Hi, welcome to bhq. This Banshee thing is pretty new to you? What is your setup right now? Having a more powerful engine mean that you need good supporting parts all around the engine. Serval cub is an engine more trail oriented, with a smoother power delivery than a drag engine. A stock banshee is 350cc, 64mm bore x 55mm stroke A 421cc is a 68mm bore x 58 stroke (+4mm) . 4mill mean +4mm sroke on the crank. Ask questions and read stuff here before commiting to buy. Where are you from? Envoyé de mon SM-G935W8 en utilisant Tapatalk