Car Tuning Forced Induction Systems Questions and Answers — Questions and Answers
Question 1: What is the fundamental difference in how a turbocharger and a positive-displacement supercharger derive their power?
- A turbocharger is driven by a belt from the crankshaft, while a supercharger is driven by exhaust gases.
- A turbocharger is driven by exhaust gases, while a supercharger is driven by a belt from the crankshaft. (Correct answer)
- A turbocharger uses an electric motor, while a supercharger uses intake manifold pressure.
- A turbocharger uses intake manifold pressure, while a supercharger is driven by an electric motor.
Correct answer: A turbocharger is driven by exhaust gases, while a supercharger is driven by a belt from the crankshaft.
A turbocharger uses the otherwise wasted energy of hot exhaust gases to spin a turbine, which in turn spins a compressor. A supercharger is mechanically linked to the engine's crankshaft, typically via a belt, and its compressor speed is directly proportional to engine speed.
Question 2: A tuner is pressure testing a newly installed turbo system. They notice that as boost pressure rises with RPM, it eventually exceeds the target set by the wastegate spring and continues to climb. What is the MOST likely function of the component that is failing or improperly configured?
- To cool the compressed air before it enters the engine.
- To lubricate the turbocharger's rotating assembly.
- To control the turbocharger's speed by diverting exhaust gas away from the turbine wheel. (Correct answer)
- To release excess pressure from the intake piping when the throttle closes.
Correct answer: To control the turbocharger's speed by diverting exhaust gas away from the turbine wheel.
The wastegate's primary function is to control the maximum boost pressure by bypassing a certain amount of exhaust gas around the turbine wheel. If the wastegate cannot bypass enough exhaust (due to being stuck, too small, or having a faulty actuator), the turbine will continue to accelerate, causing boost pressure to rise uncontrollably, a condition known as 'boost creep'.
Question 3: A customer's recently modified car with a large turbocharger makes a distinct 'chuffing' or fluttering sound under high-load, low-RPM conditions. The boost gauge needle flickers wildly during these events. Which of the following is the MOST likely cause?
- A boost leak after the throttle body.
- Compressor surge. (Correct answer)
- Normal blow-off valve operation.
- Excessive turbo lag.
Correct answer: Compressor surge.
Compressor surge occurs when the turbocharger produces more pressurized air than the engine can ingest, causing the airflow to reverse back through the compressor. This instability creates the characteristic fluttering sound and erratic boost pressure, and it's most common on large turbos at low engine speeds where airflow is insufficient for the amount of boost being generated.
Question 4: Which of the following is the PRIMARY purpose of installing an intercooler on a vehicle with a forced induction system?
- To increase the temperature of the intake air for better fuel atomization.
- To act as a secondary air filter for the intake charge.
- To muffle the sound produced by the turbocharger or supercharger.
- To cool the compressed intake air, increasing its density and reducing detonation risk. (Correct answer)
Correct answer: To cool the compressed intake air, increasing its density and reducing detonation risk.
The process of compressing air increases its temperature significantly. An intercooler is a heat exchanger that cools this charge air. Cooler air is denser, meaning more oxygen molecules can be packed into each cylinder, allowing more fuel to be burned for more power. It also helps prevent engine knock (detonation) by lowering intake temperatures.
Question 5: A customer with a turbocharged engine that uses a Mass Airflow (MAF) sensor wants to install a valve to vent boost pressure when the throttle closes. To ensure proper engine operation and avoid a rich air-fuel condition, which valve is the correct choice?
- A diverter (bypass) valve that recirculates air back into the intake tract before the turbocharger. (Correct answer)
- A blow-off valve (BOV) that vents the pressurized air to the atmosphere.
- An external wastegate plumbed into the downpipe.
- A manual boost controller installed on the compressor housing.
Correct answer: A diverter (bypass) valve that recirculates air back into the intake tract before the turbocharger.
A MAF sensor measures air entering the intake system. If a blow-off valve vents this already-metered air to the atmosphere, the ECU will inject fuel for air that never reaches the cylinders, causing a temporary rich condition. A diverter or bypass valve solves this by recirculating the vented air back into the intake tract after the MAF sensor but before the turbo compressor, keeping the metered air within the system.
Question 6: Which type of supercharger is characterized by its positive-displacement design, providing instantaneous boost at low engine RPM, but is often less thermally efficient at higher boost levels compared to other designs?
- Centrifugal supercharger
- Exhaust-driven supercharger
- Roots-type supercharger (Correct answer)
- Variable-geometry supercharger
Correct answer: Roots-type supercharger
Roots-type superchargers are a positive displacement design, meaning they move a fixed amount of air per revolution. This results in full boost being available from very low RPMs, providing excellent torque response. However, they tend to generate more heat (are less thermally efficient) compared to centrifugal superchargers, which build boost exponentially with RPM.
Car Tuning Forced Induction Systems Questions and Answers
What is the fundamental difference in how a turbocharger and a positive-displacement supercharger derive their power?