Compression Ratio

Written by Jerry Ratzlaff on . Posted in Fluid Dynamics

The compression ratio, abbreviated as CR, a dimensionless number, in an engine is the ratio of the maximum volume to the minimum volume in a cylinder.  The equation and calculator below can help find the compression ratio. 

 

compression ratio calculator

 

 

compression ratio formulas

\(\large{ CR = 1 +  \frac{\pi}{4} \; \frac { BORE^2 \; STROKE }{CCV \;+\; HGV \;+\; PVD  }  }\)  
\(\large{ CR = \frac{ V_d \;+\; V_c }{ V_c }  }\)  

Where:

 Units English Metric
\(\large{ CR }\) = compression ratio \(\large{dimensionless}\)
\(\large{ BORE }\) = bore \(\large{in^2}\) \(\large{mm^2}\)
\(\large{ V_d }\) = clearance volume \(\large{in^3}\) \(\large{mm^3}\)
\(\large{ CCV }\) = combustion chamber volume \(\large{in^3}\) \(\large{mm^3}\)
\(\large{ V_d }\) = displacement volume \(\large{in^3}\) \(\large{mm^3}\)
\(\large{ HGV }\) = head gasket volume \(\large{in^3}\) \(\large{mm^3}\)
\(\large{ \pi }\) = Pi \(\large{3.141 592 653 ...}\)
\(\large{ PDV }\) = piston deck volume \(\large{in^3}\) \(\large{mm^3}\)
\(\large{ STROKE }\) = stroke length \(\large{in}\) \(\large{mm}\)

 

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Tags: Engine Equations Calculators