GokuSSJ4
05-03-2005, 12:10 PM
what you need to know before you buy cams and what they do.
Power Tech: Camshafts
Among all the components that make up an engine, the camshaft plays the most significant role in determining the behavior and character of the engine. As for the engine's behavior, most OEM camshafts offer idles that are smooth and polished. A radical aftermarket full-race camshaft may produce an idle that is rough and raw. As for character, one camshaft may regulate an engine to produce massive low-end torque, while a different camshaft in that same engine may soften up the power production at the low end while allowing the engine to pull strong up to redline. Understanding the function, design, and limitations of the camshaft will allow you to maximize your performance experience.
Function of the Camshaft
The four-stroke process that occurs in your car's engine is as follows: intake, compression, power, exhaust. While the crankshaft's position, crankshaft's stroke and rod length ultimately determine where the piston will be in the cylinder at any given degree of rotation, it's the camshaft that determines the position of the intake and exhaust valve during all four strokes. An engine's camshaft(s) is/are responsible for the valve timing in the engine. Proper valve timing is critical for any four-stroke automotive engine to operate at maximum efficiency. When the valves open, how high the valves open (lift), and for how long they stay open (duration) all determine the performance characteristics of the engine. In the performance symphony, the camshaft is the conductor of valve events. It orchestrates which instruments play (intake or exhaust valves), when they play (opening and closing events) and how loud they play (valve lift). Whereas OEM conductors (cams) offer a classical sound, aftermarket cams can really make your engine rock.
The Band of Power
As mentioned earlier, the camshaft will determine an engine's character. The engine's character in terms of power production is often termed the "powerband." Where does the engine begin to make power? Where does the engine begin to fall off in power production? Is the power delivery flat and consistent or aggressive and peaky? These questions are answered in the description and understanding of the engine's powerband. Some powerbands are narrow, while other are deemed broad. Some are peaky, some are flat. An engine that makes appreciable power from only 6000 to 8000 rpm (a range of 2000 rpm) would be considered to have a narrow powerband. A comparable-sized engine that makes power from 3000 to 7000rpm (a range of 4000 rpm) might be considered to have a broad powerband. More so than any other internal components of the engine, the camshaft and its complimentary valvetrain components will establish the powerband of the engine.
The Ideal Cam
So how do you get the perfect cam? The cam that has tremendous low-end torque, a 10,000 rpm redline, an idle like mom's car and a powerband from idle to redline doesn't exist. Fortunately, an aftermarket performance camshaft that optimizes the rest of your performance combination to provide the performance that you desire probably does exist. Dollar for dollar there is a good chance that aftermarket cam(s) may be the best performance investment that you make.
Lift, Lobes and Symmetry
For every action, there is always a reaction. From a performance standpoint, the faster a valve opens and reaches full-lift, the better. Why? Horsepower is directly related to how much air and fuel can be stuffed into the cylinder. Air and fuel can't get into the cylinder unless the valves are open. Camshafts that quickly open the valves are said to have an aggressive lobe profile. Unfortunately, the laws of physics govern the maximum amount of possible valve acceleration or "aggressiveness." If the camshaft profile tries to accelerate the valve too fast, excessive wear or valvetrain problems can occur. When returning a valve toits seat, a camshaft once again cannot do this too fast or the valve slams into the valve seat (sometimes valves even bounce off the seat). Most modern cam designs optimize valve acceleration rates by designing camshafts with asymmetric lobes. This style of lobe lifts the valve faster than it lowers the valve. Quite simply, asymmetric lobe designs can be utilized to maximize the performance available while increasing the durability of the valvetrain.
Types of Engines
There are two basic styles of piston engines in production today, the overhead-valve engine (OHV) and the overhead-cam engine (OHC). Overhead valve engines rely on valve lifters, pushrods, rocker arms and a camshaft which rests in the engine's cylinder block. Examples of OHV engines include most of the domestic V8 and V6 engines manufactured over the last 50 years.
Knowing the Specs
Since we have already explored the basics of camshafts, we will now attempt to unlock the mysteries surrounding camshaft specifications. Since the camshaft(s) influence when an engine starts making power, when it stops producing power, maximum power output, fuel economy, idle quality, and engine efficiency, it is important to understand camshaft specifications. With this basic understanding, you will be better able to select the camshaft(s) that will keep you ahead of the competition.
Lift and Duration
The basic function of a camshaft is to open and close the engine's valves. On many applications, a single camshaft controls the opening and closing events of all the valves in an engine. Other applications may implement as many as four camshafts to control the valve events. Regardless of the number of cams, the rules that apply for single camshaft engines also apply to those with multiple camshafts. The most well-known camshaft specifications are lift and duration. Most manufacturers give specifications for lift at the valve, instead of at the camshaft. On some applications that don't use a
rocker assembly these two lifts may be the same. If you need to convert from lift at the camshaft lobe to lift at the valve, use the following equation.
Valve Lift = Lobe Lift x Cam Follower Ratio
Lift
Lift is nothing more than a measurement of the maximum distance the valve is opened. Assuming all other specifications remain the same, choosing a camshaft with more lift will increase the flow of air and fuel into an engine and the flow of exhaust out of an engine. As a result, more power can be made. In many cases, camshafts that have increased lifts over stock specifications and near stock duration will offer increased performance without making measurable sacrifices in "driveability". Everything has a limit and cylinder heads will generally reach a point where airflow no longer increases with an increase in valve lift. Before you order that mega-lift cam, please consider the following: when valve lift is dramatically increased, the possibility of valve to-piston contact, coil bind at the valve spring and valvetrain interference is also increased. To avoid bent valves, broken retainers and thin wallets, always use the necessary complimentary valvetrain components and check valve-to-piston clearance when recommended by the camshaft manufacturer.
Duration
Along with how high a valve is opened, how long it remains open also influences the performance of an engine. If you are trying to fill a glass at the sink, how much you open the faucet or valve, as well as how long you have that valve open will determine how much water fills the glass. How long you keep the faucet turned on is a simple measure of duration. The duration specification of a camshaft is measured in crankshaft degrees of which there are 720 in one complete four-stroke cycle. However, the problem with camshaft duration figures is that different manufacturers measure this duration at different valve lifts. The Brand-A manufacturer might measure duration as soon as the valve is lifted .015 of an inch off its seat until it returns to the same lift, while the Brand-C manufacturer might not start measuring until the valve is .050 inch off the seat. The result is that if we had both companies measure the same camshaft, Company-A might measure 306 degrees of duration (measuring at a minimum lift of .015"), while Company-C would measure 256 degrees of duration (measuring at .050"). In essence we have two completely different numbers for the same camshaft. Luckily, most camshaft manufacturers now provide duration figures at either a minimum lift of 1mm (Japan's industry standard measure) or a minimum lift of .050" (the traditional U.S. hot rod standard). When duration comparisons between two camshafts are being made, only compare the figures if the measurements have been taken at the same minimum lift.
Duration and Power
More lift translates into more power and torque across the powerband for most cases. In general, increased duration will shift the torque and horsepower peak to a higher rpm. All other specifications being the same, increasing duration yields more top-end and mid-range power while sacrificing low-end torque. As a result of the shifting of the powerband upstairs to higher rpms, a longer duration camshaft, when used with the appropriate valvetrain components, will also raise an engine's redline. One rule of thumb is that every 10 degree increase in duration (measured at 1mm or .050") will shift the torque peak and redline up by 500 rpm.
A Closer Look-Valve Timing
Believe it or not the explanation of lift and duration has been somewhat simplified. If we only look at lift and duration, we only know how high a valve is lifted and for how long. What lift and duration fail to tell us is when the valves are opened and closed. If we know that the complete four-stroke cycle contains 720 degrees of crankshaft rotation and the intake stroke (when the piston moves down the cylinder when the intake valve is open) makes up one-fourth of the cycle, we easily deduce that the theoretical duration of the intake cycle is 180 degrees (one-fourth of 720). If we could
instantaneously open the intake valve at TDC (the beginning of the intake stroke) and have the intake charge immediately start flowing into the cylinder until the piston was at BDC (the end of the intake stroke, 180 degrees later) where the intake valve would instantaneously slam shut, we might have an engine that would run well with only 180 degrees of intake duration.
Early Intake Valve Opening
In practice, there are many advantages to opening the intake valve early and closing it late. By initiating the opening the intake valve early, the intake valve has time to get to a lift where appreciable flow will begin. On a well-designed cylinder head teamed with a free-flowing exhaust, the pressure in the cylinder when the valve is opened early may be lower than atmospheric, so the intake charge actually gets sucked in (in practice, the exhaust valve is still open when the intake valve begins to open). The benefits of early intake valve opening are very rpm dependent. At low engine speeds, extremely early intake valve opening may cause exhaust gases to be sucked into the intake manifold causing erratic idle and other problems. At higher engine speeds, this same amount of early intake valve opening will have no adverse effects since the intake manifold is not operating under a vacuum condition.
Late Intake Valve Closing
Now that we understand why we need to open the intake valve early, let's take a close look at the closing of the intake valve. The reason we leave the intake valve open past Bottom Dead Center (BDC) is inertia: objects at rest tend to stay at rest, objects (or a mass of air in the case) in motion tend to stay in motion. Since we have an intake charge in motion we can experience additional filling of the cylinder while the piston dwells (or remains in place) at the bottom of its stroke at BDC. On engine with high rod length-to-stroke ratios, the piston may dwell around BDC for 20 degrees of crank rotation before the piston starts to move up the cylinder. During this time the flowing intake charge continues to fill the cylinder. If the intake valve closes too late, thepiston may pump some of the intake charge out of the cylinder through the intake valve and back into the intake manifold. This reverse flow is obviously undesirable. As you may have guessed, the optimum closing of the intake valve is also very rpm dependent.
Exhaust Valve Open Early
Since we have a good understanding of the intake side out the equation let's take a look at the exhaust side. The major difference in dealing with the exhaust side is that the average pressure in the cylinder is probably more than six times the average pressure during the intake cycle. This makes the task of releasing the exhaust gases easier than trying to get the intake charge into the cylinder. During the power stroke, the majority of horsepower is generated during the first 90 degrees or first half of this 180 degree cycle. This being the case, opening the exhaust valve early has little effect on killing power. In fact, power is usually increased since the residual pressure is released from the cylinder so the piston doesn't work as hard to push the remaining gases out when it begins its upward movement on the exhaust stroke.
Exhaust Valve Closing Late
Keeping the exhaust valve open after TDC can also have benefits. If the exhaust valve is kept open after TDC, the intake valve will also be open at the same time. When both intake and exhaust valves are open at the same time, it is termed valve overlap. The ideal amount of overlap depends on rpm. Higher rpms tolerate more overlap and the intake charge can be drawn into the cylinder due to the draft caused by the exhaust gases leaving the cylinder. When overlap gets excessive, exhaust gas can make its way into the intake manifold, diluting the intake charge. A diluted intake charge limits power production, so a careful balance must always be struck.
The Bottom Line
A camshaft may look simple, but its job is no easy task. Understanding the function, design and limitations of aftermarket cams will allow you to make educated decisions
about getting the right cam(s) for your car. Remember to rely on the experts. The wealth of knowledge that the major cam companies possess is incredible. While it is great to have an understanding of cams, there are enough self-proclaimed engineers in the world. Nine times out of ten, the specialist at the cam company will know more than you (that's his or her job). The value of your performance education is identifying the one out of ten instances that you may encounter. As always, remember to consider that the camshaft(s) are just one element of the performance combination. All of the parts in the combination need to work together to produce the maximum in power and reliability. Camshafts will only do there job effectively when complimented with the correct valvetrain component. Installation of the camshaft and complimentary valvetrain components must also be done correctly. Failure to do so will result in a loss of performance and the potential for component damage.
http://www.tprmag.com/issue/2/images/c_1.gif
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http://www.tprmag.com/issue/2/images/c_4.gif
Power Tech: Camshafts
Among all the components that make up an engine, the camshaft plays the most significant role in determining the behavior and character of the engine. As for the engine's behavior, most OEM camshafts offer idles that are smooth and polished. A radical aftermarket full-race camshaft may produce an idle that is rough and raw. As for character, one camshaft may regulate an engine to produce massive low-end torque, while a different camshaft in that same engine may soften up the power production at the low end while allowing the engine to pull strong up to redline. Understanding the function, design, and limitations of the camshaft will allow you to maximize your performance experience.
Function of the Camshaft
The four-stroke process that occurs in your car's engine is as follows: intake, compression, power, exhaust. While the crankshaft's position, crankshaft's stroke and rod length ultimately determine where the piston will be in the cylinder at any given degree of rotation, it's the camshaft that determines the position of the intake and exhaust valve during all four strokes. An engine's camshaft(s) is/are responsible for the valve timing in the engine. Proper valve timing is critical for any four-stroke automotive engine to operate at maximum efficiency. When the valves open, how high the valves open (lift), and for how long they stay open (duration) all determine the performance characteristics of the engine. In the performance symphony, the camshaft is the conductor of valve events. It orchestrates which instruments play (intake or exhaust valves), when they play (opening and closing events) and how loud they play (valve lift). Whereas OEM conductors (cams) offer a classical sound, aftermarket cams can really make your engine rock.
The Band of Power
As mentioned earlier, the camshaft will determine an engine's character. The engine's character in terms of power production is often termed the "powerband." Where does the engine begin to make power? Where does the engine begin to fall off in power production? Is the power delivery flat and consistent or aggressive and peaky? These questions are answered in the description and understanding of the engine's powerband. Some powerbands are narrow, while other are deemed broad. Some are peaky, some are flat. An engine that makes appreciable power from only 6000 to 8000 rpm (a range of 2000 rpm) would be considered to have a narrow powerband. A comparable-sized engine that makes power from 3000 to 7000rpm (a range of 4000 rpm) might be considered to have a broad powerband. More so than any other internal components of the engine, the camshaft and its complimentary valvetrain components will establish the powerband of the engine.
The Ideal Cam
So how do you get the perfect cam? The cam that has tremendous low-end torque, a 10,000 rpm redline, an idle like mom's car and a powerband from idle to redline doesn't exist. Fortunately, an aftermarket performance camshaft that optimizes the rest of your performance combination to provide the performance that you desire probably does exist. Dollar for dollar there is a good chance that aftermarket cam(s) may be the best performance investment that you make.
Lift, Lobes and Symmetry
For every action, there is always a reaction. From a performance standpoint, the faster a valve opens and reaches full-lift, the better. Why? Horsepower is directly related to how much air and fuel can be stuffed into the cylinder. Air and fuel can't get into the cylinder unless the valves are open. Camshafts that quickly open the valves are said to have an aggressive lobe profile. Unfortunately, the laws of physics govern the maximum amount of possible valve acceleration or "aggressiveness." If the camshaft profile tries to accelerate the valve too fast, excessive wear or valvetrain problems can occur. When returning a valve toits seat, a camshaft once again cannot do this too fast or the valve slams into the valve seat (sometimes valves even bounce off the seat). Most modern cam designs optimize valve acceleration rates by designing camshafts with asymmetric lobes. This style of lobe lifts the valve faster than it lowers the valve. Quite simply, asymmetric lobe designs can be utilized to maximize the performance available while increasing the durability of the valvetrain.
Types of Engines
There are two basic styles of piston engines in production today, the overhead-valve engine (OHV) and the overhead-cam engine (OHC). Overhead valve engines rely on valve lifters, pushrods, rocker arms and a camshaft which rests in the engine's cylinder block. Examples of OHV engines include most of the domestic V8 and V6 engines manufactured over the last 50 years.
Knowing the Specs
Since we have already explored the basics of camshafts, we will now attempt to unlock the mysteries surrounding camshaft specifications. Since the camshaft(s) influence when an engine starts making power, when it stops producing power, maximum power output, fuel economy, idle quality, and engine efficiency, it is important to understand camshaft specifications. With this basic understanding, you will be better able to select the camshaft(s) that will keep you ahead of the competition.
Lift and Duration
The basic function of a camshaft is to open and close the engine's valves. On many applications, a single camshaft controls the opening and closing events of all the valves in an engine. Other applications may implement as many as four camshafts to control the valve events. Regardless of the number of cams, the rules that apply for single camshaft engines also apply to those with multiple camshafts. The most well-known camshaft specifications are lift and duration. Most manufacturers give specifications for lift at the valve, instead of at the camshaft. On some applications that don't use a
rocker assembly these two lifts may be the same. If you need to convert from lift at the camshaft lobe to lift at the valve, use the following equation.
Valve Lift = Lobe Lift x Cam Follower Ratio
Lift
Lift is nothing more than a measurement of the maximum distance the valve is opened. Assuming all other specifications remain the same, choosing a camshaft with more lift will increase the flow of air and fuel into an engine and the flow of exhaust out of an engine. As a result, more power can be made. In many cases, camshafts that have increased lifts over stock specifications and near stock duration will offer increased performance without making measurable sacrifices in "driveability". Everything has a limit and cylinder heads will generally reach a point where airflow no longer increases with an increase in valve lift. Before you order that mega-lift cam, please consider the following: when valve lift is dramatically increased, the possibility of valve to-piston contact, coil bind at the valve spring and valvetrain interference is also increased. To avoid bent valves, broken retainers and thin wallets, always use the necessary complimentary valvetrain components and check valve-to-piston clearance when recommended by the camshaft manufacturer.
Duration
Along with how high a valve is opened, how long it remains open also influences the performance of an engine. If you are trying to fill a glass at the sink, how much you open the faucet or valve, as well as how long you have that valve open will determine how much water fills the glass. How long you keep the faucet turned on is a simple measure of duration. The duration specification of a camshaft is measured in crankshaft degrees of which there are 720 in one complete four-stroke cycle. However, the problem with camshaft duration figures is that different manufacturers measure this duration at different valve lifts. The Brand-A manufacturer might measure duration as soon as the valve is lifted .015 of an inch off its seat until it returns to the same lift, while the Brand-C manufacturer might not start measuring until the valve is .050 inch off the seat. The result is that if we had both companies measure the same camshaft, Company-A might measure 306 degrees of duration (measuring at a minimum lift of .015"), while Company-C would measure 256 degrees of duration (measuring at .050"). In essence we have two completely different numbers for the same camshaft. Luckily, most camshaft manufacturers now provide duration figures at either a minimum lift of 1mm (Japan's industry standard measure) or a minimum lift of .050" (the traditional U.S. hot rod standard). When duration comparisons between two camshafts are being made, only compare the figures if the measurements have been taken at the same minimum lift.
Duration and Power
More lift translates into more power and torque across the powerband for most cases. In general, increased duration will shift the torque and horsepower peak to a higher rpm. All other specifications being the same, increasing duration yields more top-end and mid-range power while sacrificing low-end torque. As a result of the shifting of the powerband upstairs to higher rpms, a longer duration camshaft, when used with the appropriate valvetrain components, will also raise an engine's redline. One rule of thumb is that every 10 degree increase in duration (measured at 1mm or .050") will shift the torque peak and redline up by 500 rpm.
A Closer Look-Valve Timing
Believe it or not the explanation of lift and duration has been somewhat simplified. If we only look at lift and duration, we only know how high a valve is lifted and for how long. What lift and duration fail to tell us is when the valves are opened and closed. If we know that the complete four-stroke cycle contains 720 degrees of crankshaft rotation and the intake stroke (when the piston moves down the cylinder when the intake valve is open) makes up one-fourth of the cycle, we easily deduce that the theoretical duration of the intake cycle is 180 degrees (one-fourth of 720). If we could
instantaneously open the intake valve at TDC (the beginning of the intake stroke) and have the intake charge immediately start flowing into the cylinder until the piston was at BDC (the end of the intake stroke, 180 degrees later) where the intake valve would instantaneously slam shut, we might have an engine that would run well with only 180 degrees of intake duration.
Early Intake Valve Opening
In practice, there are many advantages to opening the intake valve early and closing it late. By initiating the opening the intake valve early, the intake valve has time to get to a lift where appreciable flow will begin. On a well-designed cylinder head teamed with a free-flowing exhaust, the pressure in the cylinder when the valve is opened early may be lower than atmospheric, so the intake charge actually gets sucked in (in practice, the exhaust valve is still open when the intake valve begins to open). The benefits of early intake valve opening are very rpm dependent. At low engine speeds, extremely early intake valve opening may cause exhaust gases to be sucked into the intake manifold causing erratic idle and other problems. At higher engine speeds, this same amount of early intake valve opening will have no adverse effects since the intake manifold is not operating under a vacuum condition.
Late Intake Valve Closing
Now that we understand why we need to open the intake valve early, let's take a close look at the closing of the intake valve. The reason we leave the intake valve open past Bottom Dead Center (BDC) is inertia: objects at rest tend to stay at rest, objects (or a mass of air in the case) in motion tend to stay in motion. Since we have an intake charge in motion we can experience additional filling of the cylinder while the piston dwells (or remains in place) at the bottom of its stroke at BDC. On engine with high rod length-to-stroke ratios, the piston may dwell around BDC for 20 degrees of crank rotation before the piston starts to move up the cylinder. During this time the flowing intake charge continues to fill the cylinder. If the intake valve closes too late, thepiston may pump some of the intake charge out of the cylinder through the intake valve and back into the intake manifold. This reverse flow is obviously undesirable. As you may have guessed, the optimum closing of the intake valve is also very rpm dependent.
Exhaust Valve Open Early
Since we have a good understanding of the intake side out the equation let's take a look at the exhaust side. The major difference in dealing with the exhaust side is that the average pressure in the cylinder is probably more than six times the average pressure during the intake cycle. This makes the task of releasing the exhaust gases easier than trying to get the intake charge into the cylinder. During the power stroke, the majority of horsepower is generated during the first 90 degrees or first half of this 180 degree cycle. This being the case, opening the exhaust valve early has little effect on killing power. In fact, power is usually increased since the residual pressure is released from the cylinder so the piston doesn't work as hard to push the remaining gases out when it begins its upward movement on the exhaust stroke.
Exhaust Valve Closing Late
Keeping the exhaust valve open after TDC can also have benefits. If the exhaust valve is kept open after TDC, the intake valve will also be open at the same time. When both intake and exhaust valves are open at the same time, it is termed valve overlap. The ideal amount of overlap depends on rpm. Higher rpms tolerate more overlap and the intake charge can be drawn into the cylinder due to the draft caused by the exhaust gases leaving the cylinder. When overlap gets excessive, exhaust gas can make its way into the intake manifold, diluting the intake charge. A diluted intake charge limits power production, so a careful balance must always be struck.
The Bottom Line
A camshaft may look simple, but its job is no easy task. Understanding the function, design and limitations of aftermarket cams will allow you to make educated decisions
about getting the right cam(s) for your car. Remember to rely on the experts. The wealth of knowledge that the major cam companies possess is incredible. While it is great to have an understanding of cams, there are enough self-proclaimed engineers in the world. Nine times out of ten, the specialist at the cam company will know more than you (that's his or her job). The value of your performance education is identifying the one out of ten instances that you may encounter. As always, remember to consider that the camshaft(s) are just one element of the performance combination. All of the parts in the combination need to work together to produce the maximum in power and reliability. Camshafts will only do there job effectively when complimented with the correct valvetrain component. Installation of the camshaft and complimentary valvetrain components must also be done correctly. Failure to do so will result in a loss of performance and the potential for component damage.
http://www.tprmag.com/issue/2/images/c_1.gif
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