This thesis details an experimental and computational investigation of the relationship between exhaust system geography, the exhaust port pressure history and the gas exchange process in reciprocating four-stroke engines. The study was conducted in four phases. In the first phase, an extensive experimental programme was undertaken, during which key engine performance indicators together with exhaust and intake system manifold pressure and temperature data were recorded on a Rover 1.4 litre 16-valve K series engine. Measured data from each test were used to validate computational predictions. In the second phase the effect of the phasing of pressure waves at the exhaust port was systematically studied using a modified version of the validated model. The relationships between key engine performance indicators and the pressure at the exhaust port during specific periods of the exhaust event were identified. In the third phase, exhaust system gas dynamics were studied and the effect of exhaust system junctions and components on the transmitted and reflected characteristics of pressure waves were investigated. A method was identified by which the dynamic pressure history at the exhaust port could be broken down into its principal incident and reflected pressure wave components.