The effects of a novel pre-combustion chamber design on engine efficiency and emission characteristics were investigated at full and partial loads in the presented experimental and computational study. The original engine was converted to a pre-combustion chambered engine by modifying the cylinder head. Also, a combustion simulation model was developed for the spark ignition engine with pre-combustion chamber and fuelled with natural gas. The experimental performance data of the engine with pre-combustion chamber was compared to theoretical data obtained by using a combustion model. Maximum difference between the experimental results and model data was found lower than 10%. Moreover, it has been observed that the pre-chamber engine is more efficient at low loads and speeds.