Smaller engine equals more economical car
On paper, a smaller engine will seem more economical for the same size of a car. But you should not try to change your engine to smaller one while thinking it will be more efficient. The car still weighs the same and will cause a duress for an engine and generate additional expenses.
Smaller engines have a higher risk that the engine will work beyond its specified capacity. This problem could cause more fuel consumption, higher running costs and also shorter engine life. Other factors which influence car’s economy is driving style, traffic, maintenance etc.