0437375 JOHNSON DECAL SET, 25SI models

Illustration 1 g00904874
Air inlet and exhaust system
(1) Exhaust manifold
(2) Air inlet heater
(3) Aftercooler core
(4) Exhaust valve
(5) Inlet valve
(6) Air inlet
(7) Exhaust outlet
(8) Compressor side of turbocharger
(9) Turbine side of turbochargerThe 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 manifoldAir is drawn in through the air cleaner into air inlet (6) by turbocharger compressor wheel (8). The air is compressed and heated to about 150 °C (300 °F) before the air is forced to the aftercooler (3). As the air flows through the aftercooler the temperature of the compressed air lowers to about 50 °C (120 °F). Cooling of the inlet air increases combustion efficiency. Increased combustion efficiency helps achieve the following benefits:
Lower fuel consumption
Increased horsepower output
Reduced particulate emissionFrom the aftercooler, air is forced into the inlet manifold. Air flow from the inlet chambers into the cylinders is controlled by inlet valves (5). There is one inlet valve and one exhaust valve 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 complete cycle consists of four strokes:
Inlet
Compression
Power
ExhaustExhaust gases from exhaust manifold (1) enter the turbine side of the turbocharger in order to turn turbocharger turbine wheel (9). 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.The air inlet heater aids in engine start-up and reducing white smoke during engine start-up.Turbocharger
Illustration 2 g00904915
Turbocharger
(1) Compressor wheel housing
(2) Oil inlet port
(3) Bearing
(4) Turbine wheel housing
(5) Turbine wheel
(6) Air inlet
(7) Exhaust outlet
(8) Compressor wheel
(9) Bearing
(10) Oil outlet port
(11) Exhaust inletThe turbocharger is installed on the center section or on the top of the exhaust manifold. All the exhaust gases from the engine go through the turbocharger. The exhaust gases enter turbine housing (4) through exhaust inlet (11). The exhaust gases then push the blades of turbine wheel (5). The turbine wheel is connected by a shaft to compressor wheel (8).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.
Illustration 3 g00907531
Turbocharger with the wastegate
(12) Canister
(13) Line (boost pressure)
(14) Actuating leverThe turbocharger has a wastegate. The wastegate helps improve the emissions of the engine. The operation of the wastegate is controlled by the boost pressure. At high boost pressures, the wastegate opens in order to decrease boost pressure. At low boost pressure, the wastegate closes in order to increase boost pressure.When the engine is operating under conditions of low boost, a spring pushes on a diaphragm in canister (12). This action moves actuating lever (14) 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 through line (13) 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. The exhaust gases are routed through the wastegate which bypasses the turbine wheel of the turbocharger.Bearings (3) and (9) for the turbocharger use engine oil under pressure for lubrication and cooling. The oil comes in through oil inlet port (2). The oil then goes through passages in the center section in order to lubricate the bearings. This oil also cools the bearings. Oil from the turbocharger passes through oil outlet port (10) in the bottom of the center section. The oil then returns to the engine oil pan.Valve System Components
Illustration 4 g00907525
Rocker shaft and rockers
The 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. The camshaft must be timed to the crankshaft in order to get the correct relation between the piston movement and the valve movement.
Illustration 5 g00904080
Valve system components
(1) Rocker
(2) Spring
(3) Pushrod
(4) Valve
(5) LifterThe camshaft has two camshaft lobes for each cylinder. The lobes operate the inlet and exhaust valves. As the camshaft turns, lobes on the camshaft cause lifter (5) to move pushrod (3) up and down. Upward movement of the pushrod against rocker arm (1) results in downward movement (opening) of valve (4).Each cylinder has one inlet valve and one exhaust valve. The valve spring (2) closes the valve when the lifter moves down.Air Inlet Heater
Illustration 6 g00849290
Location of the air inlet heater
(1) Air inlet heater
(2) Fuel lineThe engine is equipped with an air inlet heater (1). The air inlet heater is installed in the inlet manifold in order to heat the intake air in cold weather.
Illustration 7 g00642969
Air inlet heater
(3) Electrical connection