Car Tuning Engine Performance Principles Questions and Answers

Question 1

Advancing ignition timing typically results in which of the following outcomes?

Accepted Answer

Increased risk of engine knock at high loads

Answer

Advancing ignition timing means the spark plug fires earlier in the compression stroke. While this can increase horsepower, advancing it too far, especially under high load, increases cylinder pressure and temperature, raising the risk of engine knock or detonation.

Question 2

A tuner is aiming for maximum power on a turbocharged gasoline engine. Which air-fuel ratio (AFR) is most appropriate to target under full boost?

Accepted Answer

11.5:1

Answer

Forced induction engines require a richer air-fuel mixture (e.g., around 11.5:1 for gasoline) under boost to help cool the combustion chamber and prevent detonation (knock) caused by the higher cylinder pressures and temperatures. Stoichiometric (14.7:1) is ideal for emissions and cruise, while leaner mixtures are for fuel economy and richer mixtures (to a point) are for power and safety under boost.

Question 3

What is the primary function of a camshaft in determining an engine's performance characteristics?

Accepted Answer

To control the timing, duration, and lift of the intake and exhaust valves.

Answer

The camshaft's lobes dictate the precise moment the intake and exhaust valves open, how long they stay open (duration), and how far they open (lift). This control over the engine's 'breathing' is fundamental to its powerband, torque curve, and overall performance.

Question 4

A customer complains of sluggish turbocharger response and a noticeable loss of power after installing a new, highly restrictive 'quiet' muffler. What is the most likely cause?

Accepted Answer

Excessive exhaust backpressure

Answer

Excessive exhaust backpressure, caused by a restrictive exhaust system, creates resistance that the turbocharger's turbine must overcome. This slows the turbine's speed, reducing its ability to spin the compressor and build boost, leading to turbo lag and a loss of power.

Question 5

Which of the following best defines Volumetric Efficiency (VE)?

Accepted Answer

The ratio of the actual amount of air entering the cylinder to the theoretical maximum amount it could hold.

Answer

Volumetric Efficiency (VE) is a percentage that represents how effectively an engine is 'breathing.' It compares the actual mass of air drawn into a cylinder during the intake stroke to the theoretical volume of the cylinder. Factors like intake manifold design, camshaft profile, and RPM all affect VE.

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Car Tuning Engine Performance Principles Questions and Answers