High efficiency engines can be achieved by using high compression ratios and late intake valve closing. In this study, researchers compared engines with these features to a standard engine. They found that engines with over-expanded cycles and high compression ratios had improved efficiency, especially at higher loads. The multi-link engine showed lower knock propensity and better efficiency compared to the high compression engine. Overall, the multi-link engine outperformed the high compression engine and baseline engine in terms of efficiency at various operating conditions.