ABA Engine Performance & Tuning 3

Question 1

What is the primary advantage of a twin-scroll turbocharger over a single-scroll design?

Accepted Answer

Reduced turbo lag and better scavenging

Answer

Twin-scroll turbos separate exhaust pulses from cylinder pairs, improving exhaust scavenging and reducing turbo lag by delivering more consistent energy to the turbine.

Question 2

Which variable in valve timing has the greatest effect on engine torque at low RPM?

Accepted Answer

Intake valve closing point

Answer

Retarding intake valve closing (late IVC) improves low-RPM cylinder filling efficiency by allowing the intake charge inertia to continue filling the cylinder after BDC.

Question 3

An intercooler primarily improves engine performance by:

Accepted Answer

Reducing intake air temperature and increasing air density

Answer

Intercoolers cool compressed intake air, reducing its temperature and increasing density, allowing more oxygen per stroke and reducing knock tendency.

Question 4

What phenomenon occurs when exhaust backpressure causes spent gases to re-enter the cylinder during valve overlap?

Accepted Answer

Internal EGR (residual gas trapping)

Answer

When exhaust backpressure exceeds intake pressure during overlap, hot residual exhaust gases flow back into the cylinder, acting as internal EGR and reducing effective volumetric efficiency.

Question 5

A wideband oxygen sensor differs from a narrowband sensor in that it:

Accepted Answer

Provides accurate lambda readings across a wide AFR range

Answer

Wideband sensors use a pumping cell to accurately measure lambda from approximately 0.65 to over 1.6, making them essential for tuning rich or lean mixtures.

(ABA) American Board of Audiology Practice Test

(ABA) American Board of Audiology Practice Test

ABA Engine Performance & Tuning 3