I was recently looking for an engine for a SIG Senior. The specs called for anywhere from a .45 to a .53. I wanted a .60 or higher. For some reason hobby retailers advertise their planes using and under powered engine. I found out the hard way. Anyway, I saw an OS 60 LA a believe it was for $109.00. I thought that was cheap. When talking to my fellow club members they told me that the LA is advertised as a .60 but has the power of a .45. That explained the price. I paid an extra $50.00 dollars and bought the OS .61 FX. Don't get me wrong. I love OS engines, you just have to be careful with the LA models.