Compression Ratio Calculator

Calculate engine compression ratio from bore, stroke, chamber volume, head gasket, and piston specifications.

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Engine Preset

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Cylinder Geometry

Cylinder diameter
Piston travel
Swept Volume 499.56 cc/cyl
Displacement 1998 cc (2.00L)
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Clearance Volumes

Combustion chamber volume (from head)
Gasket adds 5.94 cc to clearance
Positive = below deck, Negative = above deck (+0.00 cc)
Positive = dish (adds volume), Negative = dome (removes volume)
9.33 :1
Compression Ratio
Moderate Typical for turbocharged engines

Volume Breakdown

Swept Volume 499.56 cc
Clearance Volume: 59.94 cc
Chamber 50.00 cc
Gasket 5.94 cc
Piston Dish +4.00 cc
Formula: CR = (Swept + Clearance) ÷ Clearance = (499.6 + 59.9) ÷ 59.9 = 9.33

Target Compression Calculator

Calculate what changes are needed to reach a target compression ratio.

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Option 1: Change Chamber Volume

Required chamber: 45.56 cc
Change needed: -4.44 cc

Mill the head surface to reduce chamber volume

Option 2: Change Gasket Thickness

Required gasket: 0.253 mm
Change needed: -0.747 mm

Warning: Gasket too thin, not practical

Understanding Compression Ratio

What is Compression Ratio?

Compression ratio (CR) is the ratio of the total cylinder volume at BDC (bottom dead center) to the clearance volume at TDC (top dead center).

Higher CR generally means more power and efficiency, but requires higher octane fuel and careful tuning.

Typical Compression Ratios

  • 8.0 - 9.0:1 — High boost turbo builds
  • 9.0 - 10.5:1 — Moderate boost or supercharged
  • 10.5 - 11.5:1 — NA performance or low boost
  • 11.5 - 13.0:1 — High performance NA
  • 13.0+:1 — Race engines, E85/methanol

Measuring Chamber Volume

To measure combustion chamber volume accurately:

  • Use a burette with graduated markings
  • Seal spark plug hole with old plug
  • Use a flat piece of plexiglass with a small hole
  • Fill with fluid (alcohol works well) and measure