809726 Mercruiser PLATE

Illustration 1 g00411724
Air inlet and exhaust system components (1) Aftercooler (2) Air inlet (3) Turbocharger compressor wheel (4) Inlet valves (5) Exhaust valves (6) Turbocharger turbine wheel (7) Exhaust outlet (8) Inlet manifold (9) Exhaust manifoldThe components of the air inlet and exhaust system control the quality of air and the amount of air that is available for combustion. The components of the air inlet and exhaust system are the following components:
Air cleaner
Turbocharger
Aftercooler
Cylinder head
Valves and valve system components
Piston and cylinder
Exhaust manifold Inlet air is pulled through the air cleaner into air inlet (2) by turbocharger compressor wheel (3). The air is compressed and heated to about 150 °C (300 °F) before the air is forced to aftercooler (1). As the air flows through the aftercooler the temperature of the compressed air lowers to about 43 °C (110 °F). Cooling of the inlet air increases combustion efficiency. Increased combustion efficiency helps achieve the following benefits:
Lower fuel consumption
Increased horsepower outputAftercooler (1) is a separate cooler core that is mounted in front of the engine radiator. The engine fan moves ambient air across both cores. This cools the turbocharged inlet air and the engine coolant.From the aftercooler, air is forced into inlet manifold (8). Air flow from the inlet chambers into the cylinders is controlled by inlet valves (4). There are two inlet valves and two exhaust valves (5) for each cylinder. The inlet valves open when the piston moves down on the intake stroke. When the inlet valves open, cooled compressed air from the inlet port is pulled into the cylinder. The inlet valves close and the piston begins to move up on the compression stroke. The air in the cylinder is compressed. When the piston is near the top of the compression stroke, fuel is injected into the cylinder. The fuel mixes with the air and combustion starts. During the power stroke, the combustion force pushes the piston downward. The exhaust valves open and the exhaust gases are pushed through the exhaust port into exhaust manifold (9) as the piston rises on the exhaust stroke. After the exhaust stroke, the exhaust valves close and the cycle starts again. The complete cycle consists of four strokes:
Inlet
Compression
Power
ExhaustExhaust gases from exhaust manifold (9) enter the turbine side of the turbocharger in order to turn turbocharger turbine wheel (6). The turbine wheel is connected to the shaft that drives the compressor wheel. Exhaust gases from the turbocharger pass through exhaust outlet (7), a muffler and an exhaust stack.Turbocharger
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Turbocharger (1) Air inlet (2) Compressor housing (3) Compressor wheel (4) Bearing (5) Oil Inlet port (6) Bearing (7) Turbine housing (8) Turbine wheel (9) Exhaust outlet (10) Oil outlet port (11) Exhaust inletThe turbocharger is installed on the center section of the exhaust manifold. All the exhaust gases from the engine go through the turbocharger. The compressor side of the turbocharger is connected to the aftercooler by pipe.The exhaust gases enter turbine housing (7) through exhaust inlet (11). The exhaust gases then push the blades of turbine wheel (8). The turbine wheel is connected by a shaft to compressor wheel (3) .Clean air from the air cleaners is pulled through compressor housing air inlet (1) by the rotation of compressor wheel (3). The action of the compressor wheel blades causes a compression of the inlet air. This compression gives the engine more power by allowing the engine to burn more air and more fuel during combustion.When the load on the engine increases, more fuel is injected into the cylinders. The combustion of this additional fuel produces more exhaust gases. The additional exhaust gases cause the turbine and the compressor wheels of the turbocharger to turn faster. As the compressor wheel turns faster, more air is forced into the cylinders. The increased flow of air gives the engine more power by allowing the engine to burn the additional fuel with greater efficiency.
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Typical example of a turbocharger with a wastegate (12) Canister (13) Actuating leverSome turbochargers use a wastegate. The wastegate is controlled by boost pressure. At high boost pressures, the wastegate opens. The wastegate closes in order to increase boost pressure. With this arrangement, the turbocharger can be designed to be more effective at lower engine speeds.When the engine is operating under conditions of low boost, a spring pushes on a diaphragm in canister (12). This action moves actuating lever (13) in order to close the valve of the wastegate. Closing the valve of the wastegate allows the turbocharger to operate at maximum performance.As the boost pressure increases against the diaphragm in canister (12), the valve of the wastegate is opened. When the valve of the wastegate is opened, the rpm of the turbocharger is limited by bypassing a portion of the exhaust gases around the turbine wheel of the turbocharger.Note: The turbocharger with a wastegate is preset at the factory and no adjustment can be made.Bearings (4) and (6) for the turbocharger use engine oil under pressure for lubrication. The oil comes in through oil inlet port (5). The oil then goes through passages in the center section in order to lubricate the bearings. Oil from the turbocharger goes out through oil outlet port (10) in the bottom of the center section. The oil then goes back to the engine lubrication system. Valve System Components
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Valve system components (1) Valve bridge (2) Valve rotator (3) Rocker arm (4) Pushrod (5) Valve springs (6) Valves (7) Valve guide (8) Camshaft (9) LifterThe valve system components control the flow of inlet air into the cylinders during engine operation. The valve system components also control the flow of exhaust gases out of the cylinders during engine operation.The crankshaft gear drives the camshaft gear through an idler gear. Camshaft (8) must be timed to the crankshaft in order to get the correct relation between the piston movement and the valve movement.The camshaft has three camshaft lobes for each cylinder. Two lobes operate the inlet and exhaust valves, and one operates the unit injector mechanism. As the camshaft turns,