Cobra PowrFlo Slip-On Mufflers For Harley Touring The PowrPro slip-on mufflers begin with a 4-1/2 slim-line tip at the far end and smoothly tapers to its 4 front. There are various perks to consider when acquiring such system such as the ease of installation, amazing sound, and the PowrFlo mufflers are just difficult to beat. Features: 4-1/2 inch body tapers to 4 round at the front 4-1/2 machined aluminum, thin-line tip 3 core for superior performance Acoustical engineering developments allow an incredibly deep sound because of intense, class-leading resonance absorption and prevention Uses proprietary materials with specific acoustical dampening and thermal insulation properties The frequency and location of the perforation patterns in the cores creates significant sound scattering in the mid frequencies, which helps to enhance the low frequency tones