The Avistar is fairly light and will fly like a trainer just fine with a 40 engine. With a higher performance 46 such as the OS 46AX the plane will fly fast like a sport plane at full throttle. My opinion on the best brands for these engine sizes are either the Thunder Tiger or the OS. Both are easy to adjust and run reliably. With the OS though stick with the FX or AX series. The LA are reliable but very weak running. All ways look at the next plane and see if the engine will work in that as well. For the price difference I would look at 46 size engines. The weight is pretty much the same but you get more power. What happened to the engine from the Sky Raider?? [8D]