Koso 150Cc Big Bore Kit Honda Grom / Monkey Enhance your Grom's performance with the 150Cc Big Bore Kit from Koso. This kit will increase your engine's displacement by 17 and raise the compression ratio to 11.38:1 from 10:1. This upgrade results in a substantial boost in power, particularly when combined with a Koso Camshaft and high-quality fuel, making your ride more fun than ever! Features: Cylinder displacement: 150 cc Cylinder material: Aluminum / Black powder coated Piston size: 54 mm Piston type: Forged Compression ratio: 11.38:1 Kit includes: piston ring, piston, pin, gasket kit and cylinder