<span style="font-size: larger;"><span style="font-family: Comic Sans MS;">I think for relaxed flying the TT91 4C is nice, its a good engine. But if you want to invest in a nice engine then look at the Saito 100 for this baby. I did help a friend run in the new OS 110 ... oh man ... that baby is sooooooo sweet! Nice exhaust tone and the mechanical sound is not rough. That OS really made me think of going back to 4C engines.</span></span>