Look at House of Balsa web site for smaller planes. I think the little engine I had was a .48?? I used it in a small space walker. Been a while. What John mentioned about the older four strokes is really true, compared to what we have today they were pretty anemic. Todays top four strokes are about the same as there two stroke counter parts, not in rpm but torque, they can really pull around a plane. YS is in a class all by itself but I won't get into that. I still use my OS four strokes too.