The 32SX is a great engine and turns a 10-6 as fast as an FX40. It is lighter and you may have to canopy glue some lead weights to balance. Unless you are flying off a paved runway, I wouldn't go any smaller for an engine. The LT40 is on the heavy side for a trainer and even a 40 has trouble getting it off the ground if the grass hasn't been cut in a while.