Exhaust manifold for internal combustion engine

Abstract

An exhaust manifold provides improved output by suppressing exhaust interference between cylinders at the exhaust manifold. An air-fuel ratio sensor is installed in position where it can uniformly detect the exhaust gas of each cylinder. The exhaust manifold has a plurality of exhaust tubes, one per cylinder, that connect with a collector case. Each of exhaust tubes has a linear portion located directly above the section where it merges with the collector case. The exhaust tubes are connected to the collector case such that the center axes of the linear portions intersect at intersection point inside the collector case or downstream thereof. The air-fuel ratio sensor is arranged such that its detecting part is positioned in the vicinity of the intersection point. Depending upon whether the exhaust tubes of cylinders have firing orders that are successive or not determines whether the exhaust tubes are slanted or parallel with respect to each other.