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Engine knock (detonation) is an important phenomenon, as it sets the upper limit of workable thermal efficiency. Detonation onset depends on several constraints which may well be altered by late intake valve closure. This paper examines the detonation characteristics of two valve closing systems; late intake valve closing versus the conventional one, by analyzing experimental results. It was found that there are some differences in the detonation characteristics of late intake valve closing engine system (LIVCES) and the conventional engine system (CES). The LIVCES enhanced detonation, which had to be compensated by advancing the spark timing. A maximum of 12 CA degrees was found to be the average value necessary to avoid detonation at light-loads. At high-loads the spark timing advance of the LIVCES becomes almost the same as that for the CES. Also, the maximum cylinder pressure was found to be less than that in the CES.