If you are thinking of modifying your Impreza one thing check is that you have the appropriate injectors for the power you envisage. The following table illustrates the theoretical maximum BHP for different size injectors running at 100% duty cycle on a 4-cylinder engine. Use this as a guide when planning your modifications.
Note, if you change the size of your injectors you _will_ need to remap your ECU.
|Injector Size||BHP @3bar fuel press||BHP @3.5bar fuel press|
Information source - SIDC form thread Injectors