Data Source and Methodology
This calculator uses the standard geometric formula for the volume of a cylinder, a fundamental principle in mechanical engineering. The methodology is consistent with industry standards and foundational engineering texts.
- Authoritative Source: Taylor, C. F. (1985). The Internal-Combustion Engine in Theory and Practice, Vol. 1: Thermodynamics, Fluid Flow, Performance. MIT Press.
- Reference: Chapter 1: Engine Types and Their Operation.
All calculations are strictly based on the geometric formulas provided by this and similar core engineering sources.
The Formula Explained
The total displacement of an engine is the sum of the volumes of all its cylinders. The volume (displacement) of a single cylinder is calculated using the formula for a cylinder's volume:
To find the total engine displacement, you simply multiply the volume of one cylinder by the total number of cylinders:
Glossary of Variables
- Bore (B)
- The diameter of the cylinder, or the internal width of the cylinder hole.
- Stroke (S)
- The distance the piston travels up or down within the cylinder, from its lowest point (Bottom Dead Center) to its highest point (Top Dead Center).
- N_cylinders (N)
- The total number of cylinders in the engine (e.g., 4, 6, 8).
- V_cylinder
- The swept volume of a single cylinder.
- V_total
- The total engine displacement, often expressed in Cubic Centimeters (CC) or Cubic Inches (CI).
How It Works: A Step-by-Step Example
Let's calculate the displacement of a common 4-cylinder engine, the Honda K20A, using metric (millimeter) measurements.
- Input Bore: 86 mm
- Input Stroke: 86 mm
- Input Cylinders: 4
- Find the radius:
$ Radius = Bore / 2 = 86 \text{ mm} / 2 = 43 \text{ mm} $ - Calculate single cylinder volume:
$ V_{cylinder} = \pi \times (43 \text{ mm})^2 \times 86 \text{ mm} $
$ V_{cylinder} = 3.14159 \times 1849 \text{ mm}^2 \times 86 \text{ mm} $
$ V_{cylinder} \approx 498,857 \text{ mm}^3 $ - Convert volume to Cubic Centimeters (CC):
Since $ 1 \text{ CC} = 1000 \text{ mm}^3 $, we divide by 1000.
$ V_{cylinder} = 498,857 / 1000 \approx 498.86 \text{ CC} $ - Calculate total displacement:
$ V_{total} = 498.86 \text{ CC} \times 4 \text{ cylinders} \approx 1995.4 \text{ CC} $
The engine's calculated displacement is 1995.4 CC, which is commonly marketed as a "2.0-liter" engine.
Frequently Asked Questions
What is the difference between CC and Cubic Inches (CI)?
CC stands for Cubic Centimeters, a metric unit of volume. CI stands for Cubic Inches, an imperial unit of volume. They both measure the same thing: engine displacement. 1 Cubic Inch is equal to approximately 16.387 Cubic Centimeters.
How does bore vs. stroke affect engine performance?
An 'oversquare' or 'short-stroke' engine (where the bore diameter is larger than the stroke length) generally revs higher and produces more horsepower at high RPM. An 'undersquare' or 'long-stroke' engine (where the stroke is longer than the bore) typically produces more torque at lower RPM.
Is this calculator accurate for 2-stroke and 4-stroke engines?
Yes. The geometric displacement calculation is the same for both 2-stroke and 4-stroke piston engines, as it is based purely on the engine's physical dimensions (bore, stroke, and cylinder count).
Why is my calculated displacement different from the manufacturer's?
Manufacturers often round their advertised displacement for marketing. For example, an engine with a calculated displacement of 1,794 cc might be marketed as a '1.8L' engine. This calculator provides the precise geometric volume based on your inputs.
Does this calculator work for rotary (Wankel) engines?
No. Rotary engines do not use cylinders and pistons. Their displacement is calculated using a completely different method based on the volume of the combustion chambers and is not compatible with this formula.
Tool developed by Ugo Candido. Automotive engineering content reviewed by the CalcDomain Engineering Editorial Board.
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