🔍 Key Concepts

• Exhaust back pressure and how it affects the flow of burned gases out of the cylinder • How scavenging (clearing exhaust and filling with fresh air) works in a four-stroke diesel • Relationship between back pressure, engine breathing, and power/mean effective pressure

💭 Think About

• Think about what happens if it becomes harder for exhaust gases to leave the cylinder. Does the cylinder empty more or less completely? • If hot exhaust gases remain in the cylinder, how might that affect the amount of fresh air (oxygen) that can enter on the intake stroke? • Consider whether increasing resistance in the exhaust path would generally help or hurt engine efficiency and power output.

✅ Before You Answer

• Be clear on the difference between mean effective pressure in the cylinder and back pressure in the exhaust system • Decide whether more exhaust restriction helps or harms scavenging in a four-stroke engine • Ask yourself: if the engine breathes less freely, would that tend to increase or decrease horsepower?