Valve timing in a four-stroke engine Approximately how long (in crank angle degrees) does the inlet valve remain open in a typical four-stroke I.C. engine with conventional timing overlap?

Introduction / Context:
Valve timing diagrams show when intake and exhaust valves open and close relative to piston motion. Due to gas dynamics and inertia, valves open before and close after the ideal geometric points, producing an effective open duration greater than 180° for the intake process in a four-stroke engine.

Given Data / Assumptions:

• Conventional naturally aspirated four-stroke spark-ignition engine.
• Typical timing advance/retard near design speed (some overlap around TDC).
• Representative textbook values are acceptable; exact timing varies with design.

Concept / Approach:

Because the intake valve opens slightly before the intake stroke begins (BTDC) and closes after the piston starts the compression stroke (ABDC), the crank-angle duration exceeds the geometric 180°. Typical combined advance and late closing sums to about 50° (e.g., 15–20° BTDC opening and 30–40° ABDC closing), giving roughly 230° total open duration.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturer timing charts and classic examples routinely show intake durations in the 210–250° range, with 230° a common rounded teaching value.

Why Other Options Are Wrong:

180° ignores advance/retard effects; 130° is far too short; 270° is unusually long for typical production engines.

Common Pitfalls:

Confusing cam duration (at a given lift) with valve-event crank angles; also, performance cams may differ significantly.

Final Answer:

230°