Developed specifically for the Mini Z, XCR120, Z120 and Yamaha SRX 120 these kits will increase both acceleration and speed without sacrificing any of their abilities to go through deep snow. When testing and developing these kits, we use our stalker ats system to ensure that our results are both accurate and honest. Stock spped is about 8MPH, this kit can boost speed up to 12-15 MPH depending on rider and snow conditions. These kits are easy to install (under 1 hour) and include a gear, hub, chain and governor rod/spring (MINI Z and XC120 also include quick change foot kit). ISR legal. Uses #40 chain. For Arctic, Ski-Doo & Yamaha models, we also recommend a billet chain adjuster,(Part# 430-215) this helps eliminate unnecessary wear, reduces friction and allows kit to perform to its potential.