What is a Compression Ratio Calculator

Compression Ratio Calculator computes the compression ratio of an internal combustion engine, which is the ratio of the total volume to the compressed volume.

It is widely used in automotive engineering to optimize engine performance and efficiency.

How to Calculate Compression Ratio

Input the cylinder bore, piston stroke, number of cylinders, combustion chamber volume, piston volume, head gasket thickness, head gasket bore, and deck clearance. The calculator uses the following formulas:

• Displacement Volume per Cylinder (V_d): \[ V_d = \frac{1}{4} \cdot b^2 \cdot s \cdot \pi \] (where \( b \) is the cylinder bore, \( s \) is the piston stroke, in cm, result in cc)
• Total Displacement Volume: \[ \text{Total } V_d = V_d \times \text{Number of Cylinders} \]
• Head Gasket Volume (V_gasket): \[ V_{gasket} = \frac{1}{4} \cdot g^2 \cdot t \cdot \pi \] (where \( g \) is the head gasket bore, \( t \) is the head gasket thickness, in cm, result in cc)
• Deck Clearance Volume (V_clearance): \[ V_{clearance} = \frac{1}{4} \cdot b^2 \cdot c \cdot \pi \] (where \( b \) is the cylinder bore, \( c \) is the deck clearance, in cm, result in cc)
• Compressed Volume per Cylinder (V_c): \[ V_c = V_{chamber} + V_{piston} + V_{gasket} + V_{clearance} \] (all volumes in cc)
• Compression Ratio per Cylinder (CR): \[ CR = \frac{V_d + V_c}{V_c} \] (result as a ratio, e.g., 10:1)

Click 'Calculate' to see the displacement volume, compressed volume, and compression ratio.

Examples

Example 1: Bore = 100 mm (10 cm), Stroke = 80 mm (8 cm), Number of Cylinders = 4, V_chamber = 50 cc, V_piston = 0 cc, Gasket Thickness = 1 mm (0.1 cm), Gasket Bore = 100 mm (10 cm), Deck Clearance = 0.5 mm (0.05 cm).

Calculation: \( V_d = \frac{1}{4} \cdot 10^2 \cdot 8 \cdot \pi \approx 628.31853 \, \text{cc} \), Total \( V_d = 628.31853 \times 4 \approx 2513.27412 \, \text{cc} \), \( V_{gasket} \approx 7.85398 \, \text{cc} \), \( V_{clearance} \approx 3.92699 \, \text{cc} \), \( V_c \approx 61.78097 \, \text{cc} \), \( CR \approx 11.17118:1 \)

Example 2: Bore = 4 in (10.16 cm), Stroke = 3 in (7.62 cm), Number of Cylinders = 2, V_chamber = 3 cubic in (49.16 cc), V_piston = 0 cc, Gasket Thickness = 0.04 in (0.1016 cm), Gasket Bore = 4 in (10.16 cm), Deck Clearance = 0.02 in (0.0508 cm).

Calculation: \( V_d \approx 609.46897 \, \text{cc} \), Total \( V_d \approx 1218.93794 \, \text{cc} \), \( V_{gasket} \approx 8.22367 \, \text{cc} \), \( V_{clearance} \approx 4.11183 \, \text{cc} \), \( V_c \approx 61.49650 \, \text{cc} \), \( CR \approx 10.91492:1 \)

Enter values and click 'Calculate' to verify.

Frequently Asked Questions (FAQs)

1. What is compression ratio?

Compression ratio is the ratio of the total volume (displacement + compressed) to the compressed volume in an engine cylinder.

2. Why is compression ratio important?

It affects engine efficiency, power output, and fuel economy. Higher ratios generally improve performance but may require higher-octane fuel.

3. What units can I use?

Lengths can be in mm, cm, or inches; volumes can be in cc or cubic inches. The calculator converts all to cm and cc for consistency.

4. What if my piston volume is negative?

A negative piston volume indicates a domed piston that reduces the compressed volume. Enter it as a negative value.