I've got the 46AX that's not quite tweaked for reliable runs but it will be soon (still kind of new). One of our more senior members has the 55AX on a Kadet Senior and I flew it last week. A superb engine! The low end on it was perfect and even the high end, which we didn't use much on the Kadet, has such a low note with the new muffler design that it wasn't much louder than a similar sized four stroke.