I have to agree with Dar about the muffler, it is the reason Tower motors are thought to be strong.

I put the tower muffler on a .46 TT and .46FX both of those motors beat the tower .46 by 500rpm all running identical fuel and props and all tested on the same day.

Nothing wrong with the Tower motors but I almost always have to adjust the mixture each time I'm at the field, the TT and OS are practically set and forget.