My brother has one and he's tried the Moki2.10, OS1.60, and now finally the Moki 1.80. With the Moki 2.10 it wouldn't waterfall and it would tip stall on landing if too slow (over wingloaded), on the OS it would waterfall super tight but didn't have quite the long straight uplines for IMAC. The Moki 1.80 is the perfect engine for this airframe in our experience. It will Waterfall real tight, flat inverted spin, land at a crawl, and he can take it off, pull to a vertical upline, and you can watch in amazement as it will accelerate upward out of site. It is absolutely awesome. His prop is a Mejlick 19*8 Carbon Fiber. We are about 7-800 feet above sea level I believe.