Dynamic compression ratio

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The following are different static compression ratios (SCR) with a 3.48" stroke and different camshaft intake closing points @ 0.050" tappet lift on Keith Black's dynamic compression ratio calculator. The calculator, starting at 8.25:1 SCR. The dynamic compression ratio (DCR) has been kept at just over 8.0:1, a figure that is acceptable for use with today's pump gas with a little cushion:
 
 
*Static CR....Intake closing point @ 0.050"....Dynamic CR.
 
*8.25........10* ABDC......8.010........................................................................................................
 
*8.50........20............8.012........................................................................................................
 
*8.75........27............8.022........................................................................................................
 
*9.00........33............8.018........................................................................................................
 
*9.25........37............8.061........................................................................................................
 
*9.50........42............8.029........................................................................................................
 
*9.75........46............8.016........................................................................................................
 
*10.00.......49............8.038........................................................................................................
 
*10.25.......52............8.043........................................................................................................
 
*10.50.......55............8.029........................................................................................................
 
*10.75.......57............8.069........................................................................................................
 
*11.00.......60............8.022........................................................................................................
 
*11.25.......62............8.038........................................................................................................
 
*11.50.......64............8.042........................................................................................................
 
*11.75.......66............8.035........................................................................................................
 
*12.00.......68............8.017........................................................................................................
 
 
Now, it's unclear where these Keith Black DCR calculator dynamic compression ratio readings are taken; at cranking rpm or at max efficiency rpm. According to the DynoSim software, maximum cylinder pressure is made at or near the torque peak. So, the fact that a motor is not detonating at low rpm does not mean that it will not detonate at, or close to, the torque peak.
 
 
These numbers may not mean anything at all, but they do illustrate that you cannot just pick a cam out of thin air like a lot of fellows do and expect it to work best for your particular combination.
 
 
[[Category:Engine]]
 
[[Category:Cylinder head]]
 

Latest revision as of 07:20, 11 January 2025

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