power plus gas milage

well IF it was available

aluminum heads, which would give you lower weight and allow higher compression ratio.

just cutting weight alone increases mileage. higher compression burns fuel more efficiently, getting more power from the same amount of fuel.

other things to cut weight.... there is a ton you can do. one bad mistake many make is larger tires which usually reduces your mileage. (they not only weigh more but higher rotational mass also, so more hp is lost turning them)

good tune up... fresh plugs / wires etc gives better mileage

fresh oil changes = keep oil clean

dont buy into some of the advertising crap: increasing spark is one. you might gain .00005% or somthing. just having clean spark plugs will do the trick. or the K&N air filter crap... just run clean filters. more times than not the K&N people are running them dirty and gummed up and engine is running rich and wasting gas.

get rid of roof racks, spoilers, other stuff that increases drag.

dont use the A/C if you can avoid it. taking it off the car (unless you live down south) cuts weight and reduces drag on the engine.

dont go dual exhaust .... get a large single exhaust, it will weigh less than a dual. headers can help also, they weigh less and restrict the motor less.