Engine Performance & Tuning Flashcards

What is the stoichiometric air-fuel ratio for gasoline engines?

Answer: 14.7:1

The stoichiometric air-fuel ratio for gasoline is 14.7:1, meaning 14.7 parts air to 1 part fuel for complete combustion.

Which sensor directly measures the mass of air entering the engine?

Answer: MAF sensor

The Mass Air Flow (MAF) sensor directly measures the mass of air entering the intake, allowing the ECU to calculate fuel delivery.

What does advancing ignition timing beyond the optimal point typically cause?

Answer: Engine knock/detonation

Over-advancing ignition timing causes the fuel-air mixture to ignite too early, resulting in knock or detonation that can damage pistons and bearings.

A lambda value of 0.85 indicates the engine is running:

Answer: Rich of stoichiometric

Lambda below 1.0 indicates a rich mixture (excess fuel), while above 1.0 indicates a lean mixture; 0.85 means 15% more fuel than stoichiometric.

What is the primary purpose of a blow-off valve (BOV) in a turbocharged engine?

Answer: Release excess boost when throttle closes

A blow-off valve vents pressurized air from the intake tract when the throttle closes, preventing compressor surge and protecting the turbocharger.

Which compression ratio range is most common for naturally aspirated performance gasoline engines?

Answer: 10:1 to 12:1

High-performance naturally aspirated gasoline engines typically use 10:1 to 12:1 compression ratios to maximize thermal efficiency without requiring extremely high octane fuel.

What does a negative fuel trim value indicate about engine operation?

Answer: The ECU is removing fuel to compensate for a rich condition

Negative fuel trim means the ECU is subtracting fuel from the base map, indicating the engine is running richer than expected and the ECU is compensating.