Laid a few engines over the plans . A ST .75 , Saito 1.00 and a .56 . My .72 is mounted in a Twist right now , but the foot print is close to the .56 . The plane well probably weigh 8 to 9 lb,s with the mods so a Saito .72 would probaly fly it well , but a .91 would have the reserve to pull thru loops and and floats wont be a problem..