What is the bore of the Mopar 400?
The bore of the Mopar 400 is 4.040 inches (102.6 mm).
The Mopar 400 is the 400 cubic-inch variant of Chrysler’s RB big-block family. It uses a 4.040-inch bore paired with a 3.900-inch stroke to reach its nominal 400 cubic inches of displacement. This combination defined the engine throughout its use in Mopar muscle and full-size cars during the emissions era of the 1970s.
Dimensions and displacement
The following core measurements define the engine’s physical footprint and output characteristics. These values are the factory specifications that enthusiasts reference for rebuilds and performance work.
- Bore: 4.040 inches (102.6 mm)
- Stroke: 3.900 inches (99.1 mm)
- Displacement: 400 cubic inches (6.56 liters)
- Block family: RB (big-block)
- Configuration: V8, pushrod
With these dimensions, the Mopar 400 sits in the middle of the RB lineup, offering more displacement than the 383 while staying lighter than the larger 426/440/Hemi families. The bore size also facilitated parts interchange with other RB cores in many applications.
Production context and variations
The Mopar 400 was produced as part of Chrysler’s RB big-block era, primarily during the 1970s. Emissions controls and year-to-year engineering changes affected factory specifications, but the 4.040-inch bore and 3.900-inch stroke remained the defining dimensions for the 400 cubic-inch variant.
Notes for enthusiasts
When rebuilding or upgrading, many aftermarket blocks keep the 4.040-inch bore, while some stroker kits modify the crank or heads to yield higher displacement. Always verify year- and model-specific data since production adjustments occurred across model lines.
Summary
The Mopar 400’s defining bore is 4.040 inches, paired with a 3.900-inch stroke to yield 400 cubic inches of displacement. This combination, part of Chrysler’s RB big-block family, made the 400 a staple in Mopar muscle cars and trucks during the 1970s, with variations driven by emissions rules and model choices.
