Hey flyboy11, I thought the same thing when I first looked but then I started thinking about and it didn't make sense that that was the case. First of all, the TT pro series is pretty much a replica of the SF series and very close to the FX series. If what your saying is true than that means that the TT engine without muffler weighs over 2.5oz's more than the 46fx without muffler. That doesn't seem quite right. Especially since the TT engine doesn't have a remote needle valve to add more weight like the FX has. Secondly, all of the other specs for the other engines on the ACE site seem to say the weight of the engine w/muffler. For example, the GP 42 says something like 12.6 which I know is the wight w/muffler. And the Pro 36 says something like 11.8 (I can't remember the exact number) and I know that that is the weight w/muffler. So you can see why I would question the Tower Specs for the Pro 46. I know that 15.8oz's seems a little light for that engine with the muffler, but I think that it also seems too heavy to be the weight without the muffler. Hope this makes sense.