Some guys are having trouble with them, but some other guys are having a great time with them. OS were supposed to bring out a new O ring or something, but I don't know if it made a difference. I think though, that if you know how to run in an engine properly, then it'll run goooood. Compared to the YS, here it is in short. The OS has more power, but worse throttle response. I will be putting one in my Widebody 60 in a couple of months time.