ys engines are competition engines. they provide the power of a much larger engine while weighing less. however, they are heavier than non-supercharged 4 strokes of their same displacement so if you just want a good 91 or 120 to cruise around with, than the ys is definatly not the best choice for you. that is where OS and Saito shine. meanshile if you want a good engine for a 9-10 lbs 3d plane or a warbird or pattern plane, the ys engines are ideal for your application. considering you are using a 4* 60, get the os or saito. they are both exceptional 4 strokes. OS makes a pumped version of their surpass II in both the 91 size and 1.20 size. those are great motors as well. the only reason i sold mine was becuase i wanted a ys for my new plane (a 3d plane) and so far it has been just an exceptional engine, but it not the best engine for a 4* 60.