Exhaust manifold

[citation needed] These consist of individual exhaust headpipes for each cylinder, which then usually converge into one tube called a collector.

There are a few types of thermal insulation but three are particularly common: The goal of performance exhaust headers is mainly to decrease flow resistance (back pressure), and to increase the volumetric efficiency of an engine, resulting in a gain in power output.

When an engine starts its exhaust stroke, the piston moves up the cylinder bore, decreasing the total chamber volume.

Many headers are also resonance tuned, to utilize the low-pressure reflected wave rarefaction pulse which can help scavenging the combustion chamber during valve overlap.

For clarification, the rarefaction pulse is the technical term for the same process that was described above in the "head, body, tail" description.

Without an X-H pipe the flow of exhaust would be jerky or inconsistent, and the engine would not run at its highest efficiency.

[5] Today's understanding of exhaust systems and fluid dynamics has given rise to a number of mechanical improvements.

This is achieved by partial closing of an internal valve within the exhaust—the EXUP valve—at the point where the four primary pipes from the cylinders join.

Closing the valve increases the local pressure, thus inducing the formation of larger amplitude negative reflected expansion waves.

At higher speeds the EXUP valve is fully opened and the exhaust is allowed to flow freely.