On gas mileage you have to remember the new cars with computers and EFI can control fuel mixture and timing so closely to get about 14 to 1 ratio at all times for good mileage and great eng power through all rpm ranges. Its unreal how fast the new technology works on the computers of todays cars. And the engines are built to take more power then the older muscle car era engines. I mean the Hellcat bottom end can handle well over 700 hp with stock parts. And the technology of the turbo and superchargers of today are so much better then the 70's that they can sell supercharged engines with great power that stay together. But as was said the biggest power maker of today is the boosting of engines. Supercharging adds so much more power its unreal. Take a SRT-8 Challenger or Scat Pack Challenger today and it should run mid to high 12's all stock with a good tire. Add the supercharger and run high 10's on a good tire. I remember some years back Mopar Muscle dyno'd a crate 360 eng at 359 hp. They added a supercharger to it and still used a carb and with 8 lbs of boost were over 600 hp as it nearly doubled the eng hp ! But I still love building the older engines with some newer parts like aluminum heads and making some good hp N/A. Ron