for the Funtana - S 40 you need atleast the 70 /4 stroke but even better an 80 sized 4 stoke. forget the 2 stoke engines in these 3D profile jobs. i have an OS 81 in my Funtana 40 and its a pefect combo for any 3D or normal aerobatic flying. so forget the 70 size go for the 80 size 4 strokes then you will be happy.