Scavenging (automotive)

Uniflow scavenging

For other uses, see Scavenger (disambiguation).

In automotive usage, scavenging is the process of pushing 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 combustion engine. Modifying the exhaust system, (i.e. modifying the exhaust gas velocity by changing exhaust tube diameters) can detract from the "ideal" scavenging effects, and reduce fuel efficiency and power if not properly planned out and executed.

To increase scavenging potential, the entire path from intake to exhaust (i.e. all powertrain parts) to tailpipe must be tuned in sync with each other. This will ensure that the air flow is never interrupted. The acceleration and deceleration of this exhaust gas is what will hinder the scavenging potential.

For example, fast flowing heads and a tunnel ram intake combined with a badly planned camshaft and exhaust system will cause the air to "slow down" and "speed up" throughout its journey, thus reducing its scavenging potential. So, to increase scavenging potential, the air must maintain a positive linear acceleration curve.

There are three types of scavenging on the basis of the flow of air:

1. Direct or cross scavenging
2. Loop scavenging, using Schnuerle porting
3. Uniflow scavenging

See also

• Engine tuning
• Inertial supercharging effect
• Kadenacy effect
• Reciprocating engines