Camshaft Tips & Definitions

[1Bad62Pro/Street]

Just some helpfull info:


Camshaft Tips & Definitions
Life or Death Cam Knowledge
http://www.hotrod.com/techarticles/c...ons/index.html

What cam grind is right for your street machine? We’ve compiled some basic tips and terms that can prove helpful in the camshaft selection department.

Tip 1: A low compression-ratio powerplant will respond favorably to a camshaft that features relatively short duration figures, wide lobe centers, rapid valve opening rates, and a high lift number (comparatively). On the opposite side of the coin, an engine that features a high static compression ratio easily can use more duration and tighter lobe centers.

Tip 2: Virtually all of the major cam grinders (and more than a few oil companies) discourage the use of synthetic oils during engine break-in--particularly on engines with flat tappet (solid or hydraulic) camshafts. Instead, use a quality grade of naturally formulated oil for the break-in. You can safely use synthetics following the proper break-in period. Besides, synthetics are pricey, and you’d have to drain it out after the first 20 minutes or so anyway.

Tip 3: Valvespring damper failure is more common that we’d like to think (especially on high-lift, radical-profile camshafts). Occasionally, a damper will physically "unwind" and the lower portion of the assembly will work its way between two lower coils of the outer spring. Naturally, this stacks the spring into coil bind. One easy solution to this problem is to inspect the spring, inner spring, and damper carefully before installation. You might find that some valvesprings have added "flashing" on the spring ends (this is quite common on some dampers). If that’s the case with your spring(s), use a small die grinder and very carefully smooth over the burrs. Similarly, some dampers have very sharp edges on the "flats." The life of the damper can be improved by gently deburring and chamfering this section.

Tip 4: Before sliding a set of larger-than-stock ratio rockers inside your Chevy (as an example, adding 1.6:1 rockers in place of 1.5:1 rockers), carefully check for coil bind at the valvespring, especially in applications with stock or stock spec valvesprings. You need at least 0.40-inch clearance between the springs at maximum lift.

Tip 5: When installing an aftermarket, high lift camshaft with stamped-steel, stud-mounted rockers, be sure to check the rocker arm slot that allows the rocker to pivot at maximum lift. There should be approximately 0.60 inch of additional travel left in this slot when the valve is at maximum lift. At the same time, be sure that the rocker arm contacts only the valve tip, not the valvespring or retainer.

Tip 6: In the area of single- and dual-pattern camshafts, controversy seems to reign supreme. Proponents of the dual-pattern grind feel that a standard pushrod engine will breathe better on the intake side than it does on the exhaust side. In this scenario, the exhaust lift and duration figures are greater in order to compensate for the exhaust port’s inability to breathe. The single-pattern group points out that the exhaust is somewhat controlled by cylinder pressure. The piston movement helps to force the exhaust from the combustion chamber and, as a result, the intake port does not have any real advantage. This makes for a single-pattern camshaft that features identical intake and exhaust lobe profiles. Which is the better of the two designs? Both have merit. Your particular combination might respond properly with a dual-pattern cam grind while a slightly different Chevrolet might show promising results with a single-pattern grind.

Tip 7: Piston-to-valve clearance should always be checked when a high lift cam is installed in an engine. It should be pointed out that high-lift figures alone do not always contribute to piston-to-valve clearance problems. Overlap and rod length also can create problems.

Very seldom is a specific valve fully open when the piston reaches top dead center (TDC) in a wide-lobe-center, short-overlap camshaft application. As the lobe-center angle is decreased, the proximity of the valve face to the piston dome is increased. In a narrow-lobe-center, long-overlap application, the valve remains open for a longer period of time as the piston approaches TDC. This problem is magnified when a powerplant is fitted with "long" connecting rods. As the rod ratio number increases (due to the longer-than-stock connecting rod), the piston remains at TDC longer, which can contribute to piston to valve-clearance problems.

Tip 8: If you bend one or more pushrods for no apparent reason, there’s a very good chance the engine is experiencing some form of mechanical interference in the valvetrain. The places to look include the rocker arm-to-stud clearance, valvespring coil bind, interference between the retainer and the valve seal or retainer, and the valve guide. In addition, high engine rpm might be causing the valves to whack the pistons, which in turn bends the pushrods.

Tip 9: Never overlook the fact that pushrods of the wrong length can wreak havoc on the rocker arm geometry, adversely affect the amount of lift, and even contribute to valve guide wear in the engine. A number of factors can influence pushrod length and valvetrain geometry. These include a decked block, installation of a smaller base circle cam, lash caps, non-stock-length lifters, or custom-length valves, and alteration of the valve seat depth. If any of these items have been included in your engine, then the pushrods could be far too short. To measure the correct pushrod length, try a set of adjustable measuring pushrods.

Tip 10: When a stamped-steel rocker arm bites the dust on a Chevy V8, it’s usually an exhaust rocker. Why? Simply because the exhaust side runs hotter. But when it comes time to replace the rockers, swap a good used intake to the exhaust side and install a new rocker on the intake. That way, the new rocker won’t be killed before it’s "seasoned." It’s just cheap insurance.

Definition: Theoretical valve lift is the figure often published in cam manufacturers’ specification charts and is the most common term used to describe the lift of the cam. Theoretical valve lift does not take into account valve lash, valvetrain deflection underload, variables in rocker arm ratio, and so on. Think of theoretical valve lift as maximum valve lift under ideal conditions.

Definition: Net valve lift is the real-world number that your particular powerplant experiences with all variables taken into account. Items such as valve lash, valvetrain deflection, and rocker arm ratio variation are considered when this particular measurement is determined. It should be pointed out that it is virtually impossible for any camshaft grinder to print a true "net" figure on its specification card. The only viable method of determining actual net valve lift is by setting up a dial indicator on the nose of the rocker arm and measuring the lift while the powerplant is in an "operational" mode (but, of course, not running).

Definition: Lobe lift or camshaft lift is the term that describes the amount of lift the camshaft provides without any benefit of rocker arm ratio multiplication factors. For example, a small-block Chevrolet roller camshaft may have an advertised lobe lift of 0.350. If the engine makes use of a standard 1.50:1 ratio rocker arm, the final theoretical valve lift works out to 0.525 (0.350 X 1.5). In the event that the powerplant uses a 1.60:1 ratio rocker arm, the theoretical valve lift works out to 0.560-inch. Think of cam lift as the true amount the camshaft lifts the valve lifter in the respective lifter bore.

Definition: Advertised duration is the most common form of listing specific duration figures. It is measured in crankshaft degrees and basically expresses the length of time that a given valve is open. Unfortunately, this particular figure can be more optimistic than theoretical valve lift. A good portion of the discrepancy regarding advertised duration figures is due to the fact that many manufacturers tend to include the camshaft lobe clearance ramp in their duration figures. For example, a Chevrolet ZL1 camshaft has an advertised duration figure of 359 degrees on the exhaust side. Obviously, this is an extremely stout number and, when you give it some consideration, you can clearly see that the powerplant could hardly run with such a radical camshaft. This is where 0.050-inch duration figures come into play. Measured with the 0.050-inch method, the very same ZL1 grind features a duration figure of 273 degrees. That’s a significant difference.

Definition: The 0.050-inch duration figure is determined when the valve lifter has risen 0.050-inch off the camshaft base circle (opening side) and closed to within 0.050-inch (closing side) on the ramp. This particular duration figure is quite accurate for comparison purposes and in most areas is much closer to true duration than the advertised number. Airflow in the intake or exhaust port is minimal at low lift figures, especially when the clearance ramp numbers are included in the discussion. Since this airflow is almost nil in most situations, the camshaft manufacturers began using the 0.050-inch method to determine a universal number that could be used for camshaft comparison. The newer 0.050-inch number is more accurate and can, at least, be compared without worrying about variables such as ramp clearance.

Definition: Several camshaft grinders have begun to use the 0.020-inch duration figure in addition to the previously mentioned 0.050-inch number. It is primarily a seat duration figure and most often is used to determine valve timing at the seat. This figure is helpful when plotting a specific cam profile on graph paper and also can be of some assistance when comparing various camshaft profiles.

Definition: Overlap was once a very common figure but, much like advertised duration, it has fallen from favor as a comparison tool among many cam grinders. Basically, overlap is the number of degrees that the camshaft features with both the intake and exhaust valves open simultaneously. Overlap takes place at the beginning of the intake stroke and also at the end of the exhaust stroke.

Definition: Lobe center is the amount of camshaft degrees between the point of maximum lift on the intake lobe and the point of maximum lift on the exhaust side of a given pair of cam lobes. As an example, lobe center is calculated for cylinder number one only and does not deviate between number one and the other cylinders in the powerplant. To make a representative sketch of lobe center, draw a line between the very center of a camshaft intake lobe and then draw a similar line through the respective exhaust lobe for the same cylinder. The number of camshaft degrees between these two imaginary lines is the camshaft lobe center.

Also called lobe displacement angle (LDA), the lobe center has a definite bearing on how a particular camshaft will operate in a specific powerplant. If the lobe center of the camshaft is increased, the valve overlap will be decreased. The overlap decrease is created because the exhaust timing will occur earlier and the intake timing event will occur later in relation to crankshaft position. Conversely, if the lobe center or displacement angle is decreased, overlap increases. Note that lobe center cannot be changed once a camshaft has been ground.

Definition: Lobe centerline should not be confused with lobe center or lobe displacement angle. The term "lobe centerline" refers to an imaginary line drawn through each respective lobe but does not combine the separation angle between the intake and exhaust lobes in a given pairing. Lobe centerline can be altered by advancing or retarding a camshaft, while lobe center is a figure that cannot be altered since it is incorporated into the camshaft when it is designed and manufactured.

Definition: A symmetrical camshaft makes use of the same profile on the opening and closing side of a specific lobe. In other words, the opening side of an intake lobe features a shape that is exactly the same on the closing side of the lobe. This term should not be confused with single-pattern or dual-pattern camshafts (see below).

Definition: An asymmetrical camshaft features a lobe shape or profile that is different on the opening side than the closing side of the same lobe. For example, a camshaft could feature a very rapid valve opening profile, but when the valve is closing on the same lobe, the shape could be extremely smooth and gentle.

Definition: Single-pattern camshaft grinds feature identical intake and exhaust lobe configurations. This actually means that the valve timing is the same for both the intake lobe and the exhaust lobe. It should be pointed out that a camshaft can be asymmetrical in design yet still be a single-pattern grind. On the other hand, a camshaft can be symmetrical yet also be a single-pattern configuration.

Definition: Dual-pattern camshaft grinds make use of different profiles on the intake and exhaust lobes. This means that the exhaust lobe and the intake lobe are not identical in shape. A cam profile of this type could feature an asymmetrical lobe on the intake and a symmetrical lobe on the exhaust. It also could be symmetrical in both, asymmetrical in both, or any combination these types of profiles.

[ChiefRocka]

Good info !!!

I'm moving this to the engine side !!!

[1Bad62Pro/Street]

Camshaft Basics:
http://www.chevyhiperformance.com/te...s/viewall.html

[1Bad62Pro/Street]

Choosing the right cam.
http://www.hotrod.com/techarticles/1...t/viewall.html

[1Bad62Pro/Street]

How to Choose the Right Street Cam

Not so long ago, the bigger is better philosophy reigned supreme regarding camshafts. The result was overcammed engines that sounded great and could crank serious top-end power, but were not very streetable and couldn’t idle to save their lives.


But thanks to modern cam technology, you can come pretty darn close to the Holy Grail of street bumpsticks—cams that make high rpm power, have good low-end torque and drivability, decent vacuum for power brakes, and that loping idle we all love. Camshaft theory is a complex subject that can take a book-length article to explain. We’re going to concentrate on the basics you’ll need to know to choose a good street cam.


Lift and Duration
Lift and duration are the primary factors that determine a cam’s profile. Lift is the amount a cam lobe actually moves a valve off its seat, and is measured in fractions of an inch. Duration is the amount of time a cam keeps a valve off of its seat, measured in degrees of crank rotation.


Lift and duration combined determine total open valve area—the space available for air and fuel to flow into and out of the combustion chamber. The more valve area open to flow, the more power an engine can theoretically make. The trick is to “size” a cam to optimize valvetrain events for your particular engine combination and vehicle.


Cam Sizing
Virtually every cam maker uses duration to rate camshafts. When someone talks about a “big” cam, they are referring to cams with longer duration. This keeps the valves open longer, increasing midrange and top-end power at the expense of low-end torque. A shorter duration cam does just the opposite. Because it doesn’t keep the valves open as long, a smaller cam boosts low rpm torque and drivability. There are two ways to measure duration:


Advertised Duration is the figure you usually see in the cam ads and hear about at those late-night bench races. The problem with advertised duration is cam makers use various methods of measuring it, making it difficult to compare cams from different makers.


Duration at .050 measures duration at .050 inches of valve lift. Since all cam grinders use this measurement, it’s a much more accurate way to make a comparison. Two cams may be very close in advertised duration, for example, but make peak power at different rpms. Summit Racing uses duration at .050 ratings to help you better compare the wide variety of cams it carries.


Lobe Separation Angle
Lobe Separation Angle, or LSA, is the number of degrees that separate the peak lift points of the cam’s intake and exhaust lobes. LSA helps determine the cam’s behavior; you can take a given set of lift and duration figures, change the LSA, and get cams with vastly different characteristics. Generally, a cam with wider LSA (112-116 degrees) offers less overlap between intake and exhaust opening and closing events. That translates into a wider rpm range, better idle quality, and higher engine vacuum, but at the cost of less torque at low and midrange rpm. A cam with a narrow LSA (104-108 degrees) offers greater low and midrange torque production, but with a narrower operating range, a choppy idle, and less engine vacuum.


For the street, you want a cam that offers a compromise--decent idle quality, respectable vacuum for operating power brakes and such, and good overall power production. separation. Again, much depends on the overall engine combination and intended use, but as a general rule, cams with a 110 to 112 degree LSA offer good power and decent street manners.


Flat Tappet vs. Roller
Now that you have an idea of what lift and duration are, let’s muddy things up by comparing flat tappet and roller lifter cams. Flat tappet cams use a lifter with a slightly curved bottom that slides against the cam lobes. Virtually every V8 engine built before the late 1980s came with a flat tappet cam; they are reliable and relatively inexpensive. With literally hundreds of profiles to choose from, finding a good flat tappet cam for your street car is not difficult.


Roller cams are hardened steel cams that use lifters with a roller, or wheel, that rolls over the cam lobes. This design dramatically decreases valvetrain friction and wear, and allows designers to create profiles that offer more lift without increasing duration. That means a roller can make more midrange and top end power than a flat tappet cam of the same duration without sacrificing bottom end power. If you need proof that roller cams are better, ask the OEMs what they put in their engines nowadays.


Hydraulic or Solid?
Flat tappet and roller cams for overhead valve engines are available with hydraulic and mechanical lifters. Hydraulic lifters are self-adjusting; they use an oil-damped, spring-loaded plunger to help maintain valve lash (the distance between the valve stem and the rocker arm tip). Hydraulic lifter cams are quiet, require virtually no maintenance, and transmit less shock to the valvetrain. Their main drawback is a tendency to “pump-up” (overfill with oil) and cause the valves to float, or stay open too long, at high rpm. Valve float kills power, and can lead to engine damage if you keep your foot planted in the throttle.


Mechanical, or solid, lifters are not self-adjusting. They rely on a properly set up, adjustable valvetrain to maintain proper valve lash. Because solid lifter cams are less susceptible to valve float at higher rpms, they are ideal for more radical street and racing profiles. The price of running solid lifters is periodic adjustment of valve lash and increased valvetrain noise.


Overhead Cam Considerations
Overhead cam engines, like Ford’s 4.6 and 5.4 liter Modular V8s, follow the same rules regarding cam selection as overhead valve engines. The primary difference is how valve lift is determined. Overhead cam engines don’t use rocker arms, so there is no multiplication effect to increase valve lift (cam lift x rocker arm ratio = valve lift). Thus, cam lift and valve lift are the same.


The only way to increase lift with an overhead cam is to reduce the diameter of its base circle (the rounded bottom portion of the lobes). Changing the base circle increases valve lash as well, requiring the use of taller lash caps on the valve stems to maintain proper valve lash. This is a fairly involved process, which is a big reason why you’ll see many street cams for overhead cam engines with various duration figures but the same lift number.


Information, Please
Your sales rep or cam maker will need to know the following parameters to help you get the right cam grind for your particular vehicle and engine combination:


Vehicle Weight: You can run a bigger cam in a lightweight vehicle because less low-end torque is necessary to get it moving. Heavy vehicles need cams that emphasize low-end power.
Rear Axle Gear Ratio and Tire Size: If you have a bigger (numerically higher) axle gear ratio, you can use a bigger cam. Lower “economy” gears work better with a mild cam that makes power at low rpm. Tire height is important because it helps determine the final drive ratio.


Transmission Type: Cams for automatic transmissions have to work over a broader rpm range. Manual transmissions can tolerate a bigger cam biased to making peak power. The cam’s powerband should match torque converter stall speed or clutch “dump” rpm.
Engine Size and Compression: A cam’s profile is affected by displacement. Most cam descriptions for small block Chevys, for example, are based on 350 cubic inch engines. Put a cam in a 383 stroker and it will act like a milder grind. The more duration a cam has, the more compression is needed to maintain proper cylinder pressure at low rpm.


Airflow: Your cam needs to work within the airflow capabilities of the engine. The airflow characteristics of the cylinder heads (amount, intake/exhaust ratios, port work, etc.), induction system, and exhaust system are all factors.
Power Adders: Superchargers, turbos, and nitrous oxide require special cam profiles to take advantage of the extra power potential. In general, cams made for use with power adders are ground with wider lobe separation to take advantage of the extra cylinder pressure.


Rocker Arm Ratio: Going to a larger rocker arm ratio increases valve lift on overhead valve engines. The cam should be tailored to work with your specific ratio to avoid slapping valves into pistons or trashing valve springs.


Cam Comparison: 5.0L Mustang
Let’s compare two popular hydraulic roller cams for a 5.0L Fox-body Mustang that specs out as follows:
•3,400 pound vehicle weight, 5-speed, 3.73 rear axle gear
•306 cubic inch small block, 9.5:1 compression with EFI, aluminum heads, shorty headers, and cat-back exhaust


Cam One: Ford Racing X303
(Part Number FMS-M-6250-X303)
Advertised Duration: 286 degrees intake/exhaust
Duration at .050: 224 degrees intake/exhaust
Valve Lift (with 1.6 rocker): .542 inches intake/exhaust
Lobe Separation: 110 degrees
Powerband: 2,500-6,200 rpm


Cam Two: Comp Cams Xtreme Energy OE Roller 35-514-8
(Part Number CCA-35-514-8)
Advertised Duration: 266 degrees intake, 274 degrees exhaust
Duration at .050: 216 degrees intake/224 degrees exhaust
Valve Lift (with 1.6 rocker): .545 inches intake/.555 inches exhaust
Lobe Separation: 112 degrees
Powerband: 1,600-5,600 rpm


If you look at just advertised duration, the Comp grind looks less aggressive than the Ford Racing cam. But when you check duration at .050, both cams are virtually the same. This is an example of why duration at .050 is a much better comparison method.


Where our cams diverge is in lift and lobe separation. The Comp Xtreme Energy grind offers far more lift and a relatively wide 112 degree lobe separation, so it makes good power across the rpm band. The extra lift and duration on the exhaust side helps improve the small block Ford’s poor exhaust breathing. Comp recommends the cam for cars with 3.27-3.73 gears, Mass Air systems, and mild modifications like a larger throttle body, headers, and free-flowing exhaust. Either a five-speed or an AOD automatic with a mild stall converter would work with this cam.


The Ford Racing X303 has slightly lower lift figures, but is ground with a narrower 110 degree lobe separation. That makes the cam more biased toward high rpm power production. In fact, peak horsepower rpm comes at a rather lofty 6,500 rpm, almost 1,000 rpm higher than the Xtreme Energy cam. Ford Racing says the X303 should be used with a five-speed manual transmission.


We hope this little primer gave you the knowledge you need to choose the right cam for your street ride. If you want to get a PhD in camshaft-ology, companies like Crane, Comp Cams, Iskenderian , and Lunati have loads of information on their websites to help you become Dr. Bumpstick. Happy cam shopping!
http://www.summitracing.com/expertad...ht-Street-Cam/



Additional Sources
Comp Cams: www.compcams.com
Crane Cams: www.cranecams.com
Ed Iskenderian Cam Co.: www.iskycams.com
Lunati Cams: www.lunaticamshafts.com

[1Bad62Pro/Street]

Camshafts 101: A Glossary of Camshaft and Valvetrain Terms
If the rotating assembly is the heart and soul of your engine, then the camshaft is the brain. The camshaft controls the movement of the entire valvetrain, telling the valves when to open and close and allowing your engine to breathe properly.


Like the human brain, the camshaft is a highly complex entity and even commands its own vocabulary. That’s why we’ve teamed up with some of our camshaft manufacturers to create a basic glossary of cam and valvetrain terms. Armed with this guide, you can understand the sometimes-complex language of cam manufacturers and translate it into increased performance by choosing the right camshaft.


ADVANCE:
In reference to engine timing, advance occurs when combustion begins before the piston reaches Top Dead Center (TDC). In reference to camshaft timing, advance allows the intake and/or exhaust valves to open and close earlier in the engine cycle.


AREA UNDER THE CURVE:
Describes what the valve lift cycle would look like if plotted on a graph. A graph depicting “area under the curve” usually includes the crank degrees running horizontally and valve lift (in thousandths of an inch) running vertically. The more quickly the valve opens and remains open, the greater the area under the curve.


ASYMMETRICAL:
A type of camshaft lobe profile where the opening and closing ramps (see definitions below) are not identical. Some camshafts are designed this way to achieve an opening ramp profile that has a high velocity and a closing ramp profile that has a slower velocity.


BASE CIRCLE:
The base circle, also known as the heel, is the lowest point of the camshaft lobe and is the section of the cam lobe where the valve is in the closed position.


CAM BUTTON:
Located in the center of the timing gear, the cam button contacts the back of the timing cover and reduces camshaft endplay (the ability of the camshaft to move back and forth).


CAM DEGREEING:
The process of measuring the exact degree position of the camshaft relative to the combustion cycle. This process allows cam timing to be adjusted to match the performance characteristics of the engine.


CAM PROFILE:
The actual shape of the camshaft lobes.


CLOSING RAMP:
The portion of the camshaft lobe from the nose (highest lift point on the cam lobe) to the closed valve position.


COIL BIND:
The point at which a valve spring is no longer able to be compressed.


DUAL PATTERN:
A camshaft design in which the intake lobe profile differs from the exhaust lobe profile.


DURATION:
Camshaft duration is the period of time, measured in degrees of crankshaft rotation, that a valve is open. “Advertised duration” measures duration from the point where the cam manufacturer believes the lobe starts raising the lifter. This is called the checking height and it varies from manufacturer to manufacturer. The best way to measure duration is “duration at .050” because it gives every cam the same standardized starting point for measuring duration. “Duration at .050” lift is the deciding factor to what the engine’s basic rpm range will be. Lower duration cams produce the power in the lower rpm range. Larger duration cams operate at higher rpm, but lose bottom end power.


ENDPLAY:
The movement of the camshaft forward and backward within the camshaft galley. Setting the proper amount of endplay is important to avoid excessive valvetrain wear and timing chain failure and ensure proper lifter positioning.


ENGINE VACUUM:
The amount of vacuum generated by the engine within the intake manifold during combustion. Camshaft duration directly affects the amount of engine vacuum created.


FLAT TAPPET CAMSHAFT:
A camshaft that uses a lifter with a slightly curved bottom that slides against the cam lobes. Virtually every V8 engine built before the late 1980s used this type of camshaft.


HYDRAULIC LIFTERS:
Designed for use with flat tappet or roller cams, hydraulic lifters use an oil-damped, spring loaded plunger to help maintain valve lash. Ideal for street performance applications, this type of lifter offers quiet operation and requires virtually no maintenance.


INTAKE CENTERLINE:
The midpoint of the intake lobe.


INSTALLED HEIGHT:
Measured from spring seat to the top of the retainer, this is the overall height of a valve spring once installed.


JOURNAL DIAMETER:
The cross sectional diameter of the cam bearing journal.


LIFT:
The distance the valve travels to its maximum open position measured in fractions of an inch. The amount of lift you have and the speed at which the valve moves is a key factor in determining how much torque the engine will produce.


LIFTER PRELOAD:
The initial pressure applied to the lifter, most often through the rocker arm system.


LOBE SEPARATION ANGLE:
The distance in cam degrees between the maximum lift point on the intake lobe and the maximum lift point on the exhaust lobe. This measurement provides a clue as to how the intake and exhaust lobes work in conjunction with one another to establish the engine’s breathing pattern. Generally speaking, a wide lobe separation angle broadens the powerband, and narrow lobe separation creates more low-rpm torque.


MECHANICAL LIFTERS:
Lifters that have solid construction (no hydraulics). Mechanical lifters are ideal for high rpm applications but require an adjustable valvetrain to maintain proper valve lash.


NOSE:
The highest maximum lift point on the camshaft lobe. It is where valves are kept open for as long as possible before making the transition to the closing ramp.



OPENING RAMP:
Responsible for opening the valve to its maximum lift point, this section of the camshaft lobe is located between the base circle and the lobe peak, or nose.




OPEN PRESSURE:
Spring pressure created when the valve is open. Open pressure is essential to creating proper valve control.


OVERLAP:
The amount of time that both the intake and exhaust valves are open at the same time and the piston is at Top Dead Center (TDC).


O.D and I.D.:
Generally relates to valve springs and refers to their outside diameter and inside diameter measurements.


PISTON-TO-VALVE CLEARANCE:
The clearance between the valve and the piston when the two are at their closest point.


RAMP SPEED:
The angle of the camshaft lobe and how it relates to the opening and closing speed of the valves. The more aggressive the lobe ramp, the faster the valve opens and closes. The faster the valve opens and closes, the faster the ramp speed.


RETARD:
In reference to engine timing, retard occurs when combustion begins after the piston reaches Top Dead Center (TDC). In reference to camshaft timing, retard allows the intake and/or exhaust valves to open and close later in the engine cycle.


ROCKER ARM RATIO:
The differential between the pushrod and valve stem side of the rocker axis point, expressed as a ratio.


ROLLER CAMSHAFT:
A camshaft that utilizes a lifter with a roller, or wheel, that rolls over the cam lobes. This design reduces valvetrain friction and wear.


SEAT PRESSURE:
Measured in pounds per square inch, seat pressure is the pressure exerted on the spring seat.


SHIM:
A thin flat disc in varying thicknesses used to adjust (compress) the valve spring’s installed height.


SINGLE PATTERN CAMSHAFT:
A camshaft that utilizes the same specifications (lift and duration) on the intake and exhaust sides, creating identical lobe profiles.


SYMMETRICAL:
Refers to the profiles of the opening and closing ramps of a camshaft lobe and denotes that the ramps are identical.


TOP DEAD CENTER (TDC):
The highest point achieved by the piston travel within the cylinder bore.


VALVE LASH:
A measurement taken between the tip of the valve stem and rocker arm tip. Valve lash is always measured with the lifter positioned off the lobe of the cam.


VALVE MARGIN:
The distance from the face of the valve straight up the side of the valve to the bottom edge of the valve seat.

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