Briggs & Stratton 498984S Super Lo-Tone Muffler For 8 and 11 HP Horizontal Engines and 18 HP Opposed Twin Horizontal Engines Briggs & Stratton 498984S Super Lo-Tone muffler Fits 8 and 11 HP horizontal engines Fits 18 HP opposed twin horizontal engines and selected models OHV Twins (horizontal and vertical c/s models/remote mount) Special RAF reduced noise design.