Economy

First of all, I'm sure this has been discussed before, so I appologise in advance. But I looked and I looked and didn't find anything (okay I didn't look that much, but that's just because the search tool wasn't very helpful)
I dont get the economy stat on the engines. I mean, g/kwh is pretty self explanatory, but how come my performance engine and my economy engine have similar economies (Maybe because I suck, let me know if thats the case)
To be more specific, here are the engines:
2.0L I6 Turbo with 346HP has an economy of 15,14%
0.9L I4 Turbo with 95HP has an economy of 15,29%
Also, to make things more confusing to me, theres my middle ground engine:
1.5L I4 NA with 88HP has an economy of 17,52%
Sure, this one doesn't have a turbo, but its much bigger than the economy engine and apparently its consuming a lot more. But most of all, how is that 346HP beast consuming the same as my 0.9L shoe box?
I dont get the economy stat on the engines. I mean, g/kwh is pretty self explanatory, but how come my performance engine and my economy engine have similar economies (Maybe because I suck, let me know if thats the case)
To be more specific, here are the engines:
2.0L I6 Turbo with 346HP has an economy of 15,14%
0.9L I4 Turbo with 95HP has an economy of 15,29%
Also, to make things more confusing to me, theres my middle ground engine:
1.5L I4 NA with 88HP has an economy of 17,52%
Sure, this one doesn't have a turbo, but its much bigger than the economy engine and apparently its consuming a lot more. But most of all, how is that 346HP beast consuming the same as my 0.9L shoe box?