get the 60 size for your 120 it should have enough power. if it makes a difference. i have used these engines on a 60 size u can do. os 91 fx, satio 150 ,satio 180 ,and os 160 fx. all worked fine i like the satio 150 best. tho the 160 fx was fun. i thought i never would say a plane was overpowerd but it was a little. pull out of hover at 3 clicks off idle.[sm=bananahead.gif] the 46 flys good. but the same rules work on them. to bigger flys better.