50 Years of the Small Block

How The Small-Block Got Small...
Ed Cole's objective was to deliver a car that could outperform its archrival from Ford. In a vehicle weighing 3200 to 3400 pounds, a gross power output in the mid- to upper-100-horsepower range was called for, so the team targeted a displacement of around 260 cubic inches. To reduce friction, lower piston speeds, and allow a short engine deck height, his team specified a short-stroke, larger bore (oversquare) design. An innovative crankshaft manufacturing process eliminated the need to provide grinding wheel clearance to each crank arm, shortening the overall length of the five-bearing forged-steel crank to 21.75 inches and suggesting a 4.4-inch bore spacing. Those critical dimensions have defined the small block for a half century.

A 3-3/4-inch bore was selected, and the 2.93-inch stroke that would've yielded 260 cubes was simply rounded to 3.00 inches bringing the original small-block's displacement to 265 cubic inches.

And How It Got Large...

Over the years, small-block displacements have spanned 262.3 to 427.6 cubic inches by combining bores ranging from 3-1/2 to 4-1/8 inches with stroke dimensions between 3 and 4 inches. Seeing that range may lead some to suspect the original was grossly overdesigned, but this isn't the case. Bore increases were not accomplished by machining thick cylinder walls thinner, but rather with new castings that moved the thin cylinder walls out. The 400-cubic-inch small-block of 1970 to 1980 was achieved with a 4-1/8-inch bore that necessitated "siamesing" the cylinders in pairs--that is, casting them with no space for coolant to flow between them. The aluminum Z06's 4-1/8-inch bores employ pressed-in iron liners, each of which has skirts that extend below the cylinder block casting to keep the pistons from falling out of the block at the bottom of their 4.0-inch stroke--the longest-ever in a small-block.