I think your last thought says it. A 273 was a High Performance engine from the beginning. 318's had to wait till the 80's. All my 273's were balanced and blueprinted. That means every chamber was equalized to within .2 of a cc. TDC was found and marked. Cam was degreed in. Bores were honed with torque plates and mains torqued. They were built when you could readily get 10.5 forged pistons. Theoretical size and horsepower numbers don't add up. A good 273 will hold it's own against anything near it's size and more. A 318 built the same way should be faster, but not by much. But it takes the whole package and attention to detail.
