Outboard marine propulsion devices and exhaust systems for outboard marine propulsion devices

1. An outboard marine propulsion device comprising:

an internal combustion engine having a cylinder head and a cylinder block; and

an exhaust manifold that discharges exhaust gases from the internal combustion engine towards a vertically extending catalyst housing;

wherein the exhaust manifold has a plurality of horizontally extending inlet runners that receive the exhaust gases from the internal combustion engine, and a vertically extending collecting passage that conveys the exhaust gases from the plurality of horizontally extending inlet runners to a bend that redirects the exhaust gases downwardly towards the catalyst housing;

wherein the bend comprises a curved radially outer wall; and

wherein an uppermost inlet runner in the plurality of horizontally extending inlet runners has an uppermost radially inner wall that horizontally extends from an uppermost cylinder in the cylinder head to an uppermost location on the curved radially outer wall so that the exhaust gases flow only horizontally through the collecting passage and then downwardly in the bend;

wherein the uppermost radially inner wall is horizontally aligned with the uppermost location on the curved radially outer wall such that exhaust gases that flow horizontally through the uppermost inlet runner tend to straighten exhaust gases that flow in a swirling flow from the remaining inlet runners in the plurality of inlet runners.

2. The device according to claim 1 , wherein the exhaust manifold does not vertically extend above the cylinder head and cylinder block.