Car Tuning Fuel and Ignition Management 3 — Questions and Answers
Question 1: What is 'MBT' timing in engine tuning?
- Minimum advance for Best Torque — the timing that produces maximum torque without knock (Correct answer)
- Maximum Boost Timing used on forced-induction engines
- Manifold Boost Threshold for supercharger engagement
- Mean Burn Temperature at peak load
Correct answer: Minimum advance for Best Torque — the timing that produces maximum torque without knock
MBT is the optimal ignition advance point that produces the highest torque output; any additional advance risks detonation without further torque gain.
Question 2: A fuel injector is rated at 440 cc/min at 43.5 psi. If rail pressure is raised to 58 psi, how does flow change?
- Flow increases proportionally to the square root of the pressure ratio (Correct answer)
- Flow doubles because pressure doubled
- Flow decreases because the solenoid works against higher pressure
- Flow remains constant because the ECU compensates
Correct answer: Flow increases proportionally to the square root of the pressure ratio
Injector flow scales with the square root of the pressure differential, so a moderate pressure increase yields a modest flow increase, not a linear one.
Question 3: What is the stoichiometric air-fuel ratio for E85 ethanol fuel?
- Approximately 9.8:1 (Correct answer)
- 14.7:1
- 12.5:1
- 6.4:1
Correct answer: Approximately 9.8:1
E85 has a stoichiometric AFR of roughly 9.8:1, requiring significantly more fuel than gasoline's 14.7:1 to achieve complete combustion.
Question 4: What does 'VE table' stand for in standalone ECU tuning?
- Volumetric Efficiency table — a map defining how much air the engine actually ingests vs. theoretical maximum (Correct answer)
- Voltage Enrichment table for cold start fuel
- Variable Exhaust table for cam timing
- Valve Event table controlling VTEC engagement
Correct answer: Volumetric Efficiency table — a map defining how much air the engine actually ingests vs. theoretical maximum
The VE table is the primary fueling map in speed-density systems, representing engine breathing efficiency across the RPM and load axes.
Question 5: Why do high-performance engines often use individual throttle bodies (ITBs) instead of a single throttle body?
- Each cylinder gets its own unrestricted airflow path, improving throttle response and high-RPM VE (Correct answer)
- ITBs allow the ECU to run open-loop fueling only
- They eliminate the need for fuel injectors entirely
- ITBs reduce turbocharger lag on forced-induction builds
Correct answer: Each cylinder gets its own unrestricted airflow path, improving throttle response and high-RPM VE
ITBs remove the shared plenum restriction, giving each cylinder a direct air column that improves high-RPM breathing and sharpens throttle response.
Question 6: What is the function of an ignition coil in a modern direct ignition system?
- To step up battery voltage to tens of thousands of volts needed to arc the spark plug gap (Correct answer)
- To regulate fuel pressure at the common rail
- To control variable valve timing phasing
- To provide reference signal to the crankshaft position sensor
Correct answer: To step up battery voltage to tens of thousands of volts needed to arc the spark plug gap
The ignition coil uses transformer action to convert 12V battery voltage into 15,000–40,000V pulses that reliably jump the spark plug electrode gap.
Question 7: In a speed-density EFI system, which two sensors are primarily used to calculate engine load?
- MAP (manifold absolute pressure) and IAT (intake air temperature) (Correct answer)
- MAF (mass airflow) and throttle position
- O2 sensor and crankshaft position sensor
- Coolant temp and fuel pressure sensor
Correct answer: MAP (manifold absolute pressure) and IAT (intake air temperature)
Speed-density systems use MAP to measure pressure and IAT for air density correction, then combine them with RPM to estimate mass airflow and calculate fuel delivery.
Car Tuning Fuel and Ignition Management 3
What is 'MBT' timing in engine tuning?