Wrap-Up

Ready for Review

• A forced induction engine forces in the greatest amount of air into the cylinders.
• The air density changes based on the altitude of operation.
• The volumetric efficiency is affected by the increased pressure of the supercharger/turbocharger.
• A supercharger uses a belt to operate off of the engine crankshaft.
• Superchargers give instant power as they are continuously driven.
• Superchargers can drag on the engine as they are directly driven off of the engine’s crankshaft.
• There are three kinds of superchargers: the Roots type, the centrifugal type, and the twin-screw type.
• A Roots-type supercharger operates within a narrow power band and then does not make more power.
• The centrifugal type also has a preset power band, but it is larger than the Roots type.
• The twin-screw type makes power in the biggest power band but is costlier than others.
• Superchargers are bypass valve (BPV) controlled to maintain the correct amount of boost.
• Centrifugal superchargers are more easily positioned on the engine.
• Roots-type and twin-screw-type superchargers sit on top of the engine and require hood clearance to fit.
• Turbochargers are exhaust gas driven, which compresses the intake air before it gets in the intake.
• Turbochargers use an intercooler to help with lowering the temperature of the compressed air from the turbocharger.
• Turbochargers use engine oil and engine coolant to lubricate and cool the turbocharger.
• There are air-cooled turbochargers that have only an oil pressure feed to the turbocharger.
• Using water/methanol injection helps to cool the cylinders to help prevent detonation.
• Boost control is done with a waste gate, PCM-controlled solenoids, and a blow-off valve (BOV).
• BOVs are operated when the throttle is suddenly closed and excessive pressure has built up in the intake tract.
• Waste gates redirect exhaust gas from the exhaust turbine wheel out the tailpipe to control the speed of the turbocharger.
• When diagnosing a turbocharger failure, the entire engine must be inspected so that the next turbocharger will not fail.
• Blue smoke on a turbocharged engine is a sign that the turbocharger may be allowing oil into the combustion chamber.
• Testing for boost leaks should be conducted whenever there is a power concern.
• A failed exhaust gas recirculation (EGR) system can cause a variable geometry turbocharger (VGT) to become stuck in a certain condition.
• High-quality motor oil should be used and the turbocharged vehicle should be operated within the proper parameters; otherwise, failures can occur.

Key Terms

center housing rotating assembly (CHRA) An assembly that consists of the turbine shaft, impeller, compressor wheels, and bearings that they rotate on.

forced induction The pressurization of airflow going into the cylinder through the use of a turbocharger or supercharger.

supercharger A component that uses external power to turn the compressor wheel to compress the air as it enters the intake system. The supercharger is usually driven by a belt off the crankshaft or directly from an electric motor.

turbocharger A forced induction device driven by exhaust gas pressure and used to compress intake air so that more air can be pushed into the cylinders, creating more power.

variable geometry turbocharger (VGT) A type of turbocharger that is adjustable by directing exhaust gases toward or away from the exhaust impeller. This is a common way to control the turbocharger more precisely in order to match the requirements of the engine.

variable nozzle turbocharger (VNT) A type of turbocharger that uses nozzles to adjust the exhaust gases toward different areas of the exhaust impeller to increase power—usually two exhaust passages.

variable turbine geometry (VTG) Another name used by certain manufactures for the VGT.

Review Questions

1. The turbocharger is operated by what type of power source?
   • Serpentine belt.
   • Electric motor.
   • Exhaust gases leaving the engine.
   • Mechanical drive.
2. All of the following statements with respect to forced induction are true except:
   • A supercharger can increase the power of an engine by increasing the air in the engine.
   • The engine must have different components to maintain engine integrity.
   • A turbocharger must have a separate belt to operate the turbocharger.
   • A supercharger must be monitored with a boost sensor to determine whether the supercharger is producing too much boost.
3. A blow-off valve (BOV) is used on a forced induction engine for what purpose?
   • To bleed off pressure when the throttle is abruptly closed.
   • To control the turbocharger output.
   • To control the supercharger output.
   • To adjust the amount of air entering the intake tract.
4. Choose the correct statement.
   • Superchargers are powered by exhaust gases to make increased pressure in the intake.
   • Turbocharger BOVs are used to determine whether the air is correct for consumption.
   • The charge air cooler (CAC) helps to cool the compressed air to promote more efficient combustion.
   • A supercharger can create increased pressure within the cylinder, which decreases the efficiency of the engine.
5. The forced induction engine may use more oil than a conventional engine because of the increased crankcase pressure.
   • True.
   • False.
6. Overspeeding the turbocharger can cause what part of the turbocharger to fail?
   • The impeller wheel.
   • The turbine shaft bearing.
   • The compressor wheel.
   • The turbocharger housing.
7. Foreign object intrusion into a turbocharger or supercharger can __________.
   • destroy a compressor blade or rotor.
   • increase the pressure output of the system.
   • do nothing; it will simply pass right through the system.
   • be stopped by the mesh screen so that it doesn’t enter any moving parts.
8. Waste gates allow the turbocharger system ____________.
   • to slow down the turbocharger to control an overboost condition
   • to increase the speed of turbocharger
   • and its PCM to change the engine’s mechanical operation
   • to stop operation
9. The mechanical components of a forced induction engine must be able to _______________.
   • operate as a normal engine, with minimal changes
   • handle the increased pressure built up in the cylinder
   • change with the changing needs of the driver
   • handle the increased backpressure within the system
10. A twin-screw supercharger is used in some applications for its ____________.
    • ability to use a belt to operate the supercharger
    • ability to have a larger power band
    • decreased cost and simpler installation
    • reliable increased power output

ASE Technician A/Technician B–Style Questions

1. Technician A says that a boost leak can cause the intermitted power increase that normally accompanies a forced induction engine. Technician B says foreign objects in the intake tract can help increase the pressure within the engine. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
2. Technician A says that using a Roots-type supercharger will allow for an unlimited amount of boost. Technician B says a twin-screw type of supercharger has a very long power band. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
3. Technician A says that when performing a turbocharger bearing test, there should be some play with the turbine shaft. Technician B says that a failed EGR valve could cause a VGT to stick in one position. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
4. Technician A says that to properly inspect a BOV, the technician should operate the engine in a maximum boost situation. Technician B says that using a scan tool to look at PID data will allow the technician to direct their diagnosis. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
5. Technician A says electronic boost control can be used by the PCM to control how much boost the supercharger can produce. Technician B says that using a water/methanol type of injection system can help to lower combustion temperatures to prevent detonation. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
6. Technician A says an intercooler is used to increase the temperature of the intake air charge. Technician B says that the oil in a supercharger should be changed to prolong the life of the supercharger. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
7. Technician A says the air density of the environment changes with the altitude that it is operating in. Technician B says the volumetric efficiency of a forced induction engine is less than that of a normally aspirated one. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
8. Technician A says that it takes time to build up exhaust pressure, which is called turbo lag. Technician B says that the mechanical components of a forced induction engine need to be more robust than a non–forced induction engine. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
9. Technician A says an overspeeding issue can be caused by a driver not following the speed limit. Technician B says that blue smoke coming out of the tailpipe indicates that the engine is burning oil. Who is correct?
   • Technician A
   • Technician B
   • Both A and B
   • Neither A nor B
10. Technician A says a boost pressure sensor may be located in the engine crankcase. Technician B says that testing for boost leaks is important to verify that the intercooler and piping have been installed correctly. Who is correct?
    • Technician A
    • Technician B
    • Both A and B
    • Neither A nor B