Dynamic compression ratio
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If the intake closing (IC) point isn't known, it can be calculated by dividing the intake duration by 2, add that to the lobe separation angle (LSA). Then subtract any ground-in advance. Finally, subtract 180. This result does not need to have any amount added, like the KB calculator calls for. | If the intake closing (IC) point isn't known, it can be calculated by dividing the intake duration by 2, add that to the lobe separation angle (LSA). Then subtract any ground-in advance. Finally, subtract 180. This result does not need to have any amount added, like the KB calculator calls for. | ||
| − | DCR and pump gasoline== | + | ==DCR and pump gasoline== |
It's worth mentioning that 8.5:1 DCR is considered to be the maximum for iron heads and 92 octane fuel (MON + RON divided by 2). | It's worth mentioning that 8.5:1 DCR is considered to be the maximum for iron heads and 92 octane fuel (MON + RON divided by 2). | ||
| − | SCR vs. DCR vs. duration== | + | ==SCR vs. DCR vs. duration== |
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: | 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: | ||
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*12.00.......68............8.017........................................................................................................ | *12.00.......68............8.017........................................................................................................ | ||
| + | ==Disclaimer== | ||
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. | 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. | ||
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