Consumption 1.4 and 1.6

Why does the 1.4 consume more fuel than the 1.6? So according to the manual it is always like that. I have a 1.4 with 75 hp and it slabs in about 10 liters. Ok with the curb weight that is no wonder. But why should the 1.6 consume less? That annoys me a little, because I bought the 1.4 extra to be a little more economical. I would like to sell the car again and get me the 90 hp because it has even more power. But first I want your experiences and d Listen to reports. Then I’ll really think about it again. 🙂