Here is a project for a GZ .061. This engine turns a 4.2x4 prop about 36,000 on 15% nitro. With higher timing and more nitro it can turn 42,000 with the same prop, but replacing tiny engine parts every other run gets old. The RTF weight of this plane will be less than 12 ozs and I believe there is over 24 ozs of thrust on tap.