Abstract: An off-road vehicle includes a frame and an engine. The engine includes a cylinder block and a cylinder head, on which an exhaust passage is arranged. The cylinder head is provided with a supplementary air supply passage for mixing air into the exhaust gas discharged from the combustion chamber. Alternatively, the supplementary air supply passage can be included in the exhaust system, such as in a cylinder head mounting flange of the exhaust pipe, upstream of an oxygen sensor and first and second stage catalytic converters. The exhaust gas from the engine is further oxidized by air, which reduces the content of components such as CO and NOx in the exhaust gas, improving environmental protection.

Abstract: An air intake system includes an air cleaner for housing an air filter element therein above an off road vehicle engine, and a surge tank, which buffers the filtered air, at a location beside the engine. A descending tube from the air cleaner connects into a top cover of the surge tank, and an outlet tube of the air intake system extends horizontally from the top cover of the surge tank for connection into the throttle of the engine. A vapor recovery pipe connect the crankcase of the engine, lower than the outlet tube, back up to the air cleaner upstream of the filter element. The surge tank includes a tank bottom casing removably connected to a tank upper cover, with the descending tube and the outlet tube connecting into the tank upper cover.

Abstract: An air intake system includes an air cleaner for housing an air filter element therein above an off road vehicle engine, and a surge tank, which buffers the filtered air, at a location beside the engine. A descending tube from the air cleaner connects into a top cover of the surge tank, and an outlet tube of the air intake system extends horizontally from the top cover of the surge tank for connection into the throttle of the engine. A vapor recovery pipe connect the crankcase of the engine, lower than the outlet tube, back up to the air cleaner upstream of the filter element. The surge tank includes a tank bottom casing removably connected to a tank upper cover, with the descending tube and the outlet tube connecting into the tank upper cover.