Compression Ratio Calculator

Inputs

Bore (B)

Cylinder bore diameter.

Stroke (S)

Piston stroke.

Cylinders (n)

Cylinder count for total displacement.

Chamber volume (V_ch)

Combustion chamber volume at TDC.

cm³

Piston dish/dome volume (V_p)

Positive for dish or valve reliefs. Negative for dome volume.

cm³

Deck clearance (h_d)

Positive if the piston is below deck at TDC. Negative for pop-up above deck.

Gasket bore (B_g)

Head gasket bore diameter.

Gasket thickness (t_g)

Compressed head gasket thickness.

Default result

Compression ratio

8.82

Pass

Static ratio only; dynamic compression depends on intake valve closing and cam timing.

Also computed

Clearance volume63.85cm³

Chamber + piston + gasket + deck.

Swept volume / cylinder499.6cm³

Total displacement1,998cm³

Gasket volume5.945cm³

Deck volume2.904cm³

Method notes 2 notes

Positive piston volume means a dish or valve relief. Enter a dome as a negative volume.
This is static geometric compression ratio. Octane requirement depends on cam timing, chamber shape, fuel, boost, temperature and tuning.