RE: ultra thrust mufflers
The ultra-thrust and jett-stream mufflers are very similar. These are both tuned exhaust systems, and include porting and internal geometry that basically make them a 1/4 wave tuned pipe. Part of the design consideration is the gas velocity and backpressure - which is why these mufflers have carefully sized exhaust outlets, and great consideration is given to the muffler/tank pressure fitting location. Most importantly, they are assembled as a one-piece unit, and neither of them is going to come apart.
Both the Jett-Stream and Ultra-thrust mufflers are available for different rpm ranges (different applications) and of course various sizes and types of engines. As example, the standard Jett-Stream .46 size muffler will boost a TT40, 46 or OS 46FX by and easy 1300-1700 rpm on a 10x6 prop. Target range for this muffler is 14,500 up to 17,500 - with the best boost in power noted over 16,000 rpm. Jett also offers a similar muffler, tuned for about 1000 rpm lower for slightly bigger props, and the SS or LX muffler tuned for 1500 rpm higher for smaller props. (from my test notes, the OS46FX ran between 14,100 and 14,300 with a 10x6 and stock setup - with the jett-stream it ran from 15,800 to 16,000)
The tower muffler is similar in external appearance, but does not have the same internal design consideration or gas flow path. However, it does has demonstrated an 'inadvertant' tuning effect none the less, and aside from the through bolt it is a fairly well designed muffler. Boost of around 800 rpm is common. A bit more on smaller props. The tuning effect for this tends to be right around 15,500 rpm - and can boost up to around 16,000. So if you use this muffler for the Tower 46, or other engines, and prop for something 15K or higher, the muffler does kick in and can give you a few hundered rpm boost (as opposed to a shell and baffle type muffler).
Bob