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Valve timing for a four-stroke petrol engine: exhaust valve events Select the correct typical timing for the exhaust valve opening and closing in a four-stroke petrol engine. Choose the correct option.

Difficulty: Medium

Correct Answer: Opens at 50° before BDC and closes at 15° after TDC

Explanation:

Concept
Typical valve timing uses early exhaust opening (≈ 40–60° before BDC) for blow-down, and exhaust closing slightly after TDC (≈ 10–20°) to aid scavenging and benefit from exhaust inertia.


Why A is right
The given pair (≈ 50° before BDC / 15° after TDC) lies within common textbook values.


Final Answer
Opens at 50° before BDC and closes at 15° after TDC

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