What is the stock bore on a Chevy 350?
The stock bore is 4.000 inches (101.6 mm).
Chevy’s 350 small-block has endured as a foundational engine for cars and trucks since the late 1960s. The 4.000-inch bore, paired with a 3.480-inch stroke, established the familiar 5.7-liter displacement that powered generations of GM vehicles. While the bore is fixed in the factory specification for most Gen I 350s, rebuilding an engine can involve enlarging the cylinders to oversize diameters if wear or damage requires it, which is a common practice among machinists when restoring performance and sealing integrity.
Stock bore size and its role in the 350 family
The standard bore size for the Chevy 350 small-block is 4.000 inches across the majority of production from 1967 onward. This dimension is part of the engine’s core design, contributing to its reliability and aftermarket accessibility. Builders who replace pistons, rings, and other components during a rebuild will typically work within this baseline unless an oversize bore is necessary due to wear or damage.
Rebuilding considerations and oversize options
During a rebuild, machinists measure the current cylinder walls and may choose to bore to an oversize diameter to restore proper clearance and maintain compression. Common oversizes include increments such as 0.010, 0.020, 0.030, and 0.040 inches, resulting in bore diameters of 4.010, 4.020, 4.030, and 4.040 inches. Each oversize requires matching pistons and rings and depends on the block’s condition and the desired displacement. Always verify exact tolerances with the engine block and the parts kit for your specific model year.
Context across generations and variants
The 4.000-inch bore is a defining trait of the Gen I 350 family, which includes a wide range of cars, trucks, and marine applications. While later iterations of the small-block—such as updated generations of the 350—maintained the same basic bore in many configurations, variations in performance, head design, and stroke did occur. In short, the fixed factory bore is the baseline, with rebuilds routinely exploring oversizes to restore performance and reliability.
Summary
The stock bore on a Chevy 350 is 4.000 inches. This standard dimension has underpinned the engine’s versatility and aftermarket compatibility for decades. When rebuilding, engineers may enlarge the bore to oversize measurements if necessary, but the original specification remains the reference point for most Gen I 350s. Always confirm with your block and parts kit to ensure proper fitment and compression.
