High speed natural light motion picture records synchronized with head gasket ionization probe and in-cylinder pressure data have been made in the transparent engine of different combustion chamber configurations. For knocking cycles, the head gasket ionization current method simultaneously taken with pressure data was able to find the location of knocking occurrence. To investigate the effects of combustion chamber configurations, the flame propagation experiments for pent-roof combustion chamber with center ignition ( Modified Type I engine ) and modified pent-roof ( Type II engine ) combustion chamber were performed with high speed natural light photography technique. The flame propagation of Modified Type I engine represents more uniform patterns than that of Type II engine. The investigation of knocking combustion was also made possible by observing flame propagation with the measuring techniques that use head gasket ionization probe and in-cylinder pressure data. The numerical simulations of combustion process were also carried out to investigate the in-cylinder flow fields and the flame kernel development. In order to understand the effects of in-cylinder flow on the combustion characteristics in an SI engine, the global combustion submodels were used to consider the laminar kinetic and turbulent mixing effects. The temperature distribution which can be an alternative to predict the flame front was mainly compared with the flame propagation patterns from flame visualization studies.