I have a TH .40 size Trainer that I bought used for my son. This had an OS .40fp (not all that different than the la). Yes it flew the plane, but always at full throttle and not enough power that I would want for pulling a student out of trouble. I also have a LT 40 that I had an "OLD" OS Max .40 (Ball bearing engine) on it and had plenty of power. For the "Cost" of an OS la series engine you can by a quality Ball Bearing engine with around 30% more power. There is no way I would put an OS la 40 or 46 in a Tiger 2 or Advanced 40. Also, the la and fp series engines use "air bleed" type carbs, while most others use 2 needle type.