Turbocharger: Description and Operation

Fig. 18 Turbocharger:

Fig. 19 Turbocharger air flow:

Fig. 20 Intercooler assembly. Mustang SVO:

The turbocharger, Figs. 18 through 20, is an exhaust driven device which compresses the air-fuel mixture that is used to increase engine power on a demand basis, allowing a smaller, more economical engine to be used. A turbine in the exhaust gas flow is connected through a shaft to the impeller (compressor). During normal, steady operation, the turbine does not rotate with sufficient speed to boost pressure to compress the air-fuel mixture. As the speed increases, the mixture is compressed, allowing the denser mixture to enter the combustion chambers and develop more engine power during the combustion cycle. The intake manifold pressure (boost) is controlled by a wastegate valve which is used to bypass a portion of the exhaust gasses around the turbine at a predetermined point in the cycle, limiting the boost pressure. A green light on the instrument panel indicates that the turbocharger is in a safe boost condition. A red light and buzzer are used to indicate a malfunction or if boost pressure exceeds a predetermined level. Some models are equipped with a charge air cooler (intercooler) mounted between the turbocharger and throttle body assemblies. The intercooler cools the air flowing out of the turbocharger. The Mustang SVO also uses a turbo boost control system which along with the intercooler, allows higher turbo boost pressures, increased combustion efficiency, engine horsepower and torque. The turbocharger boost control system used on some models, is designed to provide electronic variable boost control. The boost control system provides regulation of the wastegate actuator signal allowing up to 14 psi of turbo boost pressure. The system includes a control module, solenoid/hose assembly, calibrated T-fitting and a relay/switch assembly. Turbochargers are lubricated from the engine oil system. These turbochargers operate at speeds up to 120,000 RPM which makes the lubrication of the bearings which support the shaft important for cooling as well as friction. The oil enters the turbocharger through an inlet fitting in the center housing. This inlet fitting directs oil to the center housing bearings, the oil then drains from the turbocharger through a return hole in the center housing. When changing oil and filter on a turbocharged engine disconnect the ignition switch connector from the distributor then crank engine several times until the oil light goes out. Reconnect the ignition wire to the distributor. This procedure will aid in the filling of the oil system before starting engine.