The first Rascal that I built had an OLD worn out OS 40 four stroke in it that flew the plane NICE. It would do consecutive loops without loosing much altitude till you got sick...Inside AND Outside! The wing loading on this plane is very nice. I'd recommend trying out the 40 LA. I've been using one with a 11x4 APC on my funfly for awhile with great results. I think you will be pleased. OH by the way also be sure to use a OS #8 plug it'll smooth out the transition on the LA since the low end is pretty much always rich and non adjustable.