Intake manifold and outboard motor

An intake manifold, suitable for an engine, the intake manifold comprising:

• a surge tank, die-molded to temporarily store intake air;
• and a plurality of branch pipes, in communication with the surge tank, wherein the surge tank comprises, on an outer wall of the surge tank, a flange part and a reinforcement rib, a sensor unit configured to detect a state quantity of the intake air being installed to the flange part, the flange part comprises:
• a fitting hole, having a predetermined axis as a center so as to be fit with a detection part of the sensor unit;
• and two boss parts arranged on a first line and formed to be point-symmetric with the axis as a center, the first line is perpendicular to the axis, the reinforcement rib comprises:
• a parallel reinforcement rib extending in parallel with the first line in a vicinity of the flange part;
• and a limitation piece interfering with a portion of the sensor unit to limit assembling at a time when the sensor unit is assembled erroneously for being deviated from a normal orientation, wherein the limitation piece is formed on the parallel reinforcement rib and has a curved outer profile in a convex shape.