You are all also leaving out one more important factor... COST. The 5.7L pushrods are produced cheaply. Hell, a Z28 new is still cheaper then half the decent shaped supras out there that are almost 10 years old. Sure many Jap cars pump out high HP from a 4 cyl, but they cost a pretty penny too. Tech takes, money. GM chooses a different route... displacement. I mean I now own a 3SGTE with 20g turbo and a slew of upgrades, but I still don't believe that imports have any "efficiency" over domestics.