I don't know, but I have to agree with Apia (Tom) & smosher9. I have two GMS 47's, one I have on a trainer, and it runs fine, right from my test stand running to on the plane. I do usually open up a new motor searching for metal flakes, tightening screws. And the the other looks just as good. Mine didn't need any "surgery", just a little tinkering with the tune, but mine hauls just fine. Hey,,, go ahead, buy the overpriced OS. I still like using good sound tuning techniques to get all my motors to run correctly. But then again, I like the TT GP42. I'm sure I'd like OS as well.