OH YEAh I mentioned to the guy at the hobby store that someone told me that the O.S...90 would over heat if I decided to put it in the plane, and the reason for that is they don't make a exhaust for the .90 so you have to use the muffler from the .61 which in turn makes it overheat. He also told me I HAD to get an O.S. because super tigre went out of business and i would never find one. ( Tower seems to think different).I dunno i'm new to this whole thing