The in-cylinder pressure of internal combustion engines is one of the most important measurable parameter for analyzing the factors affecting performance characteristics of the engine. In many studies, in-cylinder pressure data are averaged over certain number of cycles at each crank angle in order to observe the effects of the parameters. If the number of cycles included is low, then the results may be misleading due to cyclic variations of in-cylinder pressure. The desired level of accuracy can only be obtained if the number of cycles is increased with increasing cyclic variations. The number of cycles used by researchers varies in the literature even for the same subject of study such as research and development, cyclic variations, cycle simulation, etc. There is no general agreement about how many cycle should be taken to obtain the average cycle to remove the effects of cyclic variations. The purpose of this study is therefore to determine the sufficient minimum cycle number at various engine operating conditions on a spark ignition engine by using statistical Levene's test. The results showed that 50 cycles are enough to do accurate calculation of the average pressure cycle at various operation conditions of the engine. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.