TORQDEX // ENG-02
Compression Ratio Calculator
Calculate static engine compression ratio using cylinder dimensions, combustion chamber volume, piston volume, head gasket dimensions, and deck clearance.
INPUT DATA
Enter dimensions for one cylinder. Bore, stroke, gasket bore, gasket thickness, and deck clearance are entered in inches. Volumes are entered in cc.
Enter a dish as a positive number and a dome as a negative number.
Positive = piston below deck. Negative = piston above deck.
RESULT
Enter the engine dimensions and chamber volumes.
01 // VOLUME COMPONENTS
What determines compression ratio?
Swept volume
Swept volume is the volume displaced by the piston as it travels from bottom dead center to top dead center. Bore and stroke determine this volume.
Clearance volume
Clearance volume is the space remaining above the piston at top dead center. It includes the combustion chamber, piston dish or dome, gasket volume, and deck volume.
Piston shape
A piston dish increases clearance volume and generally lowers compression ratio. A piston dome reduces clearance volume and generally raises compression ratio.
02 // MEASUREMENT NOTES
Accuracy depends on the inputs
Chamber volume
Published cylinder-head chamber volume is useful for estimates, but measured chamber volume can differ from nominal specifications.
Gasket thickness
Use the manufacturer's compressed gasket thickness, not the uncompressed gasket thickness.
Static vs. dynamic
This calculator determines static compression ratio. Dynamic compression ratio also considers intake-valve closing point and requires additional calculations.
FORMULA
Static compression ratio
Compression Ratio =
(Swept Volume + Clearance Volume)
÷ Clearance Volume
Swept Volume =
π × Bore² ÷ 4 × Stroke
All volumes are converted to cubic centimeters before the final compression ratio is calculated.