http://www.mustangandfords.com/parts/m5lp-1003-2011-ford-mustang-gt-50-coyote-engine/
The Short-BlockBecause a major mandate of the Coyote program was utilizing Ford's existing V-8 mass-production capabilities, and because 5.0 liters was considered the appropriate displacement, the jumping-off point for the Coyote was the closest existing engine, the Three-Valve 4.6 V-8. Bore spacing is critical in the modular engine family-all modulars use 100mm (3.937-inch) bore spacing-because bore spacing and right bank leading are the major non-adjustable features of Ford's block machining line at the engine plant. In fact, bore spacing is likely the defining characteristic of the modular engines. They got the name "modular" because they were conceived in the '80s as a family of engines the assembly plant would sense as nearly identical and thereby allow rapid flexibility in their production. Thus, a modular could be a V or inline four-, six- or eight-cylinder engine, and any one of those engines could be built on Ford's engine lines with just a few hours of change-over time. In some cases similar engines could be built at the same time on the same line in random order, such as is done with 4.6 and 5.4. Given all that, the new 5.0 was going to have a 100mm bore spacing and claim its place as the newest member of the modular family even though in nearly all other respects it is an all-new engine.