1674 DIESEL TRUCK ENGINE Air Induction And Exhaust Systems Caterpillar

Air Induction And Exhaust Systems

This engine has an exhaust driven turbocharger to provide compacted air to the cylinders.

The exhaust gases enter the turbine housing and are directed through the blades of a turbine wheel, causing the turbine wheel and a compressor wheel to rotate.

Filtered inlet air from the air cleaner is drawn through the air inlet of the compressor housing by the rotating compressor wheel. The air is forced through the aftercooler to the inlet manifold of the engine and is compressed by action of the compressor impeller.

When the intake air passes through and is compressed by the turbocharger, it becomes heated and becomes less dense. By directing air through the aftercooler located between the turbocharger and the inlet manifold, some of that heat is removed from the air. The aftercooler is a simple device resembling a small radiator core. Coolant from the engine passes through the core tubes and the compressed air is directed around the tubes. Since the temperature of the coolant is lower than the air, the air is cooled as it leaves the aftercooler. This means more air (oxygen) is available for combustion, resulting in more fuel being burned and more power produced.

When engine load increases, more fuel is injected into the engine cylinders. The increased volume of exhaust gas causes the turbocharger turbine wheel and compressor impeller to rotate faster. The higher RPM of the impeller increases the quantity of inlet air. As the turbocharger provides additional inlet air, more fuel can be burned; hence more horsepower derived from the engine.

The turbocharger is mounted to the engine exhaust manifold. All the exhaust gases from the diesel engine pass through the turbocharger.

The turbocharger bearings are pressure-lubricated by engine oil. The oil enters the top of the center section and is directed through passages to lubricate the thrust bearing, sleeves and the journal bearings of the turbocharger. Oil leaves the turbocharger through a port in the bottom of the center section and is returned to the engine sump.


Maximum turbocharger speed is determined by the rack setting, the high idle speed setting and the altitude at which the engine is operated. The high idle speed and the rack setting are not the same for all altitudes.


If the high idle speed or the rack setting is greater than specified for the altitude at which the engine is operated, damage to engine or turbocharger parts can result.

The fuel pump rack has been set by qualified personnel for a particular engine application. The governor housing and turbocharger are sealed to prevent unqualified personnel from tampering with the adjustments.

The engine can be operated at a lower altitude than specified without danger of engine damage. In this situation the engine will perform at slightly less than maximum efficiency. When operated at a higher altitude, the rack setting and high idle speed setting must be changed.

The principal cause of fouled valves, damaged bearings, worn piston rings and cylinder liners is the entrance of airborne foreign matter into the engine cylinders; therefore, it is necessary to incorporate a precision built dry-type or oil bath air cleaner in the system. The intake ducts should be so arranged as to be most convenient to service, but located away from areas of dust and exhaust concentration. The importance of cleaning or filtering the air entering the engine cannot be over-emphasized.

AVSpare recommends the use of an air cleaner service indicator for dry type air cleaners. The service indicator senses pressure drop across the air cleaner and a red indicator will remain visible when service is necessary. The service indicator will prevent unnecessary filter changes and reduce maintenance costs while ensuring proper engine operation.