Have you ever wondered about the specifications stated on the outside of a camshaft box, what they mean, or how to take advantage of them? Valve lift is often the topic that opens cam discussions. Fortunately, it’s meaning is fairly straightforward. Camshaft makers use valve lift to induce as much airflow through the engine as possible. Efficient cylinder heads on a 632 big-block Chevrolet, for example, will provide impressive flow characteristics up to 1.000-inch of valve lift—while most Mountain Motor Pro Stock teams seek valve lift well in excess of this—and increase it further by employing 2:1 rockers.
“But most Sportsman guys with a 632,” explains Jeff Sams of Lunati, “are reluctant to select a camshaft with such large valve lift because it is so destructive to parts.” Sams, a Pro Stock Mountain Motor owner, builder and tuner, bridles, “So, Lunati devised a happy medium using an .810-inch lift.” The .810 camshaft can operate with the normal 1.70/1.70:1 rocker ratio or with increased rocker ratios of 1:85/1.75:1 or even on 1:85/1:85:1. Sams continues, “Normally, it’s desirable to favor the inlet valve with more lift because it responds better. The exhaust valve, in contrast, doesn’t benefit as much from lift—it responds more to duration.”
Still, valve lift needs to be considered carefully. Let us assume we are tuning a drag race 632-ci big-block Chevrolet engine and our race camshaft provides a maximum inlet valve lift of .810-inch and maximum exhaust valve lift of .778-inch. This means the incoming charge has a maximum opening around the inlet valves of .810-inch and the exhausted gases flow through a maximum valve opening of .778-inch as they escape into the pipe.
Accounting for valve lash and a little pushrod deflection, valve lift is usually reduced by around .030-inch. Perhaps the first question should be whether or not the amount of valve lift specified on the cam box is sufficient to support the torque and rpm of my engine? In addition, the camshaft lobes, via the pushrods and rockers, open the valves, but it is the springs that close them.
Big-block and Pro Stock Mountain Motor exponent Chuck Lawrence of Jon Kaase Racing Engines suggests, “Knowing the amount of valve lift conveys many important spring requirements. The valve lift figure, for example, determines how tall the spring needs to be to enable it to open fully without becoming coil bound.
“It is also important to ensure the bottom of the spring retainer does not make contact with the valve stem seal or the valve guide. The key to selecting optimum spring pressures is to find the lightest pressure that will close the valve, keep it closed, and not allow it to chatter on the valve seat. Some of Kaase’s racing big-blocks might function with springs providing 500 psi of seat pressure (the pressure exerted on the spring when the valve is closed) and 1,200 psi of open pressure. Over time valve springs lose their strength so to avoid seat chatter we might change them when their seat pressure deteriorates to around 300 psi.”
Lobe Lift
The next term expressed on the camshaft box is lobe lift. Lobe lift and rocker ratio are a function of valve lift. Consider a lobe lift dimension of .476-inch and multiply it by 1.7 (the common rocker ratio of a big-block Chevrolet) and the resulting valve lift will compute to around .810-inch.
Increasingly, camshaft cores and journals have become larger in diameter to contribute greater stiffness to the valve train and also to accommodate larger lobes. Large lobes cannot be fitted in the engine block’s camshaft tunnel unless the journal diameters are even larger. In today’s racing engines, bearing journal diameters of 65mm are not uncommon, while professional teams are using nine-bearing 70mm camshafts in engine blocks that permit their burly proportions. Sufficient working clearance is usually their chief impediment. At these levels of competition, where the production of maximum power is the only objective, engine builders will try to find an engine block that will accept the largest cam bearing diameter, and therefore, the largest cam lobe. In addition, they will increase their rocker ratio to around 2:1.
But the greater the lobe lifts, the greater distance the lifter travels within its bore, and as a result, the greater it is affected by wear and tear. In an attempt to reduce lifter wear some race engine builders select a camshaft with moderate lobe lift and increase the rocker ratio to gain extra valve lift. Either way the spring is exposed to hard labor and needs replacing when its strength begins to fade.
Lobe lift is calculated by measuring the lobe’s overall dimension (toe-to-heel) and subtracting its base circle dimension. For example, the toe-to-heel dimension of the big-block cam specs displayed on the box is 1.462 inches and its base circle .986-inch. Its lobe lift, therefore, will be calculated as .476-inch.
Adv. Dur.
The term “Adv. Dur.” denotes advertised duration. Though not so commonly used as other references, it indicates seat-to-seat duration. Lunati measures its advertised duration of hydraulic camshafts at .006-inch. (valve off its seat), and often refers to it as duration at .006-inch. The advertised duration of solid camshafts is measured at .020-inch. in order to compensate for valve lash.
Dur. @ .050-Inch
In contrast, the term “Dur. @ .050-inch” tappet lift is very common. Reducing the duration reduces the overlap, which in turn increases cylinder pressure.
Aided by a degree wheel and with a dial gauge indicator on the lifter, Jeff Sams explains how it is measured: “First you rotate the engine clockwise until your lifter is raised .050-inch. To eliminate the slack in the chain, turn the wheel counterclockwise by .100-inch and then clockwise .050-inch. Mark the number on your degree wheel and continue to rotate it clockwise, through its cycle, until the lifter falls back to .050in.”
Valve Lash
Valve lash is the mechanical clearance in valve trains with solid lifters. It is measured between the valve stem tip and the underside of the rocker arm. Valve lash is intended to provide the greatest amount of valve opening as the lifter travels over the high point—the nose—of the camshaft lobe, while still ensuring that the valve is tightly closed as the lifter travels over the low segment of the camshaft lobe, the base circle. Though some racers will attempt to gain a slight power advantage running looser lash settings, camshafts with aggressive lobes and excessive lash clearance risk damage to the valve stem tips, pushrod ends and lifters. It is also prudent to inspect the geometrical arc of the rocker arm as it sweeps across the valve tip.
Center Line
The term “center line” refers to the point of peak lift of a camshaft lobe in relation to top dead center of the piston as measured in crank degrees. This can be changed by “degreeing” the cam. In this case, when the cam is degreed by advancing it 4 degrees, its center line will be 110 degrees. This means that the maximum lift of the Number One intake valve will occur when the Number One piston is positioned 110 crank degrees after top dead center.
To check the center line of the Number One intake lobe using a degree wheel, locate true top dead center of the Number One piston and set your pointer to zero on the degree wheel. Then place a solid lifter on the Number One intake lobe and position a dial gauge indicator on the lifter. Turn the engine clockwise until the lifter reaches peak lift and set the dial gauge to zero. Then turn the engine counter clockwise until the indicator falls .100-inch. Next, turn the engine clockwise until the dial gauge reads .050-inch and note the degree wheel reading. Continue to turn the engine clockwise (over peak) until the indicator reaches .050-inch after maximum lift and again note the degree wheel reading. Add these numbers together and divide them by 2. The resulting number represents the intake centerline.
Timing at .050-Inch Tappet Lift
The final rows of data on the box display valve timing data at .050-inch tappet lift. They are as follows: The inlet valve opens at 35 degrees before top dead center and closes 75 degrees after bottom dead center; the exhaust valve opens 90 degrees before bottom dead center and closes 34 degrees after top dead center.
Spintron
The best tool ever devised for testing valve train components is the Spintron. It identifies and records crucial valve train characteristics such as valve bounce, tappet lofting, spring harmonics, pushrod deflection and more. Employed by all top teams where engine power is at a premium, the Spintron will check valve train performance from 500 to 20,000 rpm. It works in tandem with the dynamometer, and having one, or at least access to one, provides the race engine builder with a significant advantage.
Text and Photos by Sam Logan
Source: Drag Racer
“But most Sportsman guys with a 632,” explains Jeff Sams of Lunati, “are reluctant to select a camshaft with such large valve lift because it is so destructive to parts.” Sams, a Pro Stock Mountain Motor owner, builder and tuner, bridles, “So, Lunati devised a happy medium using an .810-inch lift.” The .810 camshaft can operate with the normal 1.70/1.70:1 rocker ratio or with increased rocker ratios of 1:85/1.75:1 or even on 1:85/1:85:1. Sams continues, “Normally, it’s desirable to favor the inlet valve with more lift because it responds better. The exhaust valve, in contrast, doesn’t benefit as much from lift—it responds more to duration.”
Still, valve lift needs to be considered carefully. Let us assume we are tuning a drag race 632-ci big-block Chevrolet engine and our race camshaft provides a maximum inlet valve lift of .810-inch and maximum exhaust valve lift of .778-inch. This means the incoming charge has a maximum opening around the inlet valves of .810-inch and the exhausted gases flow through a maximum valve opening of .778-inch as they escape into the pipe.
Accounting for valve lash and a little pushrod deflection, valve lift is usually reduced by around .030-inch. Perhaps the first question should be whether or not the amount of valve lift specified on the cam box is sufficient to support the torque and rpm of my engine? In addition, the camshaft lobes, via the pushrods and rockers, open the valves, but it is the springs that close them.
Big-block and Pro Stock Mountain Motor exponent Chuck Lawrence of Jon Kaase Racing Engines suggests, “Knowing the amount of valve lift conveys many important spring requirements. The valve lift figure, for example, determines how tall the spring needs to be to enable it to open fully without becoming coil bound.
“It is also important to ensure the bottom of the spring retainer does not make contact with the valve stem seal or the valve guide. The key to selecting optimum spring pressures is to find the lightest pressure that will close the valve, keep it closed, and not allow it to chatter on the valve seat. Some of Kaase’s racing big-blocks might function with springs providing 500 psi of seat pressure (the pressure exerted on the spring when the valve is closed) and 1,200 psi of open pressure. Over time valve springs lose their strength so to avoid seat chatter we might change them when their seat pressure deteriorates to around 300 psi.”
Lobe Lift
The next term expressed on the camshaft box is lobe lift. Lobe lift and rocker ratio are a function of valve lift. Consider a lobe lift dimension of .476-inch and multiply it by 1.7 (the common rocker ratio of a big-block Chevrolet) and the resulting valve lift will compute to around .810-inch.
Increasingly, camshaft cores and journals have become larger in diameter to contribute greater stiffness to the valve train and also to accommodate larger lobes. Large lobes cannot be fitted in the engine block’s camshaft tunnel unless the journal diameters are even larger. In today’s racing engines, bearing journal diameters of 65mm are not uncommon, while professional teams are using nine-bearing 70mm camshafts in engine blocks that permit their burly proportions. Sufficient working clearance is usually their chief impediment. At these levels of competition, where the production of maximum power is the only objective, engine builders will try to find an engine block that will accept the largest cam bearing diameter, and therefore, the largest cam lobe. In addition, they will increase their rocker ratio to around 2:1.
But the greater the lobe lifts, the greater distance the lifter travels within its bore, and as a result, the greater it is affected by wear and tear. In an attempt to reduce lifter wear some race engine builders select a camshaft with moderate lobe lift and increase the rocker ratio to gain extra valve lift. Either way the spring is exposed to hard labor and needs replacing when its strength begins to fade.
Lobe lift is calculated by measuring the lobe’s overall dimension (toe-to-heel) and subtracting its base circle dimension. For example, the toe-to-heel dimension of the big-block cam specs displayed on the box is 1.462 inches and its base circle .986-inch. Its lobe lift, therefore, will be calculated as .476-inch.
Adv. Dur.
The term “Adv. Dur.” denotes advertised duration. Though not so commonly used as other references, it indicates seat-to-seat duration. Lunati measures its advertised duration of hydraulic camshafts at .006-inch. (valve off its seat), and often refers to it as duration at .006-inch. The advertised duration of solid camshafts is measured at .020-inch. in order to compensate for valve lash.
Dur. @ .050-Inch
In contrast, the term “Dur. @ .050-inch” tappet lift is very common. Reducing the duration reduces the overlap, which in turn increases cylinder pressure.
Aided by a degree wheel and with a dial gauge indicator on the lifter, Jeff Sams explains how it is measured: “First you rotate the engine clockwise until your lifter is raised .050-inch. To eliminate the slack in the chain, turn the wheel counterclockwise by .100-inch and then clockwise .050-inch. Mark the number on your degree wheel and continue to rotate it clockwise, through its cycle, until the lifter falls back to .050in.”
Valve Lash
Valve lash is the mechanical clearance in valve trains with solid lifters. It is measured between the valve stem tip and the underside of the rocker arm. Valve lash is intended to provide the greatest amount of valve opening as the lifter travels over the high point—the nose—of the camshaft lobe, while still ensuring that the valve is tightly closed as the lifter travels over the low segment of the camshaft lobe, the base circle. Though some racers will attempt to gain a slight power advantage running looser lash settings, camshafts with aggressive lobes and excessive lash clearance risk damage to the valve stem tips, pushrod ends and lifters. It is also prudent to inspect the geometrical arc of the rocker arm as it sweeps across the valve tip.
Center Line
The term “center line” refers to the point of peak lift of a camshaft lobe in relation to top dead center of the piston as measured in crank degrees. This can be changed by “degreeing” the cam. In this case, when the cam is degreed by advancing it 4 degrees, its center line will be 110 degrees. This means that the maximum lift of the Number One intake valve will occur when the Number One piston is positioned 110 crank degrees after top dead center.
To check the center line of the Number One intake lobe using a degree wheel, locate true top dead center of the Number One piston and set your pointer to zero on the degree wheel. Then place a solid lifter on the Number One intake lobe and position a dial gauge indicator on the lifter. Turn the engine clockwise until the lifter reaches peak lift and set the dial gauge to zero. Then turn the engine counter clockwise until the indicator falls .100-inch. Next, turn the engine clockwise until the dial gauge reads .050-inch and note the degree wheel reading. Continue to turn the engine clockwise (over peak) until the indicator reaches .050-inch after maximum lift and again note the degree wheel reading. Add these numbers together and divide them by 2. The resulting number represents the intake centerline.
Timing at .050-Inch Tappet Lift
The final rows of data on the box display valve timing data at .050-inch tappet lift. They are as follows: The inlet valve opens at 35 degrees before top dead center and closes 75 degrees after bottom dead center; the exhaust valve opens 90 degrees before bottom dead center and closes 34 degrees after top dead center.
Spintron
The best tool ever devised for testing valve train components is the Spintron. It identifies and records crucial valve train characteristics such as valve bounce, tappet lofting, spring harmonics, pushrod deflection and more. Employed by all top teams where engine power is at a premium, the Spintron will check valve train performance from 500 to 20,000 rpm. It works in tandem with the dynamometer, and having one, or at least access to one, provides the race engine builder with a significant advantage.
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| DR-1105-CAM-LEAD |
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| The etchings on Lunati camshafts typically denote the type of cam (Voodoo); the part number (60512), which determines the grind profile; the day on which it was made (258th day of 2010); and the lobe separation angle (113 degrees). |
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| Checking the straightness of the five journals of a 5160 induction-hardened camshaft. The center journal is the one first checked for straightness. It is permitted a tolerance no greater than .001-inch. If it meets tolerance requirements, usually the remaining journals will also pass the straightness checks. The blackness between the lobes usually indicates the induction-hardening process. In contrast, copper coating indicates carburizing, an Austempering process that also contributes a case hardening depth of around.130-inch. |
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| A quick zap with the air hammer is used for straightening. The fuel pump lobe at the front and the distributor drive at the rear denote this cam will be used in a Chevrolet. |
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| Lunati uses a Landis grinding machine to produce all of its premium and high-volume camshafts. The carriage securing the camshaft moves right to left and the grinding wheel moves fore and aft. Here the first three lobes are ground and the machine is stopped to check the lobes for toe-to-heal accuracy. |
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| Simply program the part number into the Landis and 16 to 18 minutes later a perfect camshaft is born. After grinding the camshaft it is returned for further straightness checks. |
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| Manual grinders are used to produce one-off and low-volume camshafts. This process is performed in two stages: roughing (as depicted here) and finishing. |
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| Grinding speeds—the first essential of a quality camshaft maker. A key element in the finish-grinding process of a high-quality competition camshaft concerns grinding speed. If the speed is kept low, the quality of the grind will be high. If production numbers are allowed to trump quality and the grinding speeds are increased, the quality will be lower. |
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| Measuring the toe-to-heal dimension to ensure the lobe has been ground to the correct size. The first check, interestingly, is to ensure the lobe is smaller than the journal, thereby ensuring the cam will fit the block! |
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| With cam profiles already programmed in the inspection machine, it runs the ball along the lobes, comparing its findings with the design data. Its duties include measurements of taper, base circle, base circle run-out, toe-to-heal and lobe separation angles. In contrast, the essential attribute of the flat tappet cam lobe is, indeed, the taper on which the lifter rotates. |
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| Polishing the journals is one of the final operations. |
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| Don’t forget to read the spec card. It contains valuable details about the camshaft’s specifications as well as information about break-in lube, valve springs and how to find the center of the intake lobe. |
Text and Photos by Sam Logan
Source: Drag Racer
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