Todays date is 7/18/2024

Calculate Your Dynamic Compression Ratio

Back to Calculators       Index

(Use seat to seat or advertised specs for Intake spec for best results)
Dynamic Compression Ratio Calculator
Number of Cylinders :
Bore in Inches :
Stroke in Inches :
Rod Length in Inches :
Static Compression Ratio : (:1)   
Inlet Valve Closes ABDC :   °  
Boost Pressure in PSI :
Target Altitude : (Feet)
Input you Bore and Stroke and CR please

Use this calculator to see what the effect of bore, stroke, rod length, cam timing, compression ratio, boost pressure and altitude is on your dynamic compression ratio. Of the variables, the most important is cam timing which has a dramatic effect on your "dynamic" as opposed to your static compression ratio. The more "overlap" your cam has, the lower your "actual" as opposed to your static compression ratio will be. This is one area you can easily change.

Another consideration is rod length and it's effect on the engine's output. Changing the rod length will affect the piston location in the bore relative to cam timing everywhere except at TDC and BDC thus changing the dynamics of the engine.

See this link for information on V/P (Volume/Pressure) Index

V/P Index Calculation

         Dynamic Cranking Pressure: (at 150 rpm starter rpm)
  Note=> after 7 to 10 needle pulses on a hi-quality Compression Tester
         The slower the cranking RPM, the lower the cranking psi
         The faster the cranking RPM, the higher the cranking psi
         The poorer the Piston Ring seal, the lower the cranking psi
         The poorer the Valve Seat (and guide) seal, the lower the cranking psi
         In addition, aluminum Blocks may show lower cranking psi
         Also Engine should be between 140 F to 180 F temperature for Tests

  The compression tester's needle should swing over to 90+ or more psi on the 1st Pulse
  this indicates great Hone Job, Valve Guides, and Valve Job