First to fourth exhaust passages are provided in a raw blank of a cylinder block, which can be used for both a first exhaust route and a second exhaust route, one of which is selected for use as an exhaust passage. In the first exhaust route, a fifth exhaust passage couples between opening ends of the first and second exhaust passages and is formed in a separate member from the cylinder block, exhaust gas is allowed to flow via the fourth, first, fifth, second, and third exhaust passages, and a catalyst is placed in the exhaust passages. In the second exhaust route, a communication hole is provided in a partition wall between the fourth exhaust passage and the second exhaust passage while the opening ends of the first and second exhaust passages are closed, and the exhaust gas is allowed to flow via the fourth, second, and third exhaust passages.

An outboard motor has a powerhead that causes rotation of a driveshaft, a steering housing located below the powerhead, wherein the driveshaft extends from the powerhead into the steering housing; and a lower gearcase located below the steering housing and supporting a propeller shaft that is coupled to the driveshaft so that rotation of the driveshaft causes rotation of the propeller shaft. The lower gearcase is steerable about a steering axis with respect to the steering housing and powerhead.

An air intake and exhaust system for a marine engine having an intake manifold and an exhaust manifold includes an air compressor configured to compress ambient air into compressed air and a catalytic converter assembly configured to convert pollutants in an exhaust gas stream received from the exhaust manifold. The air compressor is configured to be fluidly coupled to the intake manifold of the engine for directing at least a first portion of the compressed air to the intake manifold of the engine. The air compressor is also selectively fluidly coupled to the catalytic converter assembly for selectively directing a second portion of the compressed air into the exhaust gas stream at a secondary air injection location at or upstream of the catalytic converter assembly.

An outboard includes a plurality of first branched pipes connected to a plurality of first exhaust ports and a plurality of second branched pipes connected to a plurality of second exhaust ports, respectively, wherein the plurality of first branched pipes are connected to a first collecting pipe and the plurality of second branched pipes are connected to a second collecting pipe. A connector connects the first collecting pipe and the second collecting pipe. The plurality of first branched pipes extend in a direction away from the connector in a plan view, and each includes a first exhaust pathway located farther away from the connector than the first collecting pipe is in the plan view. The plurality of second branched pipes extend in a direction away from the connector in a plan view, and each includes a second exhaust pathway located farther away from the connector than the second collecting pipe is in the plan view.

A heat shield includes an outer jacket including a fluid inlet port and a fluid outlet port, and an inner jacket nested within the outer jacket and spaced apart therefrom to define a fluid passageway therebetween. The fluid passageway is in fluid communication with the fluid inlet port and the fluid outlet port for directing a cooling fluid from the fluid inlet port to the fluid outlet port through the fluid passageway. The inner jacket at least partially defines a main cavity configured to at least partially protect a turbocharger of the marine engine.

A marine drive has a primary exhaust outlet on its lower gearcase that discharges a primary flow of exhaust gas from the engine to seawater in which the marine drive is situated. A secondary exhaust outlet is located on the marine drive above the primary exhaust outlet and discharges a secondary flow of exhaust gas from the engine to atmosphere around the marine drive at least when the engine is operated at an idle speed. A tertiary exhaust outlet is located on the marine drive between the primary and secondary exhaust outlets, and discharges a tertiary flow of exhaust gas from the engine to the seawater or to the atmosphere depending upon a current location of the tertiary exhaust outlet with respect to the seawater. A muffler is configured to reduce noise emanating from the tertiary exhaust outlet.

A heat shield includes an outer jacket including a fluid inlet port and a fluid outlet port, and an inner jacket nested within the outer jacket and spaced apart therefrom to define a fluid passageway therebetween. The fluid passageway is in fluid communication with the fluid inlet port and the fluid outlet port for directing a cooling fluid from the fluid inlet port to the fluid outlet port through the fluid passageway. The inner jacket at least partially defines a main cavity configured to at least partially protect a turbocharger of the marine engine.

An exhaust system for a marine outboard engine including an engine having an engine exhaust port. The exhaust system includes a first exhaust port, a second exhaust port vertically higher than the first exhaust port, a first passage for fluidly connecting to the engine exhaust port and fluidly connected to the first exhaust port, a second passage fluidly connected between the first passage and the second exhaust port, a catalytic converter defining at least in part the second passage, a valve operable to at least partially close the first passage to respectively reduce and increase flow of exhaust gas to the first exhaust port and the second exhaust port, a valve actuator operatively connected to the valve, and a controller operatively connected to the valve actuator for controlling a position of the valve based at least in part on a speed and a throttle request of the engine.

First to fourth exhaust passages are provided in a raw blank of a cylinder block, which can be used for both a first exhaust route and a second exhaust route, one of which is selected for use as an exhaust passage. In the first exhaust route, a fifth exhaust passage couples between opening ends of the first and second exhaust passages and is formed in a separate member from the cylinder block, exhaust gas is allowed to flow via the fourth, first, fifth, second, and third exhaust passages, and a catalyst is placed in the exhaust passages. In the second exhaust route, a communication hole is provided in a partition wall between the fourth exhaust passage and the second exhaust passage while the opening ends of the first and second exhaust passages are closed, and the exhaust gas is allowed to flow via the fourth, second, and third exhaust passages.

An outboard motor has a powerhead that causes rotation of a driveshaft, a steering housing located below the powerhead, wherein the driveshaft extends from the powerhead into the steering housing; and a lower gearcase located below the steering housing and supporting a propeller shaft that is coupled to the driveshaft so that rotation of the driveshaft causes rotation of the propeller shaft. The lower gearcase is steerable about a steering axis with respect to the steering housing and powerhead.