The NGK Iridium IX CR9EHIX-9 is the absolute best premium spark plug upgrade for high-revving inline-four motorcycles like the Honda CB400 Super Four, CBR250RR, and Hornet series. Engineered by NGK Spark Plugs, this performance plug replaces standard nickel or copper plugs (like the traditional CR9EH-9) to deliver superior throttle response, steadier idling, and up to double the service lifespan

• Better Throttle Response: The fine-wire tip concentrates the spark, ensuring faster flame expansion and crisper throttle action.
• Anti-Fouling Design: Built-in thermo-edge slots around the center electrode burn off carbon deposits automatically to prevent misfires.
• Anti-Corrosion Shield: Plated with a trivalent metal chromate coating to protect the shell from seizing up inside aluminum cylinder heads