Engine Displacement
Total swept volume of all cylinders.
Formula
Variables
Example
b=8.6, s=8.6, n=4: V ≈ 1998 cc (2.0 L)
How it works
Engine displacement is the total volume of air-fuel mixture that all pistons can sweep through as they move from top dead center to bottom dead center. Each cylinder is treated like a simple cylinder-shaped volume, so one cylinder’s swept volume is the cross-sectional area of the bore times the stroke length; multiplying by the number of cylinders gives the whole engine’s displacement. The factor \u03c0/4 comes from the area of a circle, since the piston bore is circular and its area is \u03c0(b/2)^2.
When to use it
Use this formula when you need to estimate or compare engine size from bore, stroke, and cylinder count, such as in engine design, automotive specs, or converting between cubic centimeters and liters. It is also useful for checking whether a stated displacement matches the dimensions of an engine.
Worked example, step by step
Given: b = 7.2 cm, s = 8.4 cm, n = 6 Step 1: Find one cylinder's swept volume: V_cyl = (\u03c0/4) b^2 s V_cyl = (\u03c0/4)(7.2^2)(8.4) V_cyl = (\u03c0/4)(51.84)(8.4) V_cyl \u2248 341.45 cm^3 Step 2: Multiply by the number of cylinders: V = 341.45 \u00d7 6 V \u2248 2048.7 cm^3 Final answer: V \u2248 2049 cc \u2248 2.05 L
Common mistakes to avoid
- Using the bore radius instead of the full bore in the formula
- Forgetting to multiply the single-cylinder volume by the number of cylinders
- Mixing units, such as using bore in mm and stroke in cm without converting first
Did You Know?
A 'square' engine has equal bore and stroke, balancing high-rev breathing against low-end torque.
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