Integrated axially varying engine mufflers, and associated methods and systems. An arrangement in accordance with one embodiment of the invention includes a tailcone having a tapering external surface, a cavity disposed within the surface, and an engine muffler disposed within the cavity. The engine muffler can have a tapering outer surface, a porous inner surface disposed inwardly from the outer surface, and a plurality of cells disposed between the outer surface and the inner surface in fluid communication with the perforations of the inner surface. The inner surface can be positioned adjacent to an exhaust gas flow path having an entrance aperture and an exit aperture. Cells positioned toward the entrance aperture can have a first dimension extending away from the gas path, and cells positioned toward the exit aperture can have a second, different, dimension extending away from the exhaust gas path. Accordingly, the tapered muffler can be integrated with the tapered tailcone, and can provide sounds attenuation over a range of frequencies.