HI LEE! I did a little research for you. The 46 engines give you more for the money VS the 40s. The 40s main place anymore is rulebook events where that is the size limit. If you can get a 46 for the same price and weight as a 40, then you are getting a good deal. I have a TT PRO 40, and 46. They put out tons of power, but they vibrate, and they are heavy. The TT46 weighs almost a pound, It costs $75. They tend to shake the muffler halves apart if run in the 17K range alot. The EVOLUTION 46 is $90 and it is only rated up to 12K RPM. It weighs 13 oz. The OS LA is $65. It weighs 11 oz which is lighter than many 40s. It's got 1.2HP compared to the TT46 1.4 HP and it's rating is taken at a realistic 15K instead of 16K RPM for the TT. I think the weak point about the LA 46 is the plastic backplate. I run the LA 40 [same engine basically] in combat and they have survived numerous crashes without any damage, we don't even have time to clean them out, just change the prop and restart.