Cause a lot of people can't separate what the factory did performance wise and what's possible with any given engine. Look at 400 ford basically a 4 inch stroked 2bbl Cleveland but most think it has no potential, imagine if there was no 273 and 340 and 318 came with the 273 4bbl package then 340 trim. 318 would of been the legend.
To me I judge mainly by bore
3.625,3.91,4.00,4.04,4.125,4.1875,4.25,4.32,4.34
3.98 is midway, to me 318/340/360 bores are fairly close to each other even a 273 bore is good for at least 400 hp.