Take your ignition performance to the next level with the HKS M40G Super Fire Racing Spark Plug. This high-performance Iridium plug is engineered specifically for heavily tuned JDM engines where reliability under high boost and high RPM is non-negotiable.
The M40G features an NGK Heat Range 8 equivalent, making it the perfect "colder" plug for engines running increased boost levels over factory specifications.
0.6mm Iridium Alloy Center Electrode: Minimizes voltage requirements for a cleaner, stronger spark that improves ignition even in rich fuel environments.
Platinum Ground Electrode: Ensures high durability and consistent performance over a long service life, outperforming standard copper or nickel plugs.
Carbon-Fouling Resistance: Designed with a thermal edge that helps discharge carbon buildup, preventing misfires during street driving or prolonged idling.
Standard Reach Design (G-Type): Optimized for the combustion chamber geometry of classic performance heads, ensuring the spark is delivered exactly where it’s needed.
Part Number: 50003-M40G
Plug Type: G Type (Standard Reach)
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
The HKS M40G is the industry standard upgrade for some of the most iconic engines:
Nissan: Skyline GT-R (RB26DETT), Silvia/180SX (SR20DET), Skyline (RB25DET/RB20DET)
Toyota: Supra/Chaser (1JZ-GTE / 2JZ-GTE), MR2/Celica (3S-GTE)
Mazda: RX-7 (13B-REW / 20B) — Note: Check specific rotary leading/trailing requirements.
Mitsubishi: Evolution I - IX (4G63T)
Subaru: WRX/STI (Early EJ20/EJ25 models with standard reach heads)
Important: These plugs are sold individually. Most customers require a set of 6 (for RB/JZ) or 4 (for SR/4G63). Please update your cart quantity accordingly.
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