What Makes An Engine Better? Big Bore vs Long Stroke Bore and stroke cause differences in both power and efficiency. All piston-cylinder internal combustion engines have a choice to make with regards to bore and stroke. Should an engine have a large bore (the width of the cylinder)? Or would it be beneficial to instead have a small bore and a long stroke? Or should the bore and stroke dimensions of the engine be identical? We'll discuss how bore & stroke affect engine RPM, engine airflow, heat losses with regards to surface area, and flame duration. What makes the most power may not always be the most efficient. With regards to bore and stroke, an engine is called "oversquare" if the bore is longer than the stroke, "square" if the bore and stroke are identical, and "undersquare" if the stroke is longer than the bore.