Decarbonization of internal combustion engines can be achieved, among other methods, through the use of carbon-free fuels such as hydrogen or ammonia. Ammonia has been increasingly recognized as a viable alternative engine fuel. This study presents the results of an investigation into the impact of compression ratio on the combustion stability of a naturally aspirated spark-ignition engine fueled with ammonia. The assessment was conducted for three compression ratios: 8, 10, and 12, analyzing changes in the cyclic variability of the IMEP as well as the interdependence between pmax, IMEP, and the crank angle at 50% heat release (CA50). The results demonstrate that ammonia can serve as an effective fuel for SI engines; however, it requires a significantly higher compression ratio compared to conventional hydrocarbon fuels. At a compression ratio of 8, 38 misfire cycles were recorded out of 150 total cycles - representing more than 25% of the dataset. This combustion instability issue was eliminated by increasing the compression ratio.