Dynamic Compression Ratio Calculator

Inputs

View results
Cylinder bore diameter.
mm
Piston stroke.
mm
Connecting rod center-to-center length.
mm
Cylinder count for total dynamic displacement.
Combustion chamber volume at TDC.
cm³
Positive for dish or valve reliefs. Negative for dome volume.
cm³
Positive if the piston is below deck at TDC. Negative for pop-up above deck.
mm
Head gasket bore diameter.
mm
Compressed head gasket thickness.
mm
Intake valve closing angle after bottom dead center.
deg ABDC

Results

Default result
Edit inputs
Dynamic compression ratio
7.32
Pass

Dynamic ratio uses the entered intake closing angle and does not predict octane requirement by itself.

Also computed

Static compression ratio8.82

Static geometric ratio from bore, stroke and clearance volume.

Static geometric ratio from the same clearance stack.

Effective strokePass69.43mm

Distance from piston position at intake closing back to TDC.

Effective stroke percent80.74%

Stroke lost after IVC16.57mm

Effective swept volume / cylinder403.3cm³

Clearance volume63.85cm³

Chamber + piston + gasket + deck.

Dynamic compression preview EFFECTIVE STROKE STROKE LOST AFTER IVC 7.32:1 dynamic 80.7% effective stroke
Method notes 3 notes
  • Use advertised or seat intake-closing timing when comparing typical dynamic-compression references. Cam timing at 0.050 in lift usually closes later and can understate trapped stroke.
  • Positive piston volume means a dish or valve relief. Enter a dome as a negative volume.
  • This is a geometry screen only. Detonation margin also depends on fuel, chamber shape, boost, mixture, temperature, quench, altitude and ignition timing.

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