Cam and compression ratio compatibility
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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==== | ||
| + | If the intake closing (IC) 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 | ||
===Dish volume=== | ===Dish volume=== | ||
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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. | ||
| − | 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 | + | 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: |
| − | *advancing the cam (early IVC) at lower RPM | + | *advancing the cam (early IVC) at lower RPM to produce more torque, less intake reversion, and less lope at idle |
| − | *retarding the cam (late IVC) at higher RPM | + | *retarding the cam (late IVC) at higher RPM to produce more horsepower |
Of course the SCR remains constant despite cam phasing. The DCR will vary based on RPM since this effects intake charge velocity. | Of course the SCR remains constant despite cam phasing. The DCR will vary based on RPM since this effects intake charge velocity. | ||
| − | == | + | ==Compression ratio calculators== |
| + | ===Dynamic compression ratio=== | ||
| + | *[http://www.wallaceracing.com/dynamic-cr.php Wallace Racing DCR calculator] | ||
| + | *[http://www.empirenet.com/pkelley2/DynamicCR.html Kelly DCR calculator] | ||
| + | *[http://www.kb-silvolite.com/calc.php?action=comp2 KB/Silvolite DCR calculator] | ||
| + | *[http://www.rbracing-rsr.com/comprAdvHD.htm RSR DCR calculator] | ||
| − | === | + | ===Static compression ratio=== |
| − | *[http://www.wheelspin.net/calc/calc2.html Static compression ratio | + | *[http://www.wheelspin.net/calc/calc2.html Static compression ratio calculator] |
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==Resources== | ==Resources== | ||
| + | *[[Dynamic compression ratio]] | ||
*[[How to choose a camshaft]] | *[[How to choose a camshaft]] | ||
*[[Camshaft/Compression Ratio relationships]] | *[[Camshaft/Compression Ratio relationships]] | ||
| + | *[[Quench]] | ||
| + | *[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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