Compression Ratio Calculator

Formula

To calculate the Compression Ratio (CR):

\[ CR = \frac{V_s + V_c}{V_c} \]

Where:

\(CR\) is the compression ratio
\(V_s\) is the swept volume
\(V_c\) is the clearance volume

What is Compression Ratio?

The compression ratio of an engine is the ratio between the volume of the cylinder and combustion chamber at the bottom of the stroke and the volume at the top of the stroke. It is a key factor in engine performance and efficiency.

Example Calculation 1

Let's assume the following values:

Number of Cylinders = 4
Bore = 3.5 in
Stroke = 3.5 in
Chamber Volume = 60 cc
Gasket Thickness = 0.04 in
Gasket Bore Diameter = 3.5 in
Deck Clearance = 0.01 in
Piston Volume = 5 cc

Using the formula:

\[ V_s = \pi \times \left(\frac{3.5}{2}\right)^2 \times 3.5 \times 4 = 134.04 \text{ in}^3 \]

\[ V_c = 60 + 5 + \pi \times \left(\frac{3.5}{2}\right)^2 \times 0.04 + \pi \times \left(\frac{3.5}{2}\right)^2 \times 0.01 = 70.24 \text{ cc} \]

\[ CR = \frac{134.04 + 70.24}{70.24} = 2.91 \]

The compression ratio is 2.91.

Example Calculation 2

Let's assume the following values:

Number of Cylinders = 6
Bore = 4.0 in
Stroke = 3.8 in
Chamber Volume = 65 cc
Gasket Thickness = 0.05 in
Gasket Bore Diameter = 4.0 in
Deck Clearance = 0.02 in
Piston Volume = 6 cc

Using the formula:

\[ V_s = \pi \times \left(\frac{4.0}{2}\right)^2 \times 3.8 \times 6 = 286.48 \text{ in}^3 \]

\[ V_c = 65 + 6 + \pi \times \left(\frac{4.0}{2}\right)^2 \times 0.05 + \pi \times \left(\frac{4.0}{2}\right)^2 \times 0.02 = 78.54 \text{ cc} \]

\[ CR = \frac{286.48 + 78.54}{78.54} = 4.65 \]

The compression ratio is 4.65.