The performance and economy of spark ignition engines are, as is well known, adversely affected by the variation in the course of combustion from cycle to cycle, which always occurs to a greater or less extent. In the past decade or so, several investigations of the combustion variation have been made. All these investigations, although differing in detail, have been made on running engines and therefore share certain difficulties in the separation of variables and in interpretation. This paper describes a new experimental approach, using a 1 cycle rig that simulates induction, compression, and combustion phases in a spark ignition engine. Results obtained from it to date are also presented and discussed.