🔍 Key Concepts

• Four-stroke cycle timing: intake, compression, power, exhaust • What happens to cylinder pressure near the end of the power stroke • How pumping losses occur during the exhaust stroke

💭 Think About

• Think about the pressure and temperature in the cylinder just before bottom dead center on the power stroke: what happens if you open the exhaust valve at that moment? • How does early opening of the exhaust valve affect how hard the piston has to work to push gases out on the exhaust stroke? • Which of the two statements would be a direct effect of early exhaust opening, and which might be a secondary or not related effect?

✅ Before You Answer

• Be clear on where bottom dead center (BDC) is in the four-stroke cycle and which stroke follows it • Consider whether blow down refers to releasing high-pressure gases early or something else • Ask whether reducing pumping losses is achieved by lowering back pressure, changing valve timing, or both.