Basic Engine Calculations
Displacement is the amount of volume that is displaced as the piston are moved from the top of the stroke to the bottom of the stroke.
Displacement = bore2 x .0007854 x stroke x #of cylinders
Bore and stroke in mm.
Displacement in cc, divide by 1000 to get litre(s).
Compression Ratio (CR)
The static CR is the pressure ratio between the uncompressed air fuel mixture when the stroke is at BDC (bottom dead center) and the compressed air fuel mixture when the stroke is TDC (top dead center).
CR = (V + H) H
H is chamber volume. Chamber volume is the volume of the head per cylinder minus piston volume (above deck height). V= bore2x .0007854 x stroke
Chamber volume if CR is known
If Compression Ratio (CR) is known the CR equation can be re-arranged to find chamber volume (H).
H = V (CR-1)