With the increasing design potential of computational fluid dynamics to the scavenging process of two stroke cycle engines, a detailed knowledge of the scavenging port efflux flow is essential. This paper describes the design of a two port, two-stroke cycle test cylinder that permits optical access, for laser doppler anemometer measurements, both in the cylinder and at the port boundaries. The Scavenging Efficiency-Scavenge Ratio characteristics of the test cylinder are presented along with measurements of steady state mass flow as functions of port opening and pressure drop across the port. Using laser doppler anemometry, results are presented for the port efflux flow characteristics at different port openings under steady flow conditions. The test results indicate that the flow into the cylinder does not enter in the port design direction at any given port opening. The in-cylinder flow has been modelled using a computational fluid dynamics package. Predicted flowfields, calculated using either measured velocity boundary conditions, or employing the assumptions of plug flow entering in the port design direction, are presented. It is clear that the assumption of plug flow underestimates the short-circuiting potential of the in-coming flow. Theoretical predictions for velocity and turbulence profiles are compared with measurements obtained using LDA.