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For me and others, the Saito .100 is the engine of choice. An APC 16x4 prop is what most like for good pull out from hover. There's another UCD at the field with an OS .91 2-stroke. It doesn't hover as good. Throttle response is different - not as smooth as the 4-strokes. Check out the UCD 60 thread in this forum. It's long but worth the reading.