I've been flying my Avistar since mast spring. It started out with a .40 ABC schneural ported 2-stroke which flew it quite well. I eventually got hooked on 4-strokes and stuck a Magnum .52 from ebay for about $120. The weight difference was only about 1 ounce and actually didn't need any extra weight in the tail to balance it. The acceleration is much better and the climb is awesome! People at the feild say they've never seen a 4-stroke on a trainer. Then they say they've never seen trainer that flies like that. So the 4-stroke is well worth it the slightly extra weight and money.