In this study, we experimentally investigated the best ignition timing in an SI engine using an E85 ethanol blend by altering the timing angle with respect to gasoline use regarding the output performance parameters such as power and efficiency. We also determined the energy distribution of the engine. The experiments were carried out on a 4-stroke, 4-cylinder spark ignition engine, and the excess air coefficients were almost all maintained at approximately unity. To achieve this, the fuel orifice holes of the carburettor were suitably enlarged for the E85 ethanol blend. The ignition timing was successively delayed in 2 degrees increments up to 6 degrees (denoted as -2, -4, -6, respectively) and then successively advanced by 2 degrees up to 6 degrees (denoted as +2, +4, +6, respectively) with respect to the advance values used with gasoline (called the "original advance values") at full load operation. The best performance and emissions were obtained with +4. Advanced ignition timing resulted in an increase in NOx emissions, while CO and CO2 remained relatively unaffected. Increasing the delay in ignition timing caused poorer combustion and hence more HC emissions and fuel consumption. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.