If you look at any car that has 2 available engines, the big engine's gas mileage sucks compared to the small engine. Just as an example, a 2.4L honda accord uses 9.7L of fuel to go 100km while the 3.0L model needs 11.5L of fuel to go that same distance. Since EPA fuel estimates are done under controlled conditions, that means the V6 burns almost 20% more fuel to get the same amount of power. Both cars are tested to accelerate at the same rate, drive the same speed, drive on the same track, and do everything as comparable as possible, but the V6 uses 20% more gas. Why?