Cam and compression ratio compatibility

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==Matching cam to compression ratio==
 
Sometimes it's difficult trying to explain to fellows who are new to hot rodding that you have to match the characteristics of the camshaft to the static compression ratio of the motor along with the operating range where the cam makes power. The camshaft is not a stand-alone piece. It must be coordinated with other motor and drivetrain parts in order to arrive at a combination of parts that will all work together toward a common goal.
 
Sometimes it's difficult trying to explain to fellows who are new to hot rodding that you have to match the characteristics of the camshaft to the static compression ratio of the motor along with the operating range where the cam makes power. The camshaft is not a stand-alone piece. It must be coordinated with other motor and drivetrain parts in order to arrive at a combination of parts that will all work together toward a common goal.
  
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<blockquote>With too much compression ratio (or too little duration) the cylinder pressure will be too high, causing pre-ignition and detonation. This condition could severely damage engine components.</blockquote>
 
<blockquote>With too much compression ratio (or too little duration) the cylinder pressure will be too high, causing pre-ignition and detonation. This condition could severely damage engine components.</blockquote>
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{| border="1" cellpadding="2" cellspacing="0"
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{| style="color:black; background-color:#ffffcc;" cellpadding="5" cellspacing="0" border="1"
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|-bgcolor="#DDDFFF"
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!Static Compression Ratio (SCR) !!Intake Valve Duration (degrees @ .050" lift) !!Power Range (RPM)
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!Static Compression Ratio<br> (SCR) !!Intake Valve Duration<br>(degrees @ .050" lift) !!Power Range<br> (RPM)
 
|-
 
|-
−
| align="right" |8.00:1 || align="right" |185º || align="right" |500-4,000
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| align="center" |8.00:1 || align="center" |185º || align="center" |Idle-4,000
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|-bgcolor="#F1F1F1"
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| align="center" |8.25:1 || align="center" |189º || align="center" |Idle-4300
 
|-
 
|-
−
| align="right" |8.25:1 || align="right" |189º || align="right" |650-4300
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| align="center" |8.50:1 || align="center" |194º || align="center" |800-4,500
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|-bgcolor="#F1F1F1"
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| align="center" |8.75:1 || align="center" |200º || align="center" |900-4,600
 
|-
 
|-
−
| align="right" |8.50:1 || align="right" |194º || align="right" |800-4,500
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| align="center" |9.00:1 || align="center" |204º || align="center" |1,000-4,600
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|-bgcolor="#F1F1F1"
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| align="center" |9.25:1 || align="center" |208º || align="center" |1,200-5,200
 
|-
 
|-
−
| align="right" |8.75:1 || align="right" |200º || align="right" |900-4,600
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| align="center" |9.50:1 || align="center" |212º || align="center" |1,600-5,400
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|-bgcolor="#F1F1F1"
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| align="center" |9.75:1 || align="center" |216º || align="center" |1,800-5,600
 
|-
 
|-
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| align="right" |9.00:1 || align="right" |204º || align="right" |1,000-4,600
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| align="center" |10.00:1 || align="center" |221º || align="center" |2,000-5,800
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|-bgcolor="#F1F1F1"
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| align="center" |10.25:1 || align="center" |227º || align="center" |2,400-6,200
 
|-
 
|-
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| align="right" |9.25:1 || align="right" |208º || align="right" |1,200-5,200
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| align="center" |10.50:1 || align="center" |233º || align="center" |2,800-6,400
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|-bgcolor="#F1F1F1"
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| align="center" |10.75:1 || align="center" |236º || align="center" |3,000-6,800
 
|-
 
|-
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| align="right" |9.50:1 || align="right" |212º || align="right" |1,600-5,400
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| align="center" |11.00:1 || align="center" |240º || align="center" |3,200-7,000
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|-bgcolor="#F1F1F1"
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| align="center" |11.50:1 || align="center" |244º || align="center" |3,400-7,200
 
|-
 
|-
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| align="right" |9.75:1 || align="right" |216º || align="right" |1,800-5,600
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| align="center" |12.00:1 || align="center" |248º || align="center" |3,600-7,400
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|-
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−
| align="right" |10.00:1 || align="right" |221º || align="right" |2,000-5,800
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−
|-
+
−
| align="right" |10.25:1 || align="right" |227º || align="right" |2,400-6,200
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−
|-
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−
| align="right" |10.50:1 || align="right" |233º || align="right" |2,800-6,400
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−
|-
+
−
| align="right" |10.75:1 || align="right" |236º || align="right" |3,000-6,800
+
−
|-
+
−
| align="right" |11.00:1 || align="right" |240º || align="right" |3,200-7,000
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−
|-
+
−
| align="right" |11.50:1 || align="right" |244º || align="right" |3,400-7,200
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−
|-
+
−
| align="right" |12.00:1 || align="right" |248º || align="right" |3,600-7,400
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|-
 
|-
 
|}
 
|}
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−
 
 
==Additional reading/engine theory==
 
==Additional reading/engine theory==
 
{{Note1}}  
 
{{Note1}}  
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====Dynamic compression ratio calculators====
 
====Dynamic compression ratio calculators====
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*[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly calculator/info]
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*[http://www.empirenet.com/pkelley2/DynamicCR.html Dynamic compression calculator] by Kelly
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*[http://www.kb-silvolite.com/calc.php?action=comp2 Keith Black calculator]
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*[http://www.uempistons.com/calc.php?action=comp2 Dynamic compression calculator] by KB
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*[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator]
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{{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 nnbfigure. 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.
  
 
===Cam phasing===
 
===Cam phasing===
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*[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator]
 
*[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator]
 
*[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly DCR calculator]
 
*[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly DCR calculator]
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*[http://www.kb-silvolite.com/calc.php?action=comp2 KB/Silvolite DCR calculator]
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*[http://www.uempistons.com/calc.php?action=comp2 KB/Silvolite DCR calculator]
 
*[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator]
 
*[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator]
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{{Note1}} Some dynamic compression rtatio 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.
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{{Note1}}If the intake valve closing (IVC) point isn't known, it can be calculated:
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# Divide the intake duration by 2
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# Add the results to the lobe separation angle (LSA)
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# Subtract any ground-in advance
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# Subtract 180
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This result does not need to have any amount added to the IVC point, like the KB calculator calls for.
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==Compression ratio calculators==
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===Static CR===
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*[http://www.wheelspin.net/calc/calc2.html SCR]
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===Dynamic CR===
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*[http://www.empirenet.com/pkelley2/DynamicCR.html Dynamic compression calculator] by Kelly
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*[http://www.uempistons.com/calc.php?action=comp2 Dynamic compression calculator] by KB
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*[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator]
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*[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator]
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{{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>
 +
 +
{{Note1}}If the intake valve closing (IVC) point isn't known, it can be calculated:
 +
# Divide the intake duration by 2
 +
# Add the results to the lobe separation angle (LSA)
 +
# Subtract any ground-in advance
 +
# Subtract 180
  
 
===Static compression ratio===
 
===Static compression ratio===
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[[Category:Engine]]
 
[[Category:Engine]]
 
[[Category:Camshaft]]
 
[[Category:Camshaft]]
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<pre style="border:none;">
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General Application Chart *
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Advertised
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Camshaft Duration Rear Gear Ratio Engine RPM Range & Compression Ratio Converter RPM Stall Speeds **
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Stock to 260° Stock to 3.23 1000-4600
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8 to 9.5 1500 to 1700
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Stock to 265° Stock to 3.23 1400-5000
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8 to 9.5 1600 to 1800
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265° to 280° 3.00 to 3.73 1600-6000
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9.5 to 10.5 2200 to 2400
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280° to 300° 3.55 to 4.56 2000-6500
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9.5 to 11 3000 to 3400
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280° to 310° 3.73 to 4.88 2800-7000
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10 to 11.5 3500 to 3800
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290°+ 3.73+ 3400-8000
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10.5 to 12 3500+
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</pre>

Latest revision as of 08:00, 17 July 2023

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