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So much to comment on there. The Prius is a lousy reference because it's 1.5L is an old design that was relatively inefficient even when new.
Maximizing any engine's low-RPM torque seems bad for emissions, based solely on the evidence of trends of new cars over the last many years, but torque engines that rev are a lot more fun to drive than engines with more peak HP but less average HP because they have no torque. Sure, a loose torque converter and deep gears can help partially offset that, but the result is still harder to live with. Put the loose converter behind a torque engine that revs, and you have a recipe for excellent fun, with half- throttle tire shredding.
Mileage and emissions don't matter if the car isn't a joy to drive, every mile you drive it. So you may end up at 30 MPG rather than 70, but that still beats the 10 MPG of the musclecar glory years around 1970. And those still were not truly fast, not like today's muscle that can top 30 MPG.
The biggest problem with vvt is that it can't do what is needed. Variable duratuon lifters are a lot closer to ideal.
Exhaust opening, you want early for high rpm power, late for low rpm torque. The same for intake opening. And the exact opposite for valve closing points.
Getting an old school Chevy 350 to make 400 HP and do 30 MPG is easy, no tricks required. With variable duration lifters, 450 HP and 35 MPG looks realistic.
If you could cut one in half, you would get 225 HP, but not 70 MPG. Turbo that up to 450 HP, it should still do more than 35 MPG, so there is merit to boosting smaller engines, but MPG is mostly about aero drag, and for an old V8 car, the rest of it is a mix of dialing in the fuel delivery and spark timing, and getting the cruise rpm down.
And in case i haven't noted it recently, the wilder the cam, the more cruise RPM it needs. That hurts MPG. You want power with your fuel economy? Start with good heads, then add a turbo. That's why the whole world is in love with the LSx. You can have a thousand horsepower with 30 miles per gallon and clean emissions. Work at it, it can do 35 miles per gallon. If you want more MPG and less power, go buy a horse.
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