Stick with the Thunder Tiger. Very good engines. The quality of the Evolution engines is a mixed bag. SOme run great out of hte box. Some run crappy and get worse with every run. I was unfortunate to get one of the bad ones in 61 size. Supposed to be rated for 12000 with an 12-6 APC prop. I could barely get over 11K on the first run and was losing rpms with every flight. I pulled it and replaced with a Tower Hobbies 75 which has run great. My Evo engine now just sits on one of the benches somewhere. [8D]