Engine geometry terminology In a “square” engine, which geometric relationship correctly describes the design?

Introduction / Context:
Engine designers use “oversquare,” “undersquare,” and “square” to describe the relationship between cylinder bore and piston stroke. This geometry affects torque characteristics, redline, and packaging.

Given Data / Assumptions:

• Bore = cylinder diameter.
• Stroke = piston travel distance between top and bottom dead centers.
• Square design means bore equals stroke.

Concept / Approach:
When bore = stroke, the ratio bore/stroke = 1. This balance provides a compromise between high-speed breathing (favored by larger bores) and low-speed torque and mechanical advantage (favored by longer strokes).

Step-by-Step Solution:
Define: square → bore = stroke.Match the definition to options.Option d states: “stroke length and cylinder bore are same” → correct.

Verification / Alternative check:
Technical specifications often list bore and stroke; a square engine lists identical dimensions (e.g., 86 mm × 86 mm).

Why Other Options Are Wrong:
Option a misinterprets the term.

Option b compares piston length, which is irrelevant.

Option c describes cylinder arrangement, not geometry.

Option e relates rod length, which varies by design and does not define “square.”

Common Pitfalls:
Assuming square automatically means best performance; cam profiles, intake/exhaust, and combustion design also strongly influence output.

Final Answer:
stroke length and cylinder bore are same