Engine optimization requires a good understanding of the in-cylinder heat transfer since it affects the power output, engine efficiency and emissions of the engine. However little is known about the convective heat transfer inside the combustion chamber due to its complexity. To aid the understanding of the heat transfer phenomena in a Spark Ignition (S.I.) engine, accurate measurements of the local instantaneous heat flux are wanted. An improved understanding will lead to better heat transfer modelling, which will improve the accuracy of current simulation software. In this research, prototype thin film gauge (TFG) heat flux sensors are used to capture the transient in-cylinder heat flux within a production S.I. engine. A 2-zone temperature model is linked with the heat flux data. This allows the experimental convection coefficient traces to be calculated. The convection coefficient contains all the information of the driving force of the convective heat transfer. Furthermore, the data is split up into different clusters according to the type of flow inside the combustion chamber. The type of flow changes during the engine cycle and this approach allows studying its effect on the convective heat transfer. Some of the existing heat transfer models are based on the Reynolds analogy; this analogy is applied to each cluster to study its overall applicability.