What is the bore of the Pontiac 400?
The bore of the Pontiac 400 is 4.12 inches (about 104.6 mm). This dimension, paired with a 3.75-inch stroke, yields the 400 cubic inch displacement that defined a generation of Pontiac muscle cars.
Technical specifications
Core measurements for the Pontiac 400 focus on cylinder bore, stroke, and overall displacement. These figures shaped engine breathing, piston design, and performance characteristics in period Pontiacs.
Bore, stroke and displacement
- Bore: 4.12 inches (approximately 104.6 mm)
- Stroke: 3.75 inches (approximately 95.25 mm)
- Displacement: 400 cubic inches (about 6.6 liters)
These dimensions are associated with the standard Pontiac 400 V8 used in popular models such as the GTO and Firebird during the late 1960s and early 1970s. Variations in production runs and aftermarket components could influence exact tolerances, but the 4.12-inch bore remained the defining specification for the iconic 400 CID engine.
Historical context and usage
During its era, the Pontiac 400 was a staple of the brand’s performance lineup, often matched with aggressive camshaft choices, breathing enhancements, and robust intake and exhaust systems. Its bore size contributed to a characteristic blend of displacement, torque, and streetability that Pontiacs of the period aimed to deliver.
Why bore size matters for performance
The bore size determines how much air and fuel can be brought into each cylinder, influencing combustion chamber shape, piston design, and overall engine efficiency. A 4.12-inch bore, paired with the 3.75-inch stroke, allowed Pontiac to achieve 400 cubic inches while maintaining workable compression and port geometry for performance applications.
Technical nuances and notes
Engine builders and restorers often refer to the 4.12-inch bore as the hallmark specification of the Pontiac 400. While most production units used this standard bore, individual blocks and aftermarket rebuilds may show minor dimensional variations. For enthusiasts seeking authentic rebuilds or precise measurements, checking the block casting numbers and piston dimensions is recommended.
Summary
The Pontiac 400’s defining bore is 4.12 inches, with a 3.75-inch stroke, delivering 400 cubic inches of displacement. This combination helped make the 400 a cornerstone of Pontiac’s performance era, contributing to the high-torque, high-rev potential that defined GTO and Firebird muscle cars.
