The basis for Bill Mitchell's affordable big-inch small-block is his proprietary design "Motown" cylinder case--or engine block. The most important aspect of the Motown block is its ability to be bored far larger than there are rings to fit. A 4.175-inch ring size is the largest ring available (normally for a Chrysler) which will leave .225-inch cylinder wall thickness. This produces a 438 cubic inch engine with a 4-inch stroke and a Fel-Pro 1004 head gasket. Theoretically, if there were larger 4.200-inch rings available, you could easily go up to 443 cubic inches and still have a .190-inch cylinder wall thickness.