Originally Posted by Dirty Biker
I think it would get better gas mileage at 4300 rpm at 75-80 mph going down the expressway on flat land than a a 383 or 400 or 454, and would hold up better at that sustained rpm. I travel alot, I drive to Florida, North Carolina, Tennesee, New Mexico, Montana. I need a motor built for 4000+ rpm all day long in this current truck anyway.
And this false assumption is part of why your idea won't work.
A 400sbc making 75hp at 2000 RPM will be operating more efficiently (consuming less fuel) than a 300sbc making 75hp operating at 2700 RPM.