Lean 540, get the 2.1, you won't be sorry! The 1.8 will fly the airplane and you will be able to do the basic aerobatic sequence but you won't have the muscle to pull sustained vertical. I have the Patty with a 2.1 and it is a fantastic combination, possibly the best flying aircraft I have ever owned! I am running the Menz S 20x10 prop, 5% Powermaster Castor/Synthetic blend and an OS 'F' type plug. The 2.1 Moki is the best large glow engine on the planet IMHO! Good Luck!

jmw[8D]