You know, I have forgotten what was inside. I have vague memories of it being more like a Mousse Can type of muffler. The idea being to cool the exhaust gasses down before the gasses exit, which results in the small exhaust outlet as the exhaust gasses have cooled down some by the time the reach the outlet. The inner tube is smaller in diameter than the outer tube.

The two mufflers seem to be about the same for noise output, but that is mainly because of the propeller making most of the noise then at the higher RPMs. You can get the tuned pipe howl like propeller noise using both mufflers on the engines. One of these days I need to get a DB meter so I can check noise levels of things better.