Engine downsizing of the spark ignition gasoline engine is recognized as one of the most effective approaches to improve the fuel economy of a passenger car. However, further engine downsizing beyond 50% in a 4-stroke gasoline engine is limited by the occurrence of abnormal combustion events as well as much greater thermal and mechanical loads. In order to achieve aggressive engine downsizing, a boosted uniflow scavenged direct injection gasoline (BUSDIG) engine concept has been proposed and researched by means of CFD simulation and demonstration in a single cylinder engine.In this paper, the intake port design on the in-cylinder flow field and gas exchange characteristics of the uniflow 2-stroke cycle was investigated by computational fluid dynamics (CFD). In particular, the port orientation on the in-cylinder swirl, the trapping efficiency, charging efficiency and scavenging efficiency was analyzed in details.Following the CFD analysis, a single-cylinder uniflow 2-stroke research engine was commissioned and successfully operated with spark ignition combustion. The design of the engine is characterized with the compression ratio flexibility, intake port configuration flexibility, port/valve timing flexibility as well as the provision of optical access. The engine was used to carry out in-cylinder flow measurements by the PIV technique. The measured PIV results were then compared with the CFD outputs.