Engine Performance & Tuning Flashcards
7 cards from real ABA practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Engine Performance & Tuning flashcards as text
What is the primary advantage of a twin-scroll turbocharger over a single-scroll design?
Answer: Reduced turbo lag and better scavenging
Twin-scroll turbos separate exhaust pulses from cylinder pairs, improving exhaust scavenging and reducing turbo lag by delivering more consistent energy to the turbine.
Which variable in valve timing has the greatest effect on engine torque at low RPM?
Answer: Intake valve closing point
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.
An intercooler primarily improves engine performance by:
Answer: Reducing intake air temperature and increasing air density
Intercoolers cool compressed intake air, reducing its temperature and increasing density, allowing more oxygen per stroke and reducing knock tendency.
What phenomenon occurs when exhaust backpressure causes spent gases to re-enter the cylinder during valve overlap?
Answer: Internal EGR (residual gas trapping)
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.
A wideband oxygen sensor differs from a narrowband sensor in that it:
Answer: Provides accurate lambda readings across a wide AFR range
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.
What is the primary role of a MAP (Manifold Absolute Pressure) sensor in engine management?
Answer: Determine engine load by measuring intake manifold pressure
The MAP sensor measures absolute pressure in the intake manifold, allowing the ECU to calculate air density and engine load to determine appropriate fuel and ignition settings.
Which condition most commonly triggers knock sensor-based ignition retard?
Answer: High engine load combined with low-octane fuel
Knock occurs most readily under high cylinder pressure and temperature conditions, typically high load and high RPM situations, especially when fuel octane is insufficient for the timing map.