Fig. 5a–d shows the variation of bsfc and brake effective efficiency versus to WR at different loads and engine speeds of 2000, 2500, 3000 and 3500 rpm respectively. Also, at these engine variation ratios of bsfc and effective efficiency were presented in Tables 4–7. It can be seen from these figures and tables that the water injection into intake air does not create any significant change in the bsfc and brake effective efficiency of the engine at selected loads and speeds. As shown in Fig. 5a and b there is a small increase in bsfc with the increase of water percentage at selected loads and at 2000 and 2500 rpm. This trend is quite similar for all of the engine loads.