toolbox · 03
displacement & compression
displacement from bore and stroke, plus static compression ratio from your chamber, gasket, deck, and piston specs.
Displacement
Litres
2.00
cc
1,998
cubic inches
121.9
Static compression ratio
Uses the bore & stroke above. Piston crown: negative cc for a dome, positive for a dish.
Compression ratio
10.41:1
Swept / cyl
499.6 cc
Clearance / cyl
53.1 cc
how displacement is calculated
displacement is the swept volume of all cylinders: the area of the bore times the stroke, times how many cylinders sweep it.
displacement = π/4 × bore² × stroke × cylinders
a 4.030 inch bore with a 3.480 stroke across 8 cylinders is 355 cubic inches, which is why a 0.030-over 350 gets called a 355.
what static compression ratio actually compares
compression ratio is the cylinder's total volume at bottom dead center divided by what's left at top dead center. the top-dead-center number is the sum of every small volume above the piston: combustion chamber, head-gasket bore, deck clearance, and the piston's dish (or minus its dome).
cr = (swept volume + clearance volume) / clearance volume
clearance = chamber + gasket + deck + piston dish (or − dome)
small volumes swing the answer hard: on a typical small-block, one extra cc of chamber volume moves the ratio by about a tenth of a point. measure, don't assume, if you're building near the pump-gas ceiling.