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Basic Cam Terminology
• Ramp - The portion of the cam-lobe event from zero lift (base circle) to the
defined opening or closing point.
• Base-circle radius - The portion of the cam contour at zero lift (valves closed)
• Flank - The section of the cam lobe between the ramp and the nose radius.
• Nose Radius - The radius that is tangent to the flank and the maximum lift point. Also,
the instantaneous radius at the maximum lift point of the nose of the cam.
• Inflection Point - The point on the lift curve where acceleration (of the lifter) changes from
positive to negative or vice versa.
• Main Event - The portion of the cam-lobe profile from the ramp to the nose. There
are two main events - one each for te opening and closing halves of the
profile.
• Velocity - The rate at which position changes. In most instances, it is expressed in
terms of distance versus time (mph, feet per second, etc). When dealing
camshafts, time is replaced by degrees of camshaft rotation.
• Acceleration - The rate at which velocity changes. It is expressed in units of
inch./degree.
• Jerk - How fast the acceleration changes. It is expressed in units of
inch/degree.
• Duration - The amount of time in crankshaft rotational degrees that it takes for a
lifter to travel from a specified lift point on the opening side of the lobe
to the same lift point on the closing side. Unless, you know the specified
lift point, a duration number does not tell you much. Each manufacturer
has a certain standard:
Old Chevrolet spec - .02-inch lifter travel
Aftermarket - .05-inch " "
Advertised - .004-inch " "
SAE - .006-inch " "
• Lobe Centerline - This represents an imaginary line, referenced from the true center of the
base circle out to the end of each lobe, expressed in crankshaft
rotational degrees. Intake-centerline values are found in the crankshaft's
rotation ATDC, while exhaust centerlines are found at travel BTDC.
• Lobe separation angle -Or LSA, is measured in camshaft degrees and refers to the amount of
rotation it takes to travel from the inatke to the exhaust centerline. As
this number grows, the distance betwen the centerlines is spread out.
This is often considered an indicator of overlap, or a period of time
that both valves are open on the same cylinder.
• Base-circle runout - The portion of the cam that is round or the area that defines zero lift.
• Cam factor - This value compares the area of a theoretically ideal cam that would
have a rectangular lobe to the area of lobe being used. A rectangular
lobe would be the perfect design, opening the valve the quickest.
• Area - The summation of the duration multiplied by the lift at each degree. It
It is specified in inch-degree units. This value is used as a lobe-to-lobe
comparitor to determine if they are demensionally similar.
Fundamentals of Camshaft Operation
The following is some helpful information about the events of a typical cam's operation to use as a guideline when considering a cam for your vehicle in order to improve performance, driveability, etc. I have highlighted some points I felt were important to understand and to know in order to grasp the basic problems when designing a camshaft for optimum performance.
Note the graphical representation below to get an idea of how the valve opening and closing points are related to how overlap and timing are created.
Lets first take a look at the 4 opening and closing points:
Intake Opening
Looking at the intake valve first, it's opening point is critical to vacuum, throttle responce, emissions and gas mileage. At low speeds,and high vacuum conditions, premature intake opening during the exhaust stroke can allow exhaust gas reversion back into the intake manifold, hurting the intake pulse velocity, and contaminating the fresh intake charge. A late opening intake gives smooth engine operation at idle and low RPM, plus it ensures adequate manifold vacuum for proper accessory operation ( assuming the other 3 valve opening and closing points remain reasonable).
As RPM increase, air demand is greater. To supply additional air and fuel, designers open the intake valve sooner, which allows more time for the inatke charge to fill the cylinder. With an early opening intake valve, at high rpm, the exiting exhaust gas also helps draw the intake charge thru the combustion chamber and out the exhaust - that's good for purging the cylinder of residual gas, but it also increases fuel consumption by allowing part of the intake charge to escape before combustion and can make for a rough idle.
Intake Closing
The intake closing point has more effect on engine-operating characteristics than any of the other three opening and closing points. The earlier it occurs, the greater the cranking pressure. Early intake closing is critical for low end torque and resonsiveness and provides a broad power curve. It also reduces exhaust emissions while enhancing fuel economy.
As RPM increases, intake charge momentum increases. This results in the intake charge continuing to flow into the combustion chamber against the rising far past BDC. The higher the engine's operating RPM, the later the intake closing should be to ensure all the charge possible makes it into the combustion chamber. Of course, closing the valve too late will create sinificant reversion. It's a fine balancing act.
In a perfect world, the optimum intake closing point would occur just as the air stops flowing into the chamber; it would get the valve seated quickly and not waste time in the low lift regions where airflow is minimal and there is no compression building in the cylinder; it wouldn't be so fast the valve bounces as it closes, allowing the charge to escape back into the inatke port and disturb the next charge; and in hydraulic street cam applications, it would insure that the closing ramps are not so fast that they result in noisy operation.
Exhaust Opening
Overall, the exhaust valve opening point has the least effect on engine performance of any of the four opening and closing points. Opening the exhaust valve to early decreases torque by bleeding off cylinder pressure from the combustion that is used to push the piston down. Yet the exhaust has to open early enough to provide enough time to properly scavenge the cylinder. An early opening exhaust valve may benefit scavenging on high-rpm engines because most useful cylinder pressure is used up anyway by the time the piston hits 90-degrees before BDC on the power stroke. Later exhaust valve opening helps low rpm performance by keeping pressure on the piston longer, plus it reduces emissions.
Exhaust Closing
Excessively late exhaust valve closing is similar to opening the inatke too soon- it leads to increased overlap, allowing either reversion back up the intake, or the intake mixture to keep right on going out the exhaust. On the other hand, late closing events can help purge spent gasses from the combustion chamber and provide more vacuum signal to the intake at high rpm. Early exhaust valve closing yields a smoother operating engine. It does not necessarily hurt the top-end, particularly if it's combined with a later intake valve opening.
As engine operating range increases, designers must move all the opening and closing points out to achieve earlier openings and later closings, or design a more agressive profile to provide increased area under the curve without seat timing increases.
Here is a graph that details a Compcam model and the lobe separation angle vs. crank rotation
Lobe Centerline
Tailoring the valve opening and closing points on an actual camshaft is accomplished by varying the lobe centerline location, changing the LSA, and refining the profile shape itself. We'll consider changing the centerline location first. Advancing the cam moves both the intake and exhaust in an equal amount, resulting in earlier vavle timing events. Engines typically respond better with a few degrees of advance, probably due to the importance of the inrtake closing point on performance. For racing, advanced cams benefit torque converter stall, improve off-the-line drag race launches, and help circle-track cars come off the corner.
Cam companies often grind their street cams advanced (4 degrees is typical), which allows the end-user to recieve the benefits of increased cylinder pressure yet still install the cam using the standard timing marks. One exception is Crane's CompuCam series, which varies because of the vacuum signal requirements of the ECMs it's designed to operate with.
Lobe Separation Angle
Although the installer can advance or retard the lobe centerlines, the separation angle between the centerlines is ground into the cam at the time of manufacture and cannot be changed by the end user. Narrow LSAs tend to increase midrange torque and result in faster reving engines, while wide LSAs result in wider power bands and more peak torque at the price of somewhat lazier initial response.
A street engine with a wide LSA has higher vacuum and a smoother idle. On the street, LSA should be tailored to the induction system inuse. According to Comp Cams, typical carberated, dual plane manifold applications like 110-112 LSAs, while fuel injected combos want slightly wider 112- to 114-degree LSAs. Fuel-injection doesn't require the signal during overlap that carberators need to provide correct fuel atomization, and most computer controllers require the additional idle vacuum that results from decreased overlap.
Bracket racers with higher stall speed converters, higher compression, single-plane intakes, and large carbs usually want 106-110 degree LSAs. Engines equipped with blowers or turbos, or used primarily with Nitrous Oxide, typically work best with wider 110-116 degree separations. Race engine speeds have increased over the years, causing a corresponding upward creep in LSA and duration.
Duration
Duration has a marked affect on a cams's power band and drivalbility. Higher durations increase the top-end at the expense of the low end. A cam's "advertized duration" has been a popular sales tool, but to compare two different cams using these numbers is dicey because there's no set tappet rise for measuring advertised duration. Measuring duration at 0.050-inch tappet lift has become standard with most high-peformance cams. Most engine builders feel that 0.050 duration is closely related to the RPM range where the engine makes it's best power. Typically driven, under 10.25:1 compression ration street machines with standard size carbs, afterarket intakes, headers and recurved ignitions like cams with 0.050-inch duration in the 215- to 230-degree range if using a hydraulic grind, or 230 to 240 degrees with a solid.
When comparing two cams, if both profiles rate the advertized duration at the same lift, the cam with the shorter advertised duration in comparison to the 0.050 duration has a more aggressive ramp. Providing it maintains stable valve motion, the aggressive profile yields better vacuum, increased responsiveness, a broader torque range, and drivability improvements because it effectively has the opening and closing points of a smaller cam combined with the area under the lift curve of a larger cam.
Engines with significant airflow or compression restrictions like aggressive profiles. This is due to the increased signal that gets more of the charge through the restriction and/or the decreased seat timing that results in earlier intake closing and more cylinder pressure.
Big cams with more duration and overlap allow octane-limited engines to run higher compression without detonating in the low to midrange. Conversely, running to big a cam with too low a compression ratio leads to a sluggish response below 3,000 rpm. Follow the cam grinders recomendations on proper cam profile-to-compression ration match-up.
Lift
Another method of improving cam performance is increasing the amount of lobe lift. Designing a cam profile with more lobe lift results in increased duration in the high-lift regions where cylinder heads flow the most air. Short duration cams with relatively high lift can provide excellent responsiveness, great torque, and good power. But high lift cams are less dependable. You need the right valve springs to handle the increased lift, and the heads must be set up to accommodate the extra lift. There are a few examples where increased lift won't improve performance due to decreased velocity through the port; these typically occur in the race engine world (0.650- to 1.00-inch valve lift). Some late model engines with restrictive throttle-body, intake, cylinder head runner and exhaust flow simply can't flow enough air to support higher lift.
Besides grinding a lobe with more lift, you can increase the lift of an existing cam profile by going to a higher rocker arm ratio. For example, small block Chevys where the cylinder head runners are not maxed out may benefit from moving up from the stock 1.5:1 ratio to 1.6:1 rockers. But going up more than one tenth in rocker ratio can lead to trouble; there's a limit to how fast you can move and accelerate the valve before the valve spring can no longer control the system. If a profile was a good design with 1.6:1 rockers, it'll probably be unstable with 1:8.1 rockers. The correct solution is to design the profile from the ground up for use with high-ratio rocker arms.
Overlap
Duration, lift and LSA combine to produce an "overlap triangle". The greater the duration and lift, the more overlap area, LSAs remaing equal. Given the same duration, LSA and overlap are inversely proportional: Increased LSA decreases overlap (and visa versa). More overlap decreases low RPM vacuum and response, but in the midrange, overlap improves the signal provided by the fast moving exhaust to the incoming intake charge. This increased signal typically provides a noticeable engine acceleration improvement.
Less overlap increases efficiency by reducing the amount of raw fuel that escapes thru the exhaust, while improving low-end response due to less reversion of the exhaust gasses back up the intake port; the result is better idle, stronger vacuum signal and improved fuel economy.
Due to the differences in cylinder head, intake and exhaust configuration, different engine combos are extremely sensitive to the camshafts's overlap region. Not only is the duration and area of the overlap important but also its overall shape. Much recent progress in cam design has been due to carefull tailoring of the shape of the overlap triangle. According to Comp Cams, the most critical engine factors for optimizing overlap include intake system efficiency, exhaust system efficiency, and how well the heads flow from the intake toward the exhaust with both valves slightly open.
Asymmetric Lobes
In the past, both opening and closing sides of a cam lobe were identical. Most recently, designers developed asymmetrical lobes, wherein the shape of the opening and closing sides differ. Asymmetry helps optimize the dynamics of a valvetrain system by producing a lobe with the shortest seat timing and the most area. The designer wants to open the valve as fast as possible without overcoming the spring's ability to absorb the valvetrain's inetic energy, then close the valve as fast as possible without resulting in valve bounce. Therea re many different theories about how to design the most aggressive, stable profile.
Hydraulic lifters can provide quiet valvetrain operation only if the closing velocity is kept below a certain threshold. However, the opening velocity can be higher and still provide quiet operation. Almost all modern hydraulic profiles have some symmetry.
Dual-Pattern Cams
If an engine has equal airflow potential on the intake and exhaust sides, a single-pattern cam is sufficient. When airflow differs markedly between the intake and exhaust, a dual-pattern cam should be used to balance flow through the engine. In street applications, they help compensate for a full exhaust system. The amount of difference between the intake and exhaust lobes is based on the cylinder heads characteristics, the intake and exhaust system design, and whether the engine is normally asperated, blown, or nitrous injected.
A recent trend in dual-pattern street cams is to use unique-profile intake and exhaust lobes. Not only does the duration and/or lift of each lobe differ, but the overall lobe shape is specifically optimized for use on the intake or exhaust side. Comp's "Xtreme Energy™" series is as example of this apporach. The intake profiles minimize seat timing and maximize area, and the exhaust profiles promote excellent scavaging, increased signal and maximum flow.
(This is some info that I have taken from articles in various performance magazines. I hope you find it as usefull as I have in
understanding how to select a cam to fit your specific application.) I do not remember were I found this, but I did not write it. I just thought it could help some of our fellow members learn a little about cams.
ENJOY!
• Ramp - The portion of the cam-lobe event from zero lift (base circle) to the
defined opening or closing point.
• Base-circle radius - The portion of the cam contour at zero lift (valves closed)
• Flank - The section of the cam lobe between the ramp and the nose radius.
• Nose Radius - The radius that is tangent to the flank and the maximum lift point. Also,
the instantaneous radius at the maximum lift point of the nose of the cam.
• Inflection Point - The point on the lift curve where acceleration (of the lifter) changes from
positive to negative or vice versa.
• Main Event - The portion of the cam-lobe profile from the ramp to the nose. There
are two main events - one each for te opening and closing halves of the
profile.
• Velocity - The rate at which position changes. In most instances, it is expressed in
terms of distance versus time (mph, feet per second, etc). When dealing
camshafts, time is replaced by degrees of camshaft rotation.
• Acceleration - The rate at which velocity changes. It is expressed in units of
inch./degree.
• Jerk - How fast the acceleration changes. It is expressed in units of
inch/degree.
• Duration - The amount of time in crankshaft rotational degrees that it takes for a
lifter to travel from a specified lift point on the opening side of the lobe
to the same lift point on the closing side. Unless, you know the specified
lift point, a duration number does not tell you much. Each manufacturer
has a certain standard:
Old Chevrolet spec - .02-inch lifter travel
Aftermarket - .05-inch " "
Advertised - .004-inch " "
SAE - .006-inch " "
• Lobe Centerline - This represents an imaginary line, referenced from the true center of the
base circle out to the end of each lobe, expressed in crankshaft
rotational degrees. Intake-centerline values are found in the crankshaft's
rotation ATDC, while exhaust centerlines are found at travel BTDC.
• Lobe separation angle -Or LSA, is measured in camshaft degrees and refers to the amount of
rotation it takes to travel from the inatke to the exhaust centerline. As
this number grows, the distance betwen the centerlines is spread out.
This is often considered an indicator of overlap, or a period of time
that both valves are open on the same cylinder.
• Base-circle runout - The portion of the cam that is round or the area that defines zero lift.
• Cam factor - This value compares the area of a theoretically ideal cam that would
have a rectangular lobe to the area of lobe being used. A rectangular
lobe would be the perfect design, opening the valve the quickest.
• Area - The summation of the duration multiplied by the lift at each degree. It
It is specified in inch-degree units. This value is used as a lobe-to-lobe
comparitor to determine if they are demensionally similar.
Fundamentals of Camshaft Operation
The following is some helpful information about the events of a typical cam's operation to use as a guideline when considering a cam for your vehicle in order to improve performance, driveability, etc. I have highlighted some points I felt were important to understand and to know in order to grasp the basic problems when designing a camshaft for optimum performance.
Note the graphical representation below to get an idea of how the valve opening and closing points are related to how overlap and timing are created.
Lets first take a look at the 4 opening and closing points:
Intake Opening
Looking at the intake valve first, it's opening point is critical to vacuum, throttle responce, emissions and gas mileage. At low speeds,and high vacuum conditions, premature intake opening during the exhaust stroke can allow exhaust gas reversion back into the intake manifold, hurting the intake pulse velocity, and contaminating the fresh intake charge. A late opening intake gives smooth engine operation at idle and low RPM, plus it ensures adequate manifold vacuum for proper accessory operation ( assuming the other 3 valve opening and closing points remain reasonable).
As RPM increase, air demand is greater. To supply additional air and fuel, designers open the intake valve sooner, which allows more time for the inatke charge to fill the cylinder. With an early opening intake valve, at high rpm, the exiting exhaust gas also helps draw the intake charge thru the combustion chamber and out the exhaust - that's good for purging the cylinder of residual gas, but it also increases fuel consumption by allowing part of the intake charge to escape before combustion and can make for a rough idle.
Intake Closing
The intake closing point has more effect on engine-operating characteristics than any of the other three opening and closing points. The earlier it occurs, the greater the cranking pressure. Early intake closing is critical for low end torque and resonsiveness and provides a broad power curve. It also reduces exhaust emissions while enhancing fuel economy.
As RPM increases, intake charge momentum increases. This results in the intake charge continuing to flow into the combustion chamber against the rising far past BDC. The higher the engine's operating RPM, the later the intake closing should be to ensure all the charge possible makes it into the combustion chamber. Of course, closing the valve too late will create sinificant reversion. It's a fine balancing act.
In a perfect world, the optimum intake closing point would occur just as the air stops flowing into the chamber; it would get the valve seated quickly and not waste time in the low lift regions where airflow is minimal and there is no compression building in the cylinder; it wouldn't be so fast the valve bounces as it closes, allowing the charge to escape back into the inatke port and disturb the next charge; and in hydraulic street cam applications, it would insure that the closing ramps are not so fast that they result in noisy operation.
Exhaust Opening
Overall, the exhaust valve opening point has the least effect on engine performance of any of the four opening and closing points. Opening the exhaust valve to early decreases torque by bleeding off cylinder pressure from the combustion that is used to push the piston down. Yet the exhaust has to open early enough to provide enough time to properly scavenge the cylinder. An early opening exhaust valve may benefit scavenging on high-rpm engines because most useful cylinder pressure is used up anyway by the time the piston hits 90-degrees before BDC on the power stroke. Later exhaust valve opening helps low rpm performance by keeping pressure on the piston longer, plus it reduces emissions.
Exhaust Closing
Excessively late exhaust valve closing is similar to opening the inatke too soon- it leads to increased overlap, allowing either reversion back up the intake, or the intake mixture to keep right on going out the exhaust. On the other hand, late closing events can help purge spent gasses from the combustion chamber and provide more vacuum signal to the intake at high rpm. Early exhaust valve closing yields a smoother operating engine. It does not necessarily hurt the top-end, particularly if it's combined with a later intake valve opening.
As engine operating range increases, designers must move all the opening and closing points out to achieve earlier openings and later closings, or design a more agressive profile to provide increased area under the curve without seat timing increases.
Here is a graph that details a Compcam model and the lobe separation angle vs. crank rotation
Lobe Centerline
Tailoring the valve opening and closing points on an actual camshaft is accomplished by varying the lobe centerline location, changing the LSA, and refining the profile shape itself. We'll consider changing the centerline location first. Advancing the cam moves both the intake and exhaust in an equal amount, resulting in earlier vavle timing events. Engines typically respond better with a few degrees of advance, probably due to the importance of the inrtake closing point on performance. For racing, advanced cams benefit torque converter stall, improve off-the-line drag race launches, and help circle-track cars come off the corner.
Cam companies often grind their street cams advanced (4 degrees is typical), which allows the end-user to recieve the benefits of increased cylinder pressure yet still install the cam using the standard timing marks. One exception is Crane's CompuCam series, which varies because of the vacuum signal requirements of the ECMs it's designed to operate with.
Lobe Separation Angle
Although the installer can advance or retard the lobe centerlines, the separation angle between the centerlines is ground into the cam at the time of manufacture and cannot be changed by the end user. Narrow LSAs tend to increase midrange torque and result in faster reving engines, while wide LSAs result in wider power bands and more peak torque at the price of somewhat lazier initial response.
A street engine with a wide LSA has higher vacuum and a smoother idle. On the street, LSA should be tailored to the induction system inuse. According to Comp Cams, typical carberated, dual plane manifold applications like 110-112 LSAs, while fuel injected combos want slightly wider 112- to 114-degree LSAs. Fuel-injection doesn't require the signal during overlap that carberators need to provide correct fuel atomization, and most computer controllers require the additional idle vacuum that results from decreased overlap.
Bracket racers with higher stall speed converters, higher compression, single-plane intakes, and large carbs usually want 106-110 degree LSAs. Engines equipped with blowers or turbos, or used primarily with Nitrous Oxide, typically work best with wider 110-116 degree separations. Race engine speeds have increased over the years, causing a corresponding upward creep in LSA and duration.
Duration
Duration has a marked affect on a cams's power band and drivalbility. Higher durations increase the top-end at the expense of the low end. A cam's "advertized duration" has been a popular sales tool, but to compare two different cams using these numbers is dicey because there's no set tappet rise for measuring advertised duration. Measuring duration at 0.050-inch tappet lift has become standard with most high-peformance cams. Most engine builders feel that 0.050 duration is closely related to the RPM range where the engine makes it's best power. Typically driven, under 10.25:1 compression ration street machines with standard size carbs, afterarket intakes, headers and recurved ignitions like cams with 0.050-inch duration in the 215- to 230-degree range if using a hydraulic grind, or 230 to 240 degrees with a solid.
When comparing two cams, if both profiles rate the advertized duration at the same lift, the cam with the shorter advertised duration in comparison to the 0.050 duration has a more aggressive ramp. Providing it maintains stable valve motion, the aggressive profile yields better vacuum, increased responsiveness, a broader torque range, and drivability improvements because it effectively has the opening and closing points of a smaller cam combined with the area under the lift curve of a larger cam.
Engines with significant airflow or compression restrictions like aggressive profiles. This is due to the increased signal that gets more of the charge through the restriction and/or the decreased seat timing that results in earlier intake closing and more cylinder pressure.
Big cams with more duration and overlap allow octane-limited engines to run higher compression without detonating in the low to midrange. Conversely, running to big a cam with too low a compression ratio leads to a sluggish response below 3,000 rpm. Follow the cam grinders recomendations on proper cam profile-to-compression ration match-up.
Lift
Another method of improving cam performance is increasing the amount of lobe lift. Designing a cam profile with more lobe lift results in increased duration in the high-lift regions where cylinder heads flow the most air. Short duration cams with relatively high lift can provide excellent responsiveness, great torque, and good power. But high lift cams are less dependable. You need the right valve springs to handle the increased lift, and the heads must be set up to accommodate the extra lift. There are a few examples where increased lift won't improve performance due to decreased velocity through the port; these typically occur in the race engine world (0.650- to 1.00-inch valve lift). Some late model engines with restrictive throttle-body, intake, cylinder head runner and exhaust flow simply can't flow enough air to support higher lift.
Besides grinding a lobe with more lift, you can increase the lift of an existing cam profile by going to a higher rocker arm ratio. For example, small block Chevys where the cylinder head runners are not maxed out may benefit from moving up from the stock 1.5:1 ratio to 1.6:1 rockers. But going up more than one tenth in rocker ratio can lead to trouble; there's a limit to how fast you can move and accelerate the valve before the valve spring can no longer control the system. If a profile was a good design with 1.6:1 rockers, it'll probably be unstable with 1:8.1 rockers. The correct solution is to design the profile from the ground up for use with high-ratio rocker arms.
Overlap
Duration, lift and LSA combine to produce an "overlap triangle". The greater the duration and lift, the more overlap area, LSAs remaing equal. Given the same duration, LSA and overlap are inversely proportional: Increased LSA decreases overlap (and visa versa). More overlap decreases low RPM vacuum and response, but in the midrange, overlap improves the signal provided by the fast moving exhaust to the incoming intake charge. This increased signal typically provides a noticeable engine acceleration improvement.
Less overlap increases efficiency by reducing the amount of raw fuel that escapes thru the exhaust, while improving low-end response due to less reversion of the exhaust gasses back up the intake port; the result is better idle, stronger vacuum signal and improved fuel economy.
Due to the differences in cylinder head, intake and exhaust configuration, different engine combos are extremely sensitive to the camshafts's overlap region. Not only is the duration and area of the overlap important but also its overall shape. Much recent progress in cam design has been due to carefull tailoring of the shape of the overlap triangle. According to Comp Cams, the most critical engine factors for optimizing overlap include intake system efficiency, exhaust system efficiency, and how well the heads flow from the intake toward the exhaust with both valves slightly open.
Asymmetric Lobes
In the past, both opening and closing sides of a cam lobe were identical. Most recently, designers developed asymmetrical lobes, wherein the shape of the opening and closing sides differ. Asymmetry helps optimize the dynamics of a valvetrain system by producing a lobe with the shortest seat timing and the most area. The designer wants to open the valve as fast as possible without overcoming the spring's ability to absorb the valvetrain's inetic energy, then close the valve as fast as possible without resulting in valve bounce. Therea re many different theories about how to design the most aggressive, stable profile.
Hydraulic lifters can provide quiet valvetrain operation only if the closing velocity is kept below a certain threshold. However, the opening velocity can be higher and still provide quiet operation. Almost all modern hydraulic profiles have some symmetry.
Dual-Pattern Cams
If an engine has equal airflow potential on the intake and exhaust sides, a single-pattern cam is sufficient. When airflow differs markedly between the intake and exhaust, a dual-pattern cam should be used to balance flow through the engine. In street applications, they help compensate for a full exhaust system. The amount of difference between the intake and exhaust lobes is based on the cylinder heads characteristics, the intake and exhaust system design, and whether the engine is normally asperated, blown, or nitrous injected.
A recent trend in dual-pattern street cams is to use unique-profile intake and exhaust lobes. Not only does the duration and/or lift of each lobe differ, but the overall lobe shape is specifically optimized for use on the intake or exhaust side. Comp's "Xtreme Energy™" series is as example of this apporach. The intake profiles minimize seat timing and maximize area, and the exhaust profiles promote excellent scavaging, increased signal and maximum flow.
(This is some info that I have taken from articles in various performance magazines. I hope you find it as usefull as I have in
understanding how to select a cam to fit your specific application.) I do not remember were I found this, but I did not write it. I just thought it could help some of our fellow members learn a little about cams.
ENJOY!
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