Hubraum

Hubraum, or engine displacement, is the total volume that is swept by all pistons inside the cylinders of an internal combustion engine during one complete cycle. It is typically expressed in cubic centimeters (cm3) or liters (L), with 1 L equal to 1000 cm3. The displacement of a single cylinder is calculated as pi times the square of half the bore times the stroke; the total engine displacement is the sum for all cylinders.

In practice, hubraum is a primary indicator of engine size. Larger displacement generally enables higher peak torque and power, especially at lower engine speeds, but it also tends to increase fuel consumption and emissions. The relationship is influenced by other factors such as compression ratio, valve timing, induction method, and whether the engine is naturally aspirated or turbocharged.

Modern automotive engineering often uses smaller displacement engines paired with turbochargers or electrified powertrains to achieve comparable performance with improved efficiency. Conversely, high-displacement engines can deliver strong midrange torque without forced induction, but with higher fuel use.

Hubraum is used in marketing, vehicle classification, and sometimes taxation, insurance, and regulatory contexts to distinguish engine sizes. It is a traditional, widely understood metric, though it does not alone determine a vehicle’s overall efficiency or performance.

See also: bore and stroke, torque, power, engine efficiency.