Dynamic compression ratio
From Crankshaft Coalition Wiki
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| − | + | ==Online calculators== | |
| + | ===Static CR=== | ||
| + | *[http://www.wheelspin.net/calc/calc2.html SCR calculator] | ||
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| + | ===Dynamic CR=== | ||
| + | *[http://www.empirenet.com/pkelley2/DynamicCR.html Dynamic compression calculator] by Kelly | ||
| + | *[https://www.uempistons.com/index.php?main_page=calculators&type=comp&zenid=172b42b3116191725a61237b3da94bb8 Dynamic compression calculator] by KB | ||
| + | *[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator] | ||
| + | *[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator] | ||
| + | {{Note1}} Some dynamic compression ratio calculators (like KBs) ask for an additional 15 degrees of duration be added to the IVC @ 0.050" lift point figure. This works OK on older, slower ramped cam lobes, but the faster lobe profiles may need to have 25 degrees or more added to be accurate.<br> | ||
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| + | {{Note1}}If the intake valve closing (IVC) point isn't known, it can be calculated: | ||
| + | # Divide the advertised intake duration by 2 | ||
| + | # Add the results to the lobe separation angle (LSA) | ||
| + | # Subtract any ground-in advance | ||
| + | # Subtract 180 | ||
| + | This result does not need to have any amount added to the IVC point, like the KB calculator calls for. | ||
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| + | ==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). | ||
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| + | ==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: | ||
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| + | *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........................................................................................................ | ||
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| + | {{Note1}} Disclaimer<br> | ||
| + | Like any other, the Keith Black DCR calculator dynamic compression ratio number is a math caclulation just like SCR - cylinder pressures for identical cam/block configurations may vary based on the total system build from intake to exhaust and hinge largely on volumetric efficiency, valve seat and ring condtion. Cylinder pressures at cranking rpm or at max efficiency rpm differ [tracking volumetric efficiency], therefore two different engines with an identical calculated DCR can have one knock, while the other has no issues for the same octane in the powerband as upper limits of fuel are reached. 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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| + | 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. | ||
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| + | ==Beyond DCR== | ||
| + | There is a limit to what DCR can do. Other concepts have been developed that take this a step (or several steps) further than what DCR is able to accomplish. | ||
| + | *[http://victorylibrary.com/mopar/cam-tech-c.htm#factor Cam Timing vs. Compression Analysis] is an "advanced" formula for looking at the relationship of SCR vs. DCR. In the text the author uses "'''''supra'''''" a lot, it basically means "more info above". | ||
| + | *[http://horsepowerchain.com/ The Horsepower Chain] attempts to put things into a mathematical prospective, and breaks the 4-stroke engine's cycles into 7 distinct segments. | ||
| + | <br><br> | ||
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| + | {{youcanedit}} | ||
| + | [[Category:Engine]] | ||
| + | [[Category:Cylinder head]] | ||
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