The expansion chamber is designed to produce a negative pressure wave to assist in filling the cylinder with the next intake charge, and then to produce a positive pressure wave which reduces the amount of fresh intake charge that escapes through the exhaust port (port blocking).
The timing of the exhaust valve closure is designed to assist in filling the cylinder with the next intake charge (as per four-stroke engines).
The pipe lengths and merging locations are designed to assist in filling the cylinder with the next intake charge using exhaust scavenging.
The diameters of the exhaust system are designed to minimise back-pressure by optimising the gas velocity.
[5][6] Even spacings of 360-360 degrees are only possible if a cross-over exhaust manifold is used to pair cylinders from separate banks.
[7] However, the gases tend to cool as they pass through longer pipes, which reduces the effectiveness of the catalytic converter.