Car Tuning Engine Performance Principles 2 — Questions and Answers
Question 1: What does volumetric efficiency (VE) measure in an engine?
- How efficiently fuel is burned in the combustion chamber
- The ratio of actual air charge to the theoretical maximum the cylinder can hold (Correct answer)
- The percentage of exhaust gas recirculated back into the intake
- The mechanical efficiency of the piston rings sealing the cylinder
Correct answer: The ratio of actual air charge to the theoretical maximum the cylinder can hold
Volumetric efficiency is the ratio of the actual air-fuel mixture drawn into the cylinder versus the cylinder's theoretical maximum volume.
Question 2: Which camshaft specification most directly affects the engine's peak power RPM range?
- Cam lobe base circle diameter
- Valve lift and duration (Correct answer)
- Cam journal diameter
- Lobe separation angle only
Correct answer: Valve lift and duration
Valve lift and duration determine how long and how far the valves open, directly setting the RPM range where the engine makes peak power.
Question 3: What is the primary purpose of a high-flow catalytic converter in a performance build?
- To increase exhaust backpressure for better torque
- To reduce emissions compliance requirements
- To maintain emissions legality while minimizing exhaust restriction (Correct answer)
- To cool exhaust gases before the muffler
Correct answer: To maintain emissions legality while minimizing exhaust restriction
A high-flow cat uses a less restrictive substrate to reduce exhaust backpressure while still meeting emissions standards.
Question 4: What causes detonation (knock) to occur in a gasoline engine?
- The spark plug firing too late in the combustion cycle
- Uncontrolled auto-ignition of the air-fuel mixture before or after the spark event (Correct answer)
- Excessive fuel richness causing unburned hydrocarbons
- Oil contamination in the combustion chamber
Correct answer: Uncontrolled auto-ignition of the air-fuel mixture before or after the spark event
Detonation occurs when heat and pressure cause the air-fuel mixture to self-ignite uncontrollably, creating damaging pressure spikes.
Question 5: How does increasing compression ratio affect an engine's octane requirement?
- Higher compression lowers the octane requirement
- Higher compression has no effect on octane requirement
- Higher compression increases the octane requirement (Correct answer)
- Octane requirement is determined solely by cam timing
Correct answer: Higher compression increases the octane requirement
Higher compression ratios create more heat and pressure in the cylinder, making the mixture more prone to detonation and requiring higher-octane fuel.
Question 6: What is 'scavenging' in the context of engine exhaust tuning?
- Removing carbon deposits from the combustion chamber
- Using exhaust pulse energy to help draw fresh charge into the cylinder (Correct answer)
- Recycling unburned fuel from the exhaust back into the intake
- The process of cooling hot exhaust gases through the muffler
Correct answer: Using exhaust pulse energy to help draw fresh charge into the cylinder
Exhaust scavenging uses the low-pressure wave following an exhaust pulse to help pull fresh air-fuel mixture into the cylinder.
Question 7: In forced induction engines, what is 'intercooler efficiency'?
- The percentage of boost pressure retained after the intercooler
- How effectively the intercooler reduces charge air temperature relative to the maximum possible cooling (Correct answer)
- The ratio of intercooler core volume to engine displacement
- How quickly the intercooler recovers between boost events
Correct answer: How effectively the intercooler reduces charge air temperature relative to the maximum possible cooling
Intercooler efficiency measures how close the outlet charge temperature gets to ambient temperature compared to inlet temperature, expressed as a percentage.
Car Tuning Engine Performance Principles 2
What does volumetric efficiency (VE) measure in an engine?