91741M Mercury MAIN JET

Turbocharged
Illustration 1 g01163268
Turbocharged (1) Cylinder head (2) Air inlet (3) Turbocharger (4) Exhaust outlet (5) Inlet manifold (6) Exhaust manifold (7) Exhaust valve (8) Number 1 cylinder (9) Inlet valve
Illustration 2 g01163281
Turbocharged aftercooled (1) Cylinder head (2) Air inlet (3) Turbocharger (4) Exhaust outlet (5) Inlet manifold (6) Exhaust manifold (7) Exhaust valve (8) Number 1 cylinder (9) Inlet valve (10) Raw/sea water aftercooler (11) Sea water inlet to aftercooler (12) Sea water outlet from aftercoolerTurbocharged engines pull outside air through an air cleaner into air inlet (2) of turbocharger (3). The suction is caused by the turbocharger compressor wheel, which is used to compress the air. The air then flows through aftercooler (10) (if equipped). The aftercooler utilized sea water in order to cool the inlet air. Cooling of the inlet air causes the air to become more dense. This increases combustion efficiency and this increases horsepower output. The air flows from the aftercooler (if equipped) into inlet manifold (5) which directs an even distribution of the air to each engine cylinder. Air is pulled into the engine cylinder through inlet valve (9) during the intake stroke of the piston. Then, the air is mixed with fuel from the fuel injection nozzles. After the fuel combustion occurs, the exhaust gases flow out of the cylinder through exhaust valve (7). The exhaust gases then flow through exhaust manifold (6) and into the turbine side of turbocharger (3). The hot exhaust gases are used to drive the turbine inside the turbocharger. The turbine is used in order to drive the compressor wheel. The exhaust gases then exit the turbocharger through exhaust outlet (4) .Each piston makes four strokes:
Intake
Compression
Power
ExhaustThe sequence of the strokes by all of pistons in all of the engine cylinders provide constant air flow to the inlet system during the engine operation.Naturally Aspirated
Illustration 3 g01163293
Naturally aspirated (1) Cylinder head (2) Air inlet (4) Exhaust outlet (5) Inlet manifold (6) Exhaust manifold (7) Exhaust valve (8) Number 1 cylinder (9) Inlet valveEngines which are naturally aspirated pull outside air through an air cleaner directly into inlet manifold (5). The air flows from the inlet manifold to the engine cylinders. The fuel is mixed with the air in the engine cylinders. After the fuel combustion occurs in the engine cylinder, the exhaust gases flow through the exhaust manifold (6). The exhaust gases then exit through exhaust outlet (4) .Each piston makes four strokes:
Intake
Compression
Power
ExhaustThe sequence of the strokes by all of pistons in all of the engine cylinders provide constant air flow to the inlet system during the engine operation.Turbocharger (If Equipped)
A turbocharger increases the temperature and the density of the air that is sent to the engine cylinder. This condition causes a lower temperature of ignition to develop earlier in the compression stroke. The compression stroke is also timed in a more accurate way with the fuel injection. Surplus air lowers the temperature of combustion. This surplus air also provides internal cooling. A turbocharger improves the following aspects of engine performance:
Power output is increased.
Fuel efficiency is increased.
Engine torque is increased.
Emissions of the engine are improved.
Illustration 4 g00302786
Components of a turbocharger (typical example) (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 inletA turbocharger is installed between the exhaust and intake manifolds. The turbocharger is driven by exhaust gases which flow through the exhaust inlet (11). The energy of the exhaust gas turns the turbine wheel (8). Then, the exhaust gas flows out of the turbine housing (7) through the exhaust outlet (9) .The turbine wheel and the compressor wheel (3) are installed on the same shaft. Therefore, the turbine wheel and the compressor wheel rotate at the same rpm. The compressor wheel is enclosed by the compressor housing (2). The compressor wheel compresses the inlet air (1). The inlet air flows into the engine cylinders through the inlet valves of the cylinders.The oil from the main gallery of the cylinder block flows through the oil inlet port (5) in order to lubricate the turbocharger bearings (4) and (6). The pressurized oil passes through the bearing housing of the turbocharger. The oil is returned through the oil outlet port (10) to the oil pan.Some turbochargers have a wastegate. The wastegate is controlled by the boost pressure. This allows some of the exhaust to bypass the turbocharger at higher engine speeds. The wastegate is a type of flapper valve that automatically opens at a preset level of boost pressure in order to allow exhaust gas to flow around the turbine. The wastegate allows the design of the turbocharger to be more effective at lower engine speeds.The wastegate is controlled by a diaphragm. One side of this diaphragm is open to the atmosphere. The other side of this diaphragm is open to the manifold pressure. An air/fuel ratio control is installed between the turbocharger and the fuel injection pump. The air/fuel ratio control performs the following functions:
The fuel is limited on acceleration in order to prevent an overspeed condition.
The generation of black smoke is reduced.
The fuel efficiency is improved and emissions are reduced at low boost when the fuel rack is limited for low power output.The air/fuel ratio control is a nonserviceable part. Adjustment and repairs should only be done by a Caterpillar Dealer.Cylinder Head And Valves
The valves and the valve mechanism control the flow of the air and the exhaust gases in the cylinder during engine operation. The cylinder head assembly has two valves for each cylinder. Each valve has one valve spring. The ports for the inlet valves are on the left side of the cylinder head. The ports for the exhaust valves are on the right side of the cylinder head. Steel valve seat inserts are installed in the cylinder head for both the inlet and the exhaust valves. The valve seat inserts can be replaced.The valves move along valve guides. The valve guides can be replaced. The exhaust valve