This powerful YS .91 Helicopter engine has been optimized to provide the ultimate power with maximum efficiency and reliability. The YS .91 includes a larger bore cylinder design for superior operation thus reducing cut outs improved carburetor design for ease of adjustment factory preset fuel regulator and best of all it is the same physical size as the 80ST making it easy to install. This engine is so powerful we recommend using a gear ratio of 1-7.5 to 1-8.0. Instructions included in kit.
