2-stroke versus 4-stroke, they both have their advantages and disadvantages. 2-strokes are simpler in design and cheaper to buy. 4-strokes characteristically have more torque, especially at lower rpms, swing a bigger prop more easily, have that cool sound, and seem to be more fuel efficient. Both have great throttle response if adjusted and propped properly, but the 4-strokes seem to have an edge here. The Saito 100 is very light, and I think any .91 size 2-stroke will be about the same weight so this isn't an issue. One drawback to the 4-stroke is you may occasionally have to adjust the valves, but it only takes a few minutes to do. I personally would rather have a Saito 100 on the UCD3D if I could afford it. If you look at all the posts here this engine is definitely the most popular choice for this plane. Dozens and dozens of people can't be wrong. If you want to do a lot of hovering around then I think the 4-stroke is the best choice. I think 2-strokes are great engines as are the 4-strokes, but the Saito 100 would be hard to beat on the UCD. The Saito 100 is a very popular engine, so the resale value would probably be very good if you ever wanted to sell it. The Saito has a 3 year warranty, pretty nice since it's longer than most. This is my opinion, and I'm sticking to it! Sorry for the rambling on.

Wade