Some mods can have a detrimental effect to mileage; cams and bad injectors come to mind. Freer exhaust and intake just make it easier for the engine to breathe. It takes a fixed amount of energy to push your car along the highway at a constant 70mph. One of the perks of turbochargers, and why they're becoming more common is that they have a minimal effect on the economy of the engine when the power is not needed.
"Capitalization is the difference between helping your Uncle Jack off a horse, and helping your uncle jack off a horse." "'she' also likes to swap since I think I am going to need to give her to woody again." - Dvlhntr "full alphabetic boost mode" - ChristopherTheOne " Purrs like a sexually satisfied black panther." - BigTDogg "Two oil eating, angry, spinning triangles of death." - turtleboy on rotary engines
