all the above mentioned 2-strokes would be awesome in the GeeBee!! I have a saito 182 twin in mine, it's fairly fast but also quite heavy. This plane needs to be on as much of a diet as possible unless you like landing fast! The robart struts help with the typical bouncing problems this palne can show, but they also add a decent amount of weight. I think the ultimate power/weight/sound would be a YS140, but too much cabbage for me.