| 摘要 |
PURPOSE:To aim at reconciling the ensuring of satisfactory ignition performance and the enhancing of output power, by merging at first exhaust ports of adjacent engine cylinders which are adjacent with each other in such a condition that the exhaust ports of each engine cylinder are extended substantially radially from the center of the cylinder, thereby to reduce the resistance of exhaust gas. CONSTITUTION:Exhaust passages 17 communicated with exhaust ports 8 of engine cylinders 1a through 1d, which are extended substantially radially from the center of each engine cylinder, are assembled together with exhaust ports 8, 8 of the first and fourth engine cylinders 1a, 1d downstream of a position where the other adjacent exhaust ports 8 of each adjacent engine cylinders are at first merged together. Further in each engine cylinder 1a through 1d, a mounting space may be obtained in an cylinder head 3 between two adjacent exhaust ports 8 and therefore, a spark plug fitting hole 18 communicated with a combustion chamber 6 is formed in this space. Thus, it is possible to reconcile the ensuring of satisfactory ignition performance and the enhancing the output power of the engine due to reduction in the resistance of exhaust gas. |
