[morkys]

Some say modding the intake ups fuel use because the increase in air causes more fuel to be injected, in a FI car for instance. I would have thought that for a given throttle opening, more air gets in with less pumping losses when you mod your intake. I figured you'd get more power per unit of fuel burned (due to lower pumping losses), and so as long as you drove properly and conservatively, you would increase fuel economy....but, at least a couple of people have noticed that modded intakes always tend to decrease fuel-economy. Ok, for the purpose of arguement, if we assume modding the intake for higher-flow (as in the typical 'better performance' mods) always increases fuel consumption, then what about exhaust mods?

What about modding the exhaust? I know I could get a header and a slighty larger diameter exhaust, complete with mandrel bent pipes and straight-through muffler etc. All else being essentially equal, will modding the exhaust alone produce an increase in fuel-economy? Or is there another approach to exhaust mods that would increase fuel-economy?