🔍 Key Concepts

• Carefully identify which colored band or shaded area in the diagram represents the intake valve open period versus the exhaust and fuel events. • Note the direction of crankshaft rotation shown by the arrow, and how angles are measured before and after TDC/BDC. • Recall that on a four-stroke engine, the intake valve typically opens before TDC and closes after BDC to use inlet air inertia (valve timing and overlap).

💭 Think About

• Which circular band (outer, middle, or inner) is labeled with the intake stroke, and where along that band does the shading stop as the crank rotates? • Starting from TDC at the beginning of the intake stroke, follow the rotation arrow through BDC: at what angle past BDC does the intake band end? • How do the angle labels (45°, 55°, 75°, 85°) on the diagram line up with the point where the intake shading ends relative to BDC and TDC?

✅ Before You Answer

• Make sure you are reading angles in the same direction as engine rotation, not backwards. • Confirm whether the relevant angle is measured from BDC or TDC; check the text next to the arrow in the diagram. • Verify that the point you pick is where the intake valve just finishes closing (end of the shaded intake band), not where it opens or where another valve event begins.