Enlarged engine control complexity made the full-factorial steady-state testing approach extremely time consuming and hardly applicable under actual industry demands. Slow dynamic slope (SDS) method is one of many approaches with a potential for considerable testing time savings, with its own benefits and drawbacks. This paper puts in focus SDS approach and evaluates its applicability, potentials and accuracy for fast estimation of engine steady-state maps. The presented research is based on an extensive experiment conducted on a small passenger car compresion ignition engine. Being the method that uses quasi-stationary sweeping of the engine, SDS test cycle durations in the range from 120-600 seconds are used in order to test the method and draw conclusions on its applicability. It is shown that well shaped SDS testing cycle can provide a rather good estimate of the steady-state operating points very quickly, with a negligible or very small loss of accuracy. The analysis is conducted both on fast responding variables and those that are heavily influenced by process inertia. This led to some suggestions on how to form a criterion for the SDS gathered data quality evaluation and SDS testing cycle correction.