HKS Super Fire Racing M35i Iridium Spark Plug – MX-5 MK1 / MK2 / MK2.5 • 50003-M35-I

HKS Super Fire Racing M35i Iridium Spark Plug – 50003-M35-I

Performance iridium ignition spark plug for Mazda MX-5 MK1 / NA, MK2 / NB and MK2.5 / NB-FL 1.6L and 1.8L petrol engines (1989–2005) using the compatible ISO-type 14mm spark plug arrangement and an NGK-equivalent heat range of 7.

The HKS Super Fire Racing M35i has been developed to deliver reliable ignition performance in demanding engine applications, combining a fine iridium-alloy centre electrode with a platinum-tipped ground electrode.

Spark plugs play an essential role in the combustion process, igniting the compressed air and fuel mixture inside each cylinder. A consistent spark helps maintain efficient combustion, smooth running and dependable engine response.

The M35i uses a 0.6mm iridium-alloy centre electrode designed to improve ignition performance while offering excellent resistance to electrode wear. The platinum-tipped ground electrode supports durability and consistent ignition characteristics.

Additional HKS design features include a short anti-vibration ground electrode, thermal edge and spark support gap, developed to help maintain ignition performance and reduce the risk of carbon fouling under demanding operating conditions.

With an NGK-equivalent heat range of 7, this is a colder-range performance spark plug than many standard factory applications. It is particularly relevant to appropriately tuned, high-load or forced-induction engines where the engine specification calls for this heat range.

Product features and specifications:

• Product type: Performance iridium spark plug
• Manufacturer: HKS
• Product series: Super Fire Racing M35i
• Manufacturer part number: 50003-M35-I
• Spark plug configuration: ISO type
• Heat range: HKS M35 / NGK equivalent 7
• Centre electrode: Iridium alloy
• Centre electrode diameter: 0.6mm
• Ground electrode: Platinum-tipped
• Thread diameter: 14mm
• Thread pitch: 1.25mm
• Thread reach: 19mm
• Hex / socket size: 16mm
• Engine applications: Compatible Mazda B6 1.6L and BP 1.8L petrol engines
• Vehicle applications: Mazda MX-5 MK1 / NA, MK2 / NB and MK2.5 / NB-FL
• Spark plugs required per engine: 4

HKS Super Fire Racing Technology:

• 0.6mm iridium-alloy centre electrode: Fine electrode design to promote reliable ignition with excellent durability.
• Platinum-tipped ground electrode: Supports electrode durability and consistent spark performance.
• Short ground electrode: Designed to improve resistance to vibration.
• Thermal edge: Helps manage deposits and support anti-fouling performance.
• Spark support gap: Additional design feature intended to support ignition under demanding conditions.

Heat Range Selection: The M35i is equivalent to NGK heat range 7 and is colder than many standard spark plugs used in naturally aspirated MX-5 engines. It should be selected to suit the engine's operating conditions, modifications and ignition requirements. A colder spark plug is not automatically an upgrade for every standard road engine.

Common replacement reasons: Spark plug replacement may be required following electrode wear, carbon fouling, inconsistent ignition, misfires or during scheduled ignition-system maintenance. Performance engine builds may also require a different spark plug heat range to suit increased combustion temperatures and engine loads.

Fitment advice: Designed for engines using a compatible 14mm thread, 19mm reach and ISO-type spark plug terminal arrangement. The M35i must be matched to the engine's required heat range and ignition-system configuration. A four-cylinder Mazda MX-5 engine requires four matching spark plugs.

Other items to consider: Ignition leads, ignition coils, engine oil, oil filter, air filter, appropriate spark plug removal and installation tools, and other ignition-system service components.

Useful tools / consumables: 16mm spark plug socket, suitable extension bar, calibrated torque wrench, plug gap measuring tool and compressed air or suitable cleaning equipment for the spark plug wells.

Difficulty guide: DIY Difficulty: Easy to Moderate. Spark plug replacement is a routine service operation on most MX-5 MK1 and MK2 engines. Correct plug selection, careful installation and the manufacturer's tightening procedure are important to avoid cylinder head thread damage.

Why HKS? HKS is a well-established Japanese performance engineering specialist producing engine, ignition, induction and forced-induction components for road and motorsport applications. Its Super Fire Racing spark plug range is designed to support reliable ignition performance in engines operating under demanding conditions.

Installation / service notes: Allow the engine to cool before removing the existing spark plugs. Clean around the spark plug wells to prevent debris entering the cylinders. Inspect the replacement plugs and confirm the correct specification before installation. Start threading each spark plug by hand to avoid cross-threading, then tighten using the appropriate HKS or engine manufacturer's procedure. Reconnect the ignition system securely and confirm normal engine operation following replacement.