Variable Compression Ratio engine test rig is used to determine the effect of compression Ratio on the performance and emissions of the engine. The objective is to determine the optimum compression ratio for the better performance and lowering the emissions. In order to determine the optimum compression ratio, experiments were carried out on a single cylinder four stroke variable compression ratios of 16.5, 17.0, 17.5, 18.0 and 19.0 in a Diesel engine. The performance characteristics of the engine namely break power, brake thermal efficiency, brake specific fuel consumption and other parameters are studied and also conducted the emissions test namely Carbon monoxide, carbon dioxide, hydrocarbons, Nitrogen oxides and other emissions at various conditions. It is observed that a significant improvement in the performances and lowered the various emissions also at a compression ratio of 17.0 compared to other compression ratios due to the enhancement of the overall combustion process.