Dynamic compression ratio

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(New page: Just for grins, I calculated different static compression ratios with a 3.48" stroke and different camshaft intake closing points @ 0.050" tappet lift on Keith Black's dynamic compression ...)
 
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Just for grins, I calculated different static compression ratios 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 went ka-flooey on 8.00, so we'll start at 8.25 SCR. I kept the DCR at just over 8.0, a figure that is well accepted for operation of the motor on pump gas with a little cushion...
 
  
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Static CR....Intake closing point @ 0.050"....Dynamic CR
 
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8.25........10* ABDC....8.010
 
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8.50........20..............8.012
 
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8.75........27..............8.022
 
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9.00........33..............8.018
 
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9.25........37..............8.061
 
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9.50........42..............8.029
 
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9.75........46..............8.016
 
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10.00......49..............8.038
 
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10.25......52..............8.043
 
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10.50......55..............8.029
 
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10.75......57..............8.069
 
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11.00......60..............8.022
 
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11.25......62..............8.038
 
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11.50......64..............8.042
 
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11.75......66..............8.035
 
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12.00......68..............8.017
 
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Now, it's unclear where these dynamic cr readings are taken, at cranking rpm's or at max efficiency rpm's. But I can tell you this from playing with the DynoSim, max cylinder pressures are made at or near the torque peak. So, the fact that a motor is not detonating at low rpm's does not mean that it will not detonate at or close to the torque peak.
 
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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.
 

Latest revision as of 07:20, 11 January 2025

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