Abstract: An interference-based exhaust noise attenuation device and method for exhaust flow from an internal combustion engine that generates compressive waves in the exhaust flow. The device includes at least a direct path for the exhaust flow; a looped path for the exhaust flow, with volumes of the direct path and the looped path differing by an amount that results in a staggered rearrangement of the compressive waves in the paths; a splitter that splits the exhaust flow into the direct path and the looped path; and a merger that merges the exhaust flow from the direct path and the looped path. When the exhaust flow from the direct path and the looped path are merged, at least some noise cancellation occurs. In other embodiments, plural direct paths, looped paths, splitters, and/or mergers can be used in various combinations.

Abstract: A drive sprocket for a snowmobile, a drive train using the sprocket, and a method of using the sprocket to drive a track for a snowmobile. The drive sprocket includes a round base, a plurality of convolute lugs on the base, and a plurality of involute lugs on both sides of the base. The base is preferably disk shaped, and the convolute lugs are preferably aligned with the involute lugs. In the preferred embodiment, a number of convolute lugs is one half a number of involute lugs. The convolute lugs should line up with windows in a track for the snowmobile, and the involute lugs should line up with gaps between knobs on the track for the snowmobile. Preferably, the sprocket also includes a hub with a through hole for a drive shaft and stiffening arms radiating from the hub.