Scavenging consists of pushing the exhausted gas-charge out of the cylinder, and drawing in a fresh draught of air ready for the next cycle.

This process is essential in having a smooth running internal comobustion engine. By modifying the exhaust system, (i.e. modifying the back pressure) you can infact detract from the 'ideal' scavenging effects, and reduce fuel efficiency and power.

See Reciprocating engines or see Cylinder (engine). Components of a typical, four stroke cycle, DOHC piston engine. ... A piston and cylinder from a steam engine A cylinder in an internal combustion engine is the space within which a piston travels. ...