[WardL]

I would say in the old days when Ford needed an economical engine with 260 to 351 CI they would use their standard "smaller" engine block design. When Ford wanted more than 360 CI engine with more power, it was most economic/reliable to switch to a heavier duty block, AKA big block design. The added power required the extra strength of the thicker block, etc and the extra weight was more than made up for by the increase in power. As the strength of materials improved and the demand for less weight and more HP for performance, engineers came up with smaller blocks (like the Dart racing block) that could reliably withstand the forces required of 450 CI in a lighter better designed block. The Dart racking block may be referred to a small block, it is much different in terms of strength and reliability. If you take a standard SBF and stroke it to 400 CI, you are taking advantage of the extra capacity Ford wanted in their reliable SB engine. Ford didn't do it, but many Cobra owners have done it and are very happy with the results. It is the same technology advancements we see in every facet of progress. That's my opinion and I'm biased.