What it a Chevy 350 bored 040?

A Chevy 350 bored .040" is a 350 cubic inch small-block Chevrolet V8 engine that has had its cylinders enlarged by 0.040 inches (40 thousandths of an inch) in diameter during a machining process called boring. This increases the engine's displacement slightly, resulting in a small increase in power and torque. The .040" overbore is a common modification.