Description

Genuine NGK ZFR6FIX-11 (Part No. 3668) Iridium IX Spark Plug Specifications, Features & Applications

The NGK ZFR6FIX-11 (Part No. 3668) is a high-performance spark plug from NGK’s Iridium IX series, engineered for enhanced ignitability, long life, and superior combustion performance. With an ultra-fine iridium center electrode and a tapered ground electrode, this plug delivers reliable spark energy, improved throttle response, smooth idle, and fuel-efficient combustion — all while meeting strict OEM quality standards. It’s widely used in many Honda and other vehicles requiring a 14 mm iridium ignition solution.

Specifications:

Brand: NGK
Part Number: 3668
Manufacturer Model: ZFR6FIX-11
Type: Iridium IX
Center Electrode Core Material: Copper core
Center Electrode Tip Material: Iridium fine-wire
Ground Electrode Material: Nickel alloy, tapered cut
Electrode Gap: 1.1 mm (~0.044″) (factory pre-set)
Thread Diameter: 14 mm
Thread Pitch: 1.25 mm
Thread Reach: 19 mm (3/4″)
Hex Size: 16 mm (5/8″)
Heat Range: 6 (NGK heat scale)
Resistor: Yes (≈5 kΩ)
Seat Type: Flat / Gasket type
Terminal Type: Non-removable nut solid terminal

Key Features:

Ultra-Fine Iridium Center Electrode

An extremely fine iridium tip (~0.6 mm) allows for quick, clean ignition with reduced voltage requirements, improving engine start-up and throttle response. This fine electrode also helps maintain spark consistency over long life.

Tapered Ground Electrode Design

The specially shaped ground electrode promotes efficient flame propagation across the gap, contributing to smoother idling, quicker acceleration, and reduced misfire tendencies compared to standard plugs.

Iridium Durability & Longevity

Iridium has a higher melting point and wear resistance than platinum or nickel, significantly extending service life — often outperforming conventional plugs by miles and hours of engine operation.

Resistor Built-In for Stable Performance

The internal resistor (~5 kΩ) suppresses electrical noise and interference with onboard electronics, delivering smoother ignition and protecting sensitive sensors.

Corrosion & Seize Protection

Trivalent plating on threads helps guard against corrosion and makes installation and removal easier — reducing the risk of thread galling.

Applications — Compatible Car Engines

The NGK ZFR6FIX-11 (3668) Iridium IX spark plug is widely used in many Honda vehicles and other engines that specify a 14 mm spark plug, 19 mm reach, 1.1 mm gap, and a heat range 6 iridium plug. As an OEM-level replacement or upgrade, it is engineered for reliable operation in naturally aspirated, fuel-injected engines where responsive performance and long service intervals are desired.

Common Vehicles & Engines (Examples):

Honda Cars

• Honda CR-V 2.0L (R20A) — various years

• Honda Civic 1.3L (L13A)

• Honda Civic 1.5L (D15Z)

• Honda Civic 1.6L (D16Y)

• Honda Civic 1.8L (R18A / R18Z)

• Honda Civic 2.0L (K20Z)
  (These are typical fitments where NGK ZFR6FIX-11 is listed)

Other Possible Fitments
Some aftermarket references show ZFR6FIX-11 used in European and other models — including certain BMW, Chevrolet, and Dodge/Jeep engines — when matching thread size, reach, gap, and heat range requirements. Always confirm exact fitment via manufacturer specs or a fitment lookup tool.

Performance Benefits:

🔹 Sharper Ignition & Faster Acceleration – Reduced firing energy needed yields a more responsive engine.
🔹 Improved Cold Starts & Idle Stability – Fine-wire iridium improves combustibility at low RPM and during warm-up.
🔹 Longer Service Life – Iridium resists wear better than platinum or copper, meaning fewer replacements over time.
🔹 Better Fuel Efficiency – More complete combustion may slightly enhance MPG and reduce unburned fuel.
🔹 Reduced Emissions & Smoother Operation – Stable combustion lowers misfires and contributes to smoother power delivery.

Summary — Why Choose NGK ZFR6FIX-11?

The NGK ZFR6FIX-11 (3668) Iridium IX spark plug is designed for drivers seeking consistent OEM-quality performance with enhanced durability and efficiency. Its fine iridium electrode and optimized design deliver reliable ignition, smoother engine running, and a longer service life compared to standard copper plugs — making it a strong choice for Honda vehicles and many other compatible engines.