I have heard as a very rough guide, every 100 pounds of extra weight costs you .10 seconds (one tenth of a second) in the quarter mile. It may even be true! I am considering kicking out the heavy bazooka bass tube with separate amp from my car.. it sounded a heck of a lot better in my old 5.0 hatchback than it does in my '98 coupe. Anyway, that's why serious racers strip their cars down to the metal inside, with only one seat; to save every pound they can.