Honda Grom/Monkey Big Bore Kit

KOSO Honda Grom / Monkey 170cc Big Bore Kit

Unleash maximum performance from your Honda GROM or Monkey with the KOSO 170cc Big Bore Kit. Engineered for riders seeking a significant power upgrade, this precision kit delivers improved throttle response, higher top-end speed, and a more aggressive character on the street or track.

• Ceramic-coated aluminum cylinder for superior heat management and reduced wear
• 61mm bore paired with a forged piston and premium ring kit
• 11.5:1 compression ratio — requires high-octane fuel for safe, optimized performance
• Complete top-end gasket kit and necessary banjo bolts included for installation

Compatibility: Designed specifically for Honda GROM and Monkey models. Professional installation recommended to ensure correct jetting, timing, and tuning.

Note: Not legal for use in California on pollution-controlled vehicles. Race use only in California — waiver available.