A numerical and experimental study on performance and emission characteristics of four-stroke, four-cylinder Multi Point Injection (MPI) engine operating on iso-butanol/gasoline blends was carried out. The study aims at extending the widely used Wiebe function to combustion modeling of alternate fuels. Quasi one-dimensional simulation and experiments were carried out for different blends of iso-butanol and gasoline (0% (pure gasoline), 10% (IB10), 20% (IB20), 30% (IB30), by volume of iso-butanol) at wide open throttle (WOT) condition for five engine speeds in the range of 2000 to 4000 rpm. The computational and experimental results complement each other validating the proposed extension. BSFC of the blends initially drops for IB10 and later rises with increase in concentration of iso-butanol. Compared to gasoline, the blends lead to considerable decrease in the amount of unburned hydrocarbons (HC) and no change of carbon monoxide (CO). However, there is considerable increase in the amount of oxides of nitrogen (NOx).