If you put that question into Google, you get an answer saying turbo engines have better mpg, but I remember reading that, during the development of Ford’s 7.3L gasoline engine, they came up with some kind of formula that calculated the most fuel efficient engine for a medium duty vehicle was the N/A 7.3 they ended up with. I’ve also heard it from some of my engineer friends. So what is it?
there are tons of factors that effect mpg. but all things being equal a smaller displacement turbo will be more fuel efficient than the larger engine NA motor, and make more power. you can see this in the current civics… the 1.5t in the Si gets better mpg than the 2.0 in the sport. once you start driving aggressively though the 1.5t is going to making more power by sucking up more air and using more fuel. also, initial response from the engine is going to be slower with a turbo, it takes time to spool up a turbo, which makes it tricky in the corners compared to NA