🔧 Overview: NGK LKAR8BHX (Ruthenium HX, OEM 91784)
🚗 Use / Vehicle models
The LKAR8BHX was developed as a replacement for numerous factory inserts such as 22401-JF01D and 22401-JK01D. It is used in vehicles including some Nissan R35 GT-Rs. .
⚙️ Technical data
- Thread: 12 mm × 1.25 mm, with flat gasket seat
- Screw-in depth (reach): 26.5 mm (1.04 in)
- Hexagon: 14 mm (9/16 in)
- Gap size (factory setting): 0.8 mm (0.032 in)
- Resistance: Integrated 5 kΩ resistor for noise suppression
- Heat range: NGK Heat Range 8 – designed for powerful, turbocharged engines with high combustion temperatures
💡 Functional features & benefits
- Center electrode: Fine wire electrode made of ruthenium (≈ 0.4 mm)
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Ground electrode: Platinum fine wire (≈ 0.8 mm), in PSPE design (“Projected Square Platinum Electrode”) for optimized ignition discharge
→ Maximum ignition reliability, long service life and slow electrode wear - Insulator & Core: Pure alumina-silicate ceramic for heat protection, plus a copper core for efficient heat dissipation
- Metal plating: Trivalent finishing protects against corrosion and seizure
- Design feature: Corrugated ribs on the insulator prevent flashover across the ceramic housing
🏎️ Performance profile & service life
- Developed for maximum ignition efficiency, even with lean or rich air-fuel mixtures
- Leads to faster response, smoother idle and better cold start characteristics
- Compared to standard spark plugs, significantly longer replacement intervals: up to 60,000–120,000 miles (≈ 100,000–200,000 km) possible
🛠️ Installation instructions & torque
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Torque when screwing in:
- Cast iron head: approx. 10.8–18 lb-ft (≈ 15–25 Nm)
- Aluminum head: approx. 10.8-14.5 lb-ft (≈ 15-20 Nm)
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Installation tips:
- Clean threads, if necessary apply some copper paste to the threads (except on the sealing bed).
- Screw in the spark plug hand-tight, then tighten with a torque wrench.
- Check tightening after 1000 km (when used in aluminum head).
✅ Conclusion
The NGK LKAR8BHX (Ruthenium HX, 91784) is a modern high-performance spark plug with:
- Excellent ignition energy with extremely thin electrodes
- Very long service life
- Optimized for current turbo engines with high combustion temperatures
Ideal for ambitious drivers who want more efficiency, durability and reliability – especially in newer vehicles and with sporty tuning.