Question 18 MODE01 - Chief MODU Engineer

The Correct Answer is C ### Why Option C is Correct: The valve cam slope angle (often referred to as the flank angle or the steepness of the ramp/slope on the cam lobe profile) directly dictates how quickly the valve lift changes over the degrees of camshaft rotation. * **A steeper slope angle (higher slope)** means the valve is pushed open or allowed to close much faster for a given rotational movement. * **A gentler slope angle (lower slope)** means the process is slower. Since acceleration is the rate of change of velocity, and the speed (velocity) of the valve is changing rapidly during opening and closing, the slope angle fundamentally determines the **acceleration rate of valve opening and closing**. High acceleration rates are necessary to achieve high lift quickly but introduce greater inertia forces and stress on the valvetrain components. ### Why Other Options Are Incorrect: **A) engine torque characteristics:** While the overall valve timing (duration, lift, overlap) heavily influences torque characteristics, the specific slope angle itself is a design parameter focused on managing the mechanical dynamics (acceleration and stress) of the valvetrain, rather than being the primary determinant of the macroscopic torque curve. **B) diameter of intake and exhaust valves:** The physical diameter of the valves is determined by the cylinder bore size, the combustion chamber design, and the desired airflow volume. It is fixed during the engine design phase and is completely independent of the shape (slope angle) of the cam lobe. **D) engine fuel efficiency:** Fuel efficiency is primarily influenced by factors such as compression ratio, air-fuel ratio, combustion stability, and overall valve timing (which affects volumetric efficiency). While an overly aggressive slope angle might require stronger springs and consume slightly more power (reducing net efficiency), it is not the **determinant** of fuel efficiency; that function belongs to the overall timing and lift specifications.