Just a few of my projects with Ryobi power my Sig 4 star 120 a few mods not to many. Also my three 16% Bi=planes enlarged from Sig plans Hog Bipe I cut and scratch built. The flag Bipe was my prototype and I did later invert the engine from the pic shown to help make it more stable in flight. All fly just great with the stock ryobi the 4* does use an electronic ignition with little power gain.
See 4* flight video here.
http://www.youtube.com/watch?v=XPthz2wrfyU