Only 660cc will give you 17-18 in city driving.
Any 1300cc, 1500cc, 1600cc, or 1800cc like 4efe, 5afe, 4afe or 7afe will give you max 12-13km/l in city.
So kindly don't spend on this car if your current engine is fine and don't have any issues.
If you swap 7afe 1800cc ( very expensive now around 150k) it will only give you more power and economy will be same.
If you want boht power and economy get a Prius.