[Winston]

It is interesting reading about the contrasting theories of "increased Hp/efficiency results in better mpg" ie less restrictive intake or exhaust, or the "reduced hp = greater throttle opening req'd which reduces pumping losses and results in better mpg" ie warm air intake.

As noted, some of those intake and exhaust mods only work with old school, non computerized engines. Less restriction on intake or exhaust does not always equal better efficiency on modern computer controlled engines.