My experience bears that out. In the 1970s I drove cars with 36HP. Today I drive a car built in the 70s that has 55hp, and gets about the same mileage even with the advantage of an electronic ignition. 33% more displacement.
I've got a 'modern' stroker 1776 (10% more) mileage motor on the bench that should do better.
Modern because it was built ten years ago.
