well im currently doing this mod to my civic... and i expect somewhere in the neighborhood of 12 to 20 horses ...just remember that you never will get what they tell you that you will get... these mods help your car breathe GREAT but.... the fact is more O2 helps but needs more fuel for more combustion... talk to someone about upgrading your fuel system... as well as looking into your ports and do a little grinding... but lol just know what youre doing...