NGK 4905 R7438-8 Racing Iridium Fine Wire Spark Plug 14mm Gasket Seat Heat Range

Vehicle Fitment

• Universal racing application - no specific OEM automotive fitment; designed for modified, high-compression, and forced-induction racing engines requiring a 14mm x 1.25mm gasket seat spark plug

Fitment Notes

• Thread: 14mm x 1.25mm - verify engine head thread spec before ordering
• Seat Type: Gasket - engines requiring a tapered/conical seat require a different plug
• Reach: 26.5mm (1.04") - critical to match to engine head depth to avoid piston contact or insufficient combustion chamber exposure
• Plug is pre-gapped at 0.028" (0.7mm) - gap must be adjusted to match the requirements of your specific engine, ignition system, and power level
• Heat Range 8 - a colder heat range plug suited for high-output and forced-induction applications; verify correct heat range for your engine tune
• Sold individually - order quantity to match cylinder count
• Due to extreme racing use conditions, this plug is not covered under NGK's standard warranty

Features

• Fine-wire 1.0mm iridium center electrode delivers superior ignitability, reduced required firing voltage, and exceptional durability under sustained high-RPM racing conditions
• Platinum-tipped ground electrode resists wear and erosion from aggressive fuel mixtures and high-pressure combustion environments
• Special insulator nose configuration optimizes throttle response and improves anti-fouling performance in racing applications
• Corrugated ribs on the insulator prevent electrical flashover in high-voltage ignition systems
• Pure alumina silicate ceramic insulator provides superior dielectric strength and more efficient heat transfer than standard ceramic formulations
• 98% pure copper core maximizes heat dissipation from the electrode to the shell, maintaining the correct operating temperature across a wide heat range
• Triple-seal construction prevents combustion gas leakage around the plug body under extreme cylinder pressures
• Solid terminal type - compatible with most racing ignition wire boots and coil-on-plug adapters designed for solid terminal plugs

Specifications

• NGK Stock Number: 4905
• NGK Part Number: R7438-8
• Series: NGK Racing
• Heat Range: 8 (Colder)
• Thread Diameter: 14mm
• Thread Pitch: 1.25mm
• Seat Type: Gasket
• Reach: 26.5mm (1.04")
• Hex Size: 5/8" (16mm)
• Terminal Type: Solid
• Pre-Set Gap: 0.028" (0.7mm) - adjust for application
• Center Electrode Material: Iridium
• Center Electrode Type: Fine Wire, 1.0mm, Non-Projected
• Ground Electrode Material: Platinum-Tipped
• Insulator: Pure Alumina Silicate Ceramic
• Core: Copper
• Seals: Triple
• Torque (Cast Iron Head): 18-25.3 lb-ft
• Torque (Aluminum Head): 18-21.6 lb-ft
• Sold As: Individually (1 plug per package)

Included Components

• 1x NGK Racing Spark Plug (PN: R7438-8 / Stock: 4905)

Product Description

The NGK 4905 (R7438-8) is a Race Series spark plug featuring a fine-wire 1.0mm iridium center electrode and a platinum-tipped ground electrode, engineered for the demands of modified, high-compression, and forced-induction racing engines. The iridium fine-wire tip reduces the voltage required to fire the plug, improving combustion efficiency and ignitability at high RPM, while the platinum ground electrode resists the accelerated wear common in racing fuel and boost environments. At Heat Range 8, this is a colder-running plug suited for higher-output applications where more heat must be transferred away from the firing tip.

The pure alumina silicate ceramic insulator and corrugated ribs prevent flashover in high-voltage ignition systems, while the copper core and triple-seal construction manage heat dissipation and combustion gas containment under extreme pressure. The 14mm x 1.25mm gasket seat configuration and 26.5mm reach suit a wide range of racing engine heads. Plugs are pre-gapped at 0.028" but must be adjusted for the specific engine, ignition system, and power level. Sold individually - order one per cylinder.