I had the 66 inch extra and flew it with several different engines on it. I tried the magnun 91 4 stroke first and it flew the plane great. You will not have ulimimted vertical with it but it will haul the plane straight up pretty good. I then tried a Saito 100 and it had more power but it didn't really fly the plane any better. I then tried a Thunder Tiger 91 and this was the engine I liked the best. It will turn the same size prop at the same RPM as the Saito 100. It runs alot smoother than the saito too. All of the saito engines that I own all
vibrate alot at idle. The magnum and TT are both smoother running engines. The only draw back to the TT engine is that it weighs about 3 oz more than the saito. If you compare quality they are about the same IMO. The TT engine is built really beefy and has a large cylinder and head. That is where the extra weight comes from. I have never had any trouble from it either. It always starts and runs very good. I have about 300 flights on it now and have only had to adjust the valves once. The price is also quite a bit less than the saito. The TT engine is also built much nicer than the Magnum. Try one I bet you will be very happy with it. I like all of my 4 stroke engines but bang for the buck I would buy another Thunder Tiger.

Rick