What is a 318 engine bored 040 over?

When an engine is "bored over," it means that the cylinders have been enlarged to allow for larger pistons. The number "040" refers to the amount of material that has been removed from the cylinder walls, in thousandths of an inch. So, a 318 engine bored 040 over has had its cylinders enlarged by 0.040 inches.

This process is often done to increase the engine's displacement, which can lead to an increase in power. However, it is important to note that boring over an engine can also weaken the cylinder walls, making it more susceptible to damage. Therefore, it is important to consult with a qualified mechanic before boring over an engine.