DENSO Iridium Spark Plug - IU31A 5367

A worn-out spark plug is one of the easiest performance killers in any engine—and one of the cheapest fixes. DENSO Iridium plugs deliver superior ignition consistency and longevity compared to conventional copper plugs, meaning better throttle response, cleaner combustion, and fewer misfires across your entire RPM range. If you're serious about reliability and repeatability, whether on the track or the street, these are the plugs your engine deserves.

The iridium electrode is six times harder than platinum, allowing DENSO engineers to shrink the electrode down to just 0.4mm—a precision that reduces voltage requirements while actually improving firing performance. That's not a trade-off; it's an engineering advantage. The 360° laser-welded electrode seal resists degradation even in extreme heat and combustion stress, while the tapered ground electrode with U-groove design creates an optimal flame kernel area for faster, more complete combustion.

• Iridium electrodes
• 0.4mm electrode diameter
• Heat rating: 4,000°F capable
• 360° laser welding
• Tapered ground electrode
• U-groove design
• Lower voltage requirement
• Extended service life
• OEM-equivalent performance
• MPN: IU31A 5367