You may have heard the phrase, there’s no replacement for displacement. In terms of an engine, the displacement is the volume of the cylinder. It is part of what determines how much horsepower and torque an engine can produce. A larger cylinder volume means that the engine is consuming more fuel and therefore producing more power. The opposite is also true. A smaller cylinder volume means less fuel consumption and less power being made.
This can be done through boring and/or stroking an engine block. At a very basic level, bore is the width of a cylinder and stroke is how far the piston can move up and down within the cylinder.
Engine boring is when the cylinder diameter is increased. This is done by machining the walls of the cylinder so that it becomes wider but remains functional. For example, it is not uncommon to bore out the cylinders of a 400 cubic inch engine to make the engine displacement 500 cubic inches.
Stroke is how far the piston travels down the cylinder. To achieve this, there’s really no machining involved. Instead, internal parts such as the piston are simply replaced with a larger version. A popular example of this is a Ford 302 stroked to be a 347. That extra 15% makes a big difference in horsepower!
Stroking is a popular choice among hot rodders for a few reasons. First, there’s no machining involved so less room for error and less downtime. Second, stroking doesn’t change the physical size of the engine so you’re able to fit more power in the same amount of space you originally had.
You don’t necessarily need to pick one over the other. In fact, boring and stroking work best when done together. When doing engine upgrades for our classic car customers, many of them choose bored and stroked engines as opposed to their “stock” counterparts simply because they’re trying to make the most out of what they have.