Cam and compression ratio compatibility

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(Undo revision 3477941 by 164.90.34.153 (talk))
 
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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
 
|-
 
|-
−
| 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
 
|-
 
|-
−
| 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
+
−
|-
+
−
| 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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An engine having a high performance cam (later IVC point) needs a higher SCR in order to keep the DCR within an optimum range. Because the late IVC point can cause reversion (along with an increase in overlap and/or a tighter LSA), this type of tune can cause the engine to idle rough (have a lot of lope). Idle vacuum will be lower and if you were to put a compression tester on these engines you would see something in the 125-150 PSI range.
 
An engine having a high performance cam (later IVC point) needs a higher SCR in order to keep the DCR within an optimum range. Because the late IVC point can cause reversion (along with an increase in overlap and/or a tighter LSA), this type of tune can cause the engine to idle rough (have a lot of lope). Idle vacuum will be lower and if you were to put a compression tester on these engines you would see something in the 125-150 PSI range.
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====Estimating intake closing point====
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If the intake closing (IC) 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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===Dish volume===
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Most dished pistons have published volumes. Those that don't or with pistons that are unknown as to brand can be estimated by using the following formula:
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{{Note1}}All measurements in inches.
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*3.14 x [radius of the dish]² x depth of the dish x 16.4 (converts cubic inches to cc) = Volume in cc
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**Add 2 or 3cc for the valve reliefs if they extend beyond and/or below the dish.
  
 
===Compression calculators===
 
===Compression calculators===
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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===
 
You can fine tune a particular cam by advancing or retarding it. This procedure does nothing to alter the lift, duration, lobe separation, etc. of the cam. What does happen is the phase of the camshaft is advanced or retarded in relation to the crankshaft position. Advancing the cam closes the intake valve sooner. This will build more pressure in the cylinder and shift the power band lower. Retarding the cam will cause the intake valve to close later, this will build less pressure in the cylinder and shifts the power band higher.
 
You can fine tune a particular cam by advancing or retarding it. This procedure does nothing to alter the lift, duration, lobe separation, etc. of the cam. What does happen is the phase of the camshaft is advanced or retarded in relation to the crankshaft position. Advancing the cam closes the intake valve sooner. This will build more pressure in the cylinder and shift the power band lower. Retarding the cam will cause the intake valve to close later, this will build less pressure in the cylinder and shifts the power band higher.
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Modern engines with '''variable valve timing''' are able to phase the cam while the engine is running. This represents the best of both worlds because the same cam is able to optimize valve events based on engine RPM. This means the VVT engine is capable of:
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*advancing the cam (early IVC) at lower RPM to produce more torque, less intake reversion, and less lope at idle
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*retarding the cam (late IVC) at higher RPM to produce more horsepower
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Of course the SCR remains constant despite cam phasing. The DCR will vary based on RPM since this effects intake charge velocity.
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==Compression ratio calculators==
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===Dynamic compression ratio===
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*[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator]
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*[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly DCR calculator]
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*[http://www.uempistons.com/calc.php?action=comp2 KB/Silvolite DCR calculator]
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*[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>
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{{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
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# Subtract 180
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===Static compression ratio===
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*[http://www.wheelspin.net/calc/calc2.html Static compression ratio calculator]
  
 
==Resources==
 
==Resources==
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*[[Dynamic compression ratio]]
 
*[[How to choose a camshaft]]
 
*[[How to choose a camshaft]]
 
*[[Camshaft/Compression Ratio relationships]]
 
*[[Camshaft/Compression Ratio relationships]]
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*[[Quench]]
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*[http://www.compcams.com/camquest/default.asp Comp Cams CamQuest] dyno simulation program
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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 07:00, 17 July 2023

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