency vibrations common in high-RPM performance engines.

• HKS Thermal Edge Technology: The ceramic insulator features a specialized edge that discharges to burn off carbon deposits, preventing misfires after long periods of idling or cold starts.

Technical Specifications

• Part Number: 50003-M40I

• Plug Type: ISO Type (M-i Series)

• Heat Range: NGK #8 Equivalent

• Thread Size: $14\text{mm} \times 19.0\text{mm}$

• Wrench Size: $16\text{mm}$

• Electrode Material: Iridium Center / Platinum Ground

Vehicle Compatibility

The HKS M40I is a highly versatile plug used in many legendary platforms, including:

• Nissan: Silvia S13/S14/S15 (SR20DET), Skyline R33/R34 (RB25DET), Stagea (RB25)

• Toyota: Supra (JZA80), Chaser (JZX100), Altezza (3S-GE), Aristo (2JZ-GTE)

• Honda: S2000 (F20C), Integra Type R (DC2/DC5), Civic Type R (EK9/EP3)

• Mitsubishi: Lancer Evolution (Early models)

Purchasing Information: Plugs are sold individually. For a 6-cylinder engine (Skyline/Supra), please order 6. For a 4-cylinder engine (Silvia/Honda/Evo), please order 4.