The TT site lists weights with muffler, the OS site lists weights without muffler. Look at the differance in weight of the OS FX .46 and Pro .46. The Pro .46 is actually a tad lighter, but the muffler may weigh a tad more, same with the Pro .46. The TT .91 is not as heavy as it would seem when you find that the OS site is weight without muffler. But a 91 4 stroke muffler is probably less than 2 ounces in weight.