Hate to break it to you guys, but BY DEFINITION turbo engines are more efficient than NA or Superchargers (which are by far the worst). So assuming you stuck turbos on your beloved V8s, you'd be getting more power for less cost.
My little V6 is much more powerful than my FIL and my grandfather's new chevys, and they both opted for the big boy V8s. And it gets basically the same gas mileage (when accounting for tires and aerodynamics). They routinely comment how impressive my engine is.
By definition? I'd be careful subscribing to that line of thought. Not by definition ... I think auto manufacturers are in part fooling moronic politicians and policy makers by getting them to focus on displacement numbers, and MPG ratings that are heavily doctored from inaccurate computer calculations, and graphs that are presented to these moron politicians and otherwise who take a quick look at a graph that's put together to push a specific talking point, then go away happy. It's far more complicated than displacement numbers and MPG taken with a driver who uses a straw to blow on the gas pedal, and idles at a stop light for 60 second stints.
Here's a crack at explaining why these small displacement turbo engines are a load of nonsense in the "Eco" devision unless those tiny engines are mated to an equality tiny (and light) vehicle. An under displaced, turbo charged engine on a large heavy truck isn't "Eco". Not saying you don't get great performance out of this engine, you do. But it's not "Eco". Engine performance has come a long way though - compare a 2020 V8 with a 1990's V8 of the same displacement, both naturally aspirated. Major performance increase, and lighter engines by hundreds of pounds.
Why Small Turbo Engines Are Not Efficient