Editing Cam and compression ratio compatibility
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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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− | !Static Compression Ratio | + | !Static Compression Ratio (SCR) !!Intake Valve Duration (degrees @ .050" lift) !!Power Range (RPM) |
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− | | align=" | + | | align="right" |8.00:1 || align="right" |185º || align="right" |500-4,000 |
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− | | align=" | + | | align="right" |8.25:1 || align="right" |189º || align="right" |650-4300 |
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− | | align=" | + | | align="right" |8.50:1 || align="right" |194º || align="right" |800-4,500 |
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− | | align=" | + | | align="right" |8.75:1 || align="right" |200º || align="right" |900-4,600 |
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− | | align=" | + | | align="right" |9.00:1 || align="right" |204º || align="right" |1,000-4,600 |
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− | | align=" | + | | align="right" |9.25:1 || align="right" |208º || align="right" |1,200-5,200 |
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− | | align=" | + | | align="right" |9.50:1 || align="right" |212º || align="right" |1,600-5,400 |
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− | | align=" | + | | align="right" |9.75:1 || align="right" |216º || align="right" |1,800-5,600 |
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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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+ | | 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 | ||
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+ | | 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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==Additional reading/engine theory== | ==Additional reading/engine theory== | ||
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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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===Compression calculators=== | ===Compression calculators=== | ||
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====Dynamic compression ratio calculators==== | ====Dynamic compression ratio calculators==== | ||
− | *[http://www.empirenet.com/pkelley2/DynamicCR.html | + | *[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly calculator/info] |
− | *[http://www. | + | *[http://www.kb-silvolite.com/calc.php?action=comp2 Keith Black calculator] |
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===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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==Resources== | ==Resources== | ||
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*[[How to choose a camshaft]] | *[[How to choose a camshaft]] | ||
*[[Camshaft/Compression Ratio relationships]] | *[[Camshaft/Compression Ratio relationships]] | ||
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[[Category:Engine]] | [[Category:Engine]] | ||
[[Category:Camshaft]] | [[Category:Camshaft]] | ||
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