There is much to be edited and added, so I am not finished. I hope this helps you guys out as I build it up
If corrections need to be made, feel free to let me know.
Post One will include terms and valve timing explained along with extra links.
Post Two will be continued and include common 5.0L camshaft specifications.
After reading much of the following, you will quickly realize that a camshaft is the brains of an engine and how IMPORTANT it is to get a camshaft to match your goals and engine combination. This is where custom cam grinders shine
Contact either of the following to find out more, and how it is money well spent.
Ed Curtis ([email protected]) @ www.flowtechinduction.com
Buddy Rawls ([email protected]) @ http://www.wighat.com/fcr3/index.html
Camshaft Term Glossary
ABDC:
Degrees after bottom dead center.
ATDC:
Degrees after top dead center.
AREA UNDER THE CAM LIFT CURVE:
The area under the bell shaped curve with lift on the vertical axis and degrees of rotation on the horizontal axis. The greater the area under the lift curve, the greater is the lift and/or duration at some point on the camshaft profile.
BASE CIRCLE:
The concentric or round portion of the cam lobe where the valve lash adjustments must be made. (Also known as the heel.)
BBDC:
Degrees before bottom dead center.
BTDC:
Degrees before top dead center.
CAM FOLLOWER/TAPPET:
Usually a flat faced or roller companion to the camshaft that transfers the action of the camshaft to the rest of the valve train by sliding or rolling on the cam lobe surface.
CAM LIFT:
This is the maximum distance that the cam pushes the follower when the valve is open. This is different from valve lift. See "GROSS VALVE LIFT."
CAM MASTER:
After the design of the cam is computed, it is transferred to a precision template or master. The master is then installed in the cam grinding machine to generate the shape of the lobes of the production cam.
CAM PROFILE:
The actual shape of the cam lobe.
CAMSHAFT:
A shaft containing many cams that covert rotary motion to reciprocating (lifting) motion. For every 2 revolutions of the crankshaft, the camshaft rotates 1 revolution. The lobes on the camshaft actuate the valve train in relation to the piston movement in an internal combustion engine. The camshaft determines when the valves open and close how long they stay open and how far they open.
CARBURIZING:
Gas carburizing is a method to heat-treat steel camshaft billets. In this method, the camshaft is placed in a carbon gas atmosphere furnace and heated to the proper temperature. When the shaft has absorbed the proper amount of carbon, it is removed from the furnace and quenched to the proper temper.
CAST BILLET:
A term used to describe a camshaft that is made from a casting. The material for the casting is a special grade of iron alloy called "Proferal." GLOSSARY OF CAMSHAFT TERMS (CONTINUED)
CHEATER CAMS:
See "Improved Stock Cams".
CHILLED IRON LIFTER:
A cam follower made from high quality iron alloy that is heat treated by pouring the molten iron into a honeycomb mold with a chilled steel plate at the bottom to heat treat the face of the lifter. It is compatible with steel and hardface overlay cams only.
CLEARANCE RAMPS:
The portion of the cam lobe adjacent to the base circle that lifts at a constant slow speed. It's purpose, in theory, is to compensate for small deflections and take up the slack in the valve train created by the valve lash. The opening ramp takes up all clearances in the valve train and causes the valve to be on the verge of opening. The closing ramp begins when the valve touches the valve seat and ends when the tappet returns to the base circle. Ramp designs have a tremendous effect on power output and valve train reliability.
COIL BIND:
A valve spring that has been compressed to the point where the coils are stacked solid and there is no space left between the coils. The valve cannot open any further at when this happens.
CONCENTRIC:
Running true or having the same center. In camshaft terminology, the cam bearings and lobes are concentric to each other when the cam is straight and there is .001" or less runout between all the cam lobes and bearings.
DURATION AT .050":
The amount of time measured in degrees of crankshaft rotation from when the valve is open .050" far until it is .050" from closing.
FLAME HARDENING:
A heat treating process whereby a camshaft is exposed to an open flame and then quenched (cooled in oil).
FLANKS:
The sides of the cam lobe or the portion of the lobe that lies between the nose and the base circle on either side.
GROSS VALVE LIFT:
This is obtained by multiplying the cam lift by the rocker arm ratio. Rocker arm production tolerances can vary this figure by as much as +/- .015".
HARDENABLE IRON LIFTERS:
A cam follower made from high quality iron alloy. This special alloy is compatible with cast iron billet camshafts. The entire body of the hardenable iron lifter is hard as compared to the chilled iron lifter where only the base is hardened.
HYDRAULIC VALVE LIFTERS:
These lifters are designed to maintain zero lash in the valve train mechanism. Their advantages include quieter engine operation and elimination of the periodic adjustment required to maintain proper lash as with solid valve lifters. Hydraulic lifters do, however, maintain a constant pressure on the camshaft, which solid lifters do not; therefore, the antiscuff properties of lubricating oils are more critical with hydraulic lifters.
IMPROVED STOCK CAMS (CHEATER CAMS):
The improved stock cam has stock lift and duration but the flanks are modified so that they are faster acting. This process adds about a 5% increase in the area under the lift curve. This means there will be a power increase during the entire RPM range of the engine. This type of grind works very well in engines that have fuel injection systems that run off of manifold vacuum and are therefore very sensitive to camshaft duration changes.
INDUCTION HARDENING:
A process of electrical heat treating whereby an object is placed inside a coil of heavy wire through which high frequency current is passed. Through the electrical properties of this induction coil, the object inside the coil becomes cherry red almost instantly and is then quenched in oil.
INTERFERENCE FIT:
In a dual spring combination where the outside diameter of the inner spring and the inside diameter of the outer spring nearly approximate each other so that there is a slight press fit between the 2 springs. This produces a dampening effect on valve spring vibration and surge.
LASH (VALVE LASH):
This is the clearance between the base circle of the camshaft lobe and the camshaft follower or tappet.
LIFT GRAPH:
By installing the camshaft in a block or head, the mechanic can plot the lift of the cam in relation to each degree of camshaft rotation by installing a dial indicator on the cam follower or tappet and a degree wheel on the crankshaft. All that is necessary is to rotate the crankshaft every 5 degrees and take a reading on the dial indicator at each of these intervals and transfer the readings to the graph paper.
LIFTER PRINT (CAM PRINT):
The amount of travel the cam lobe has across the lifter face. Lifter diameter determines flank velocity.
LOBE:
The lobe is eccentric to the cam bearings of the camshaft and transmits a lifting motion through the valve train to operate the valves. The design of the lobe determines the usage of the camshaft. (I.e. street use or all out competition).
LOBE CENTERS-CAM:
The distance measured in degrees between the centerline of the intake lobe and the centerline of the exhaust lobe in the same cylinder.
LOBE CENTERLINES-VALVE:
The point at which the valve is fully open. For example, full intake lobe lift at 110 deg. ATDC. full exhaust lobe lift at 110 deg. BTDC. This camshaft was ground with 110 deg. lobe centers and is timed straight up. It is neither advanced nor retarded. Another example, full intake lobe lift at 105 deg. ATDC. full exhaust lobe lift at 115 deg. BTDC. This camshaft was ground also on 110 deg. lobe centers but is advanced 5 crankshaft degrees.
LOBE TAPER:
This is the amount by which the diameter of the front of the base circle is different from the diameter of the rear of the base circle. The amount of taper can be anywhere from zero to .003" depending on the engine. If the forward side of lobe is greater than the rear side we say that the cam has taper left (TL). If the back side of the lobe is greater than the front side then we say that the cam has taper right (TR). Lobe taper has a dramatic effect on the speed of rotation of the lifter. If the lifter does not rotate at the proper speed, premature lifter and cam wear will occur.
NET VALVE LIFT:
The actual lift of the valve. This lift can be determined by subtracting the valve lash dimension from the gross valve lift figure. Rocker arm production tolerances can vary this figure by much as +/-.015".
NITRIDING:
Gas nitriding is a surface heat treatment that leaves a hard case on the surface of the cam. This hard case is typically twice the hardness of the core material up to .010" deep. This process is accomplished by placing the cam into a sealed chamber that is heated to approximately 950 degrees F and filled with ammonia gas. At this temperature a chemical reaction occurs between the ammonia and the cam metal to form ferrous nitride on the surface of the cam. During this reaction, diffusion of the ferrous-nitride into the cam occurs which leads to the approximate .010" case depth. The ferrous-nitride is a ceramic compound that accounts for its hardness. It also has some lubricity when sliding against other parts. The nitriding process raises and lowers the chamber temperature slowly so that the cam is not thermally shocked. Because of its low heat-treat temperature no loss of core hardness is seen. Gas nitriding was originally conceived where sliding motion between two parts takes place repeatedly so is therefore directly applicable to solving camshaft wear problems.
NOSE OF THE LOBE:
The highest portion of the cam lobe from the base circle (full lift position). Overhead cam engine. In this type engine the camshaft is positioned above the valves.
OHC:
Overhead cam engine. In this type engine the camshaft is positioned above the valves. (i.e. 4.6 SOHC and DOHC)
OHV (PUSHROD ENGINES):
Overhead valve engines. In this type of engine the camshaft is positioned beneath the valves. (i.e. 302 Ford, 346 GM LS1)
OVERLAP:
A situation where both the intake and exhaust valves are open at the same time when the piston is at top dead center on the exhaust stroke. The greater the seat duration is on the intake and exhaust lobes, the greater the overlap will be in degrees.
PARKERIZING:
A thermo-chemical application whereby a nonmetallic, oil-absorptive coating is applied to the outside surface of the camshaft. This permits rapid break-in without scuffing the cawhere sliding motion between two parts takes place repeatedly so is therefore directly applicable to solving camshaft wear problems.
NOSE OF THE LOBE:
The highest portion of the cam lobe from the base circle (full lift position). Overhead cam engine. In this type engine the camshaft is positioned above the valves.
OHC:
Overhead cam engine. In this type engine the camshaft is positioned above the valves. (i.e. 4.6 SOHC and DOHC)
OHV (PUSHROD ENGINES):
Overhead valve engines. In this type of engine the camshaft is positioned beneath the valves. (i.e. 302 Ford, 346 GM LS1)
OVERLAP:
A situation where both the intake and exhaust valves are open at the same time when the piston is at top dead center on the exhaust stroke. The greater the seat duration is on the intake and exhaust lobes, the greater the overlap will be in degrees.
PARKERIZING:
A thermo-chemical application whereby a nonmetallic, oil-absorptive coating is applied to the outside surface of the camshaft. This permits rapid break-in without scuffing the cam lobes.
PROFERAL IRON:
A very high quality cast iron alloy. Used primarily for camshafts because of its excellent wearing ability.
ROLLER TAPPET:
The roller tappet performs the same function as the mechanical or hydraulic tappet. However, instead of sliding on the cam face, the lifter contains a roller bearing that rolls over the cam surface.
SEAT DURATION:
The total time in degrees of crankshaft rotation that the valve is off of its valve seat from when it opens until when it closes.
SPLIT OVERLAP:
An occurrence when both the intake valve and the exhaust valve are off their seats at the same time by the same amount.
SPRING FATIGUE:
Valve springs have a tendency to lose their tension after being run in an engine for certain periods of time, because of the tremendous stress they are under. At 6,000 RPM, for example, each spring must cycle 50 times per second. The tremendous heat generated by this stress eventually effects the heat-treating of the spring wire and causes the springs to take a slight set (drop in pressure).
SPRING SURGE:
The factor which causes unpredictable valve spring behavior at high reciprocating frequencies. It's caused by the inertia effect of the individual coils of the valve spring. At certain critical engine speeds, the vibrations caused by the cam movement excite the natural frequency characteristics of the valve spring and this surge effect substantially reduces the available static spring load. In other words, these inertia forces oppose the valve spring tension at critical speeds.
The above terms that are commonly tossed around about camshafts is courtesy of Elgin Cams.
Now we need to try to put all this together in finding out how it relates to engine performance. So the following segments will be to help in seeing how a typical 4 stroke engine works.
Timing Tutorial Help:
Competition Cams Valve Timing Tutorial
There are 4 simple strokes to an engine: Power, Exhaust, Intake, and Compression.
First, there is the power stroke, which is created after the spark ignites the compressed air/fuel mixture the piston is pushed downwards and relates the power to the crankshaft.
Second, there is the exhaust stroke where the piston is now coming up and the exhaust valve opens to push the excess air out the exhaust port into the exhaust manifold.
Third, there is the intake stroke in which air is pushed down into cylinder as it travels downward.
Fourth, there is the compression stroke in which the piston moves upwards to compress the air/fuel mixture that entered the cylinder on the previous stroke.
One should notice that the intake opening typically happens before top dead center (BTDC) and the intake closing typically occurs after top dead center (ATDC). The exhaust opening typically happens before bottom dead center and the exhaust closing typically occurs after top dead center (ATDC).
I will discuss this a little better and try to combine the strokes with the valve timing.
For simplicity I will start with the power stroke. The piston has just been "exploded" downwards to transmit all the power to the crankshaft to rotate it. Before the piston reaches the bottom, the exhaust valve begins to open in order to begin scavenging the exhaust, and after the power stroke passes bottom dead center, the exhaust stroke begins. The reason the exhaust valve will open before the piston reaches the bottom of its travel is because cylinder pressure is much higher, even at this point, than atmospheric pressure. This helps scavenge some of the exhaust out the exhaust port.
As the piston is coming back up to push out the extra gasses out the exhaust, the exhaust valve opens up fully and then begins to close as the piston approaches top dead center. Just before the piston gets to the top and the exhaust valve closes, the intake valve begins to open. At this point, called overlap, both the intake and exhaust valve are open. The exhaust valve closes a little after top dead center (ATDC), which is when the intake stroke begins.
The intake stroke is where the intake valve continues to open and air is pushed in from the atmospheric pressure. The intake valve continues to stay open until just after the piston reached the bottom of its travel, (ABDC). After top dead center and after the intake valve closes, the compression stroke begins to compress all the air/fuel that was just entered into the cylinder. The ignition occurs a little before the piston gets back up to the top dead center position, to continue right into the power stroke. The cycle repeats over and over. Next, the individual valve timing will be explained.
More Individual Valve Timing:
Intake Opening Events:
The intake open timing can affect manifold vacuum, throttle response, gas usage, and emissions.
An early opening intake valve at low speeds, coupled with high vacuum situations can cause exhaust gas reversion to exit out of the early opening intake valve. This happens because as the piston is coming up on the exhaust stroke to push out the extra gasses, it will have enough force to push the exhaust gas into the intake valve, if it opens up to early.
A later opening intake valve, in conjunction with the exhaust valve timing, reduces the amount of overlap. The later opening intake valve will help at lower RPM and usually helps manifold vacuum, assuming it is in tune with the other valve events.
The higher the RPM desired for a particular power band the air demand needs to increase. A early intake valve opening allows the incoming air to have more time to fill the cylinder. At higher RPMS, the exhaust gases that are being pushed out help pull some of the early intake air charge out the exhaust valve, and helps get rid of any remaining gasses. This type of purging can lead to a slightly rougher idle and slightly more gas consumption.
Intake Closing Events:
The earlier the intake valve closes the more cranking pressure you will get. This leads to what many refer to as more low-end torque and throttle response, which typically will give the engine a broader torque curve. An early intake closing also uses the combustion more efficiently and reduces emissions as well, and therefore helps fuel consumption.
But when the RPM increases or the power band desired is higher, the incoming air charge has more momentum behind it. This demands a later intake valve closing event to try to get as much air in as possible to be combusted. If the intake valve is closed to late, the once incoming air and all its momentum may have time to escape. Valve timing is critical here.
The ultimate goal is to get the intake valve to close right as the intake air charge quits flowing into the cylinder. Getting the valve events timed in perfect order is very difficult from a mechanical point of view. The valves cannot open and close like a light switch. They have to be managed smoothly at a certain rate, or you risk valve bounce, excessive valve train wear and noise.
Exhaust Opening Events:
In contrast to the intake closing events, the exhaust opening events probably have the least importance in valve timing. As they say though, it is last but definitely not least.
Cylinder pressure will be decreased if the exhaust valve opens to early. The exhaust valve typically opens near the bottom of the power stroke pushing the piston downwards, so you can see why if you open it up to early it can decrease cylinder pressure. However, the exhaust needs to open up early enough to help gas scavenging for the cylinder that just going through the power phase of the stroke.
One may see that higher RPM engines will have even earlier exhaust openings because at high RPM, that cylinder pressure is typically already used by the time it gets half-way down the stroke. So, inversely you will see lower RPM engines have a later exhaust valve opening, more near the bottom of the power stroke, keeping increased cylinder pressure longer, in turn, providing a more efficient burn, aka, emissions.
Exhaust Closing Events:
An early exhaust valve closing can provide a smoother idle and lower RPM power, which is the same principle that a late intake opening creates. It reduces overlap period, in which both intake and exhaust valves are open, intake opening/exhaust closing.
It is just the opposite; a late exhaust valve closing is just like opening up the intake valve early. It increases overlap, which if too much can cause the incoming intake air charged to be pushed back into the intake ports of the head. It also can cause the incoming air to be pushed out the exhaust, if the exhaust valve closes too late in relation to the intake valve opening events.
A late exhaust closing valve is not all bad. At higher RPMS and power bands, it can get rid of the excess gas out into the exhaust port, and also can provide a higher vacuum in the intake at higher RPMS.
You can see how getting each opening and closing event balanced can effect an engines characteristics.
Summary:
If you take these generalities, a camshaft with low-end, broad power band, and good idle qualities will prefer a later intake valve opening, early intake valve closing, later exhaust valve openings, and early exhaust valve closing.
On the contrary, a camshaft that desires more RPM and a higher power band will prefer early intake valve opening, late intake valve closing, early exhaust valve openings, and late exhaust valve closing.
Individual valve events are very important in a camshaft and are often overlooked. Of course, they are no the only factor in determining where power and driving quality is made.
Further Explanation For Camshaft Terms:
Lobe Separation Angle (LSA):
Many will see on their camshaft timing card a number labeled as LSA. This is the Lobe Separation Angle. It has many effects on an engine and I will explain what decreasing and increasing LSA can do to the engine parameters. Lobe separation angle defined as a measurement in degrees of the distance between the max lift on the exhaust and intake camshaft lobes, and is measured in camshaft degrees. It cannot be changed once it is ground.
First off, this is general information and there are other factors, but the following will be a good rule of thumb.
A 110 degree LSA is considered a tight lobe separation angle compared to a 114 degree LSA.
A 114 degree LSA is considered a wider lobe separation angle compared to a 110 degree LSA.
We will use and compare these examples below.
The tighter LSA of 110 degrees:
- Increases cylinder pressure, cranking pressure, dynamic pressure, which can increase octane requirements.
- Increases valve overlap.
- Narrows the power band, and put torque at a more midrange RPM.
- Increases speed of engine revving.
- Initially gives quicker throttle response.
- Reduces idle quality and creates less vacuum.
- Decreases piston to valve clearance.
- Reacts better for carbureted engines.*
The wider LSA of 114 degrees:
- Decreases cylinder pressure, cranking pressure, dynamic pressure, which will decrease octane requirements.
- Decreases valve overlap.
- Widens the power band, and put torque at a higher RPM being more peaky.
- Decreases speed of engine revv
If corrections need to be made, feel free to let me know.Post One will include terms and valve timing explained along with extra links.
Post Two will be continued and include common 5.0L camshaft specifications.
After reading much of the following, you will quickly realize that a camshaft is the brains of an engine and how IMPORTANT it is to get a camshaft to match your goals and engine combination. This is where custom cam grinders shine
Contact either of the following to find out more, and how it is money well spent.Ed Curtis ([email protected]) @ www.flowtechinduction.com
Buddy Rawls ([email protected]) @ http://www.wighat.com/fcr3/index.html
Camshaft Term Glossary
ABDC:
Degrees after bottom dead center.
ATDC:
Degrees after top dead center.
AREA UNDER THE CAM LIFT CURVE:
The area under the bell shaped curve with lift on the vertical axis and degrees of rotation on the horizontal axis. The greater the area under the lift curve, the greater is the lift and/or duration at some point on the camshaft profile.
BASE CIRCLE:
The concentric or round portion of the cam lobe where the valve lash adjustments must be made. (Also known as the heel.)
BBDC:
Degrees before bottom dead center.
BTDC:
Degrees before top dead center.
CAM FOLLOWER/TAPPET:
Usually a flat faced or roller companion to the camshaft that transfers the action of the camshaft to the rest of the valve train by sliding or rolling on the cam lobe surface.
CAM LIFT:
This is the maximum distance that the cam pushes the follower when the valve is open. This is different from valve lift. See "GROSS VALVE LIFT."
CAM MASTER:
After the design of the cam is computed, it is transferred to a precision template or master. The master is then installed in the cam grinding machine to generate the shape of the lobes of the production cam.
CAM PROFILE:
The actual shape of the cam lobe.
CAMSHAFT:
A shaft containing many cams that covert rotary motion to reciprocating (lifting) motion. For every 2 revolutions of the crankshaft, the camshaft rotates 1 revolution. The lobes on the camshaft actuate the valve train in relation to the piston movement in an internal combustion engine. The camshaft determines when the valves open and close how long they stay open and how far they open.
CARBURIZING:
Gas carburizing is a method to heat-treat steel camshaft billets. In this method, the camshaft is placed in a carbon gas atmosphere furnace and heated to the proper temperature. When the shaft has absorbed the proper amount of carbon, it is removed from the furnace and quenched to the proper temper.
CAST BILLET:
A term used to describe a camshaft that is made from a casting. The material for the casting is a special grade of iron alloy called "Proferal." GLOSSARY OF CAMSHAFT TERMS (CONTINUED)
CHEATER CAMS:
See "Improved Stock Cams".
CHILLED IRON LIFTER:
A cam follower made from high quality iron alloy that is heat treated by pouring the molten iron into a honeycomb mold with a chilled steel plate at the bottom to heat treat the face of the lifter. It is compatible with steel and hardface overlay cams only.
CLEARANCE RAMPS:
The portion of the cam lobe adjacent to the base circle that lifts at a constant slow speed. It's purpose, in theory, is to compensate for small deflections and take up the slack in the valve train created by the valve lash. The opening ramp takes up all clearances in the valve train and causes the valve to be on the verge of opening. The closing ramp begins when the valve touches the valve seat and ends when the tappet returns to the base circle. Ramp designs have a tremendous effect on power output and valve train reliability.
COIL BIND:
A valve spring that has been compressed to the point where the coils are stacked solid and there is no space left between the coils. The valve cannot open any further at when this happens.
CONCENTRIC:
Running true or having the same center. In camshaft terminology, the cam bearings and lobes are concentric to each other when the cam is straight and there is .001" or less runout between all the cam lobes and bearings.
DURATION AT .050":
The amount of time measured in degrees of crankshaft rotation from when the valve is open .050" far until it is .050" from closing.
FLAME HARDENING:
A heat treating process whereby a camshaft is exposed to an open flame and then quenched (cooled in oil).
FLANKS:
The sides of the cam lobe or the portion of the lobe that lies between the nose and the base circle on either side.
GROSS VALVE LIFT:
This is obtained by multiplying the cam lift by the rocker arm ratio. Rocker arm production tolerances can vary this figure by as much as +/- .015".
HARDENABLE IRON LIFTERS:
A cam follower made from high quality iron alloy. This special alloy is compatible with cast iron billet camshafts. The entire body of the hardenable iron lifter is hard as compared to the chilled iron lifter where only the base is hardened.
HYDRAULIC VALVE LIFTERS:
These lifters are designed to maintain zero lash in the valve train mechanism. Their advantages include quieter engine operation and elimination of the periodic adjustment required to maintain proper lash as with solid valve lifters. Hydraulic lifters do, however, maintain a constant pressure on the camshaft, which solid lifters do not; therefore, the antiscuff properties of lubricating oils are more critical with hydraulic lifters.
IMPROVED STOCK CAMS (CHEATER CAMS):
The improved stock cam has stock lift and duration but the flanks are modified so that they are faster acting. This process adds about a 5% increase in the area under the lift curve. This means there will be a power increase during the entire RPM range of the engine. This type of grind works very well in engines that have fuel injection systems that run off of manifold vacuum and are therefore very sensitive to camshaft duration changes.
INDUCTION HARDENING:
A process of electrical heat treating whereby an object is placed inside a coil of heavy wire through which high frequency current is passed. Through the electrical properties of this induction coil, the object inside the coil becomes cherry red almost instantly and is then quenched in oil.
INTERFERENCE FIT:
In a dual spring combination where the outside diameter of the inner spring and the inside diameter of the outer spring nearly approximate each other so that there is a slight press fit between the 2 springs. This produces a dampening effect on valve spring vibration and surge.
LASH (VALVE LASH):
This is the clearance between the base circle of the camshaft lobe and the camshaft follower or tappet.
LIFT GRAPH:
By installing the camshaft in a block or head, the mechanic can plot the lift of the cam in relation to each degree of camshaft rotation by installing a dial indicator on the cam follower or tappet and a degree wheel on the crankshaft. All that is necessary is to rotate the crankshaft every 5 degrees and take a reading on the dial indicator at each of these intervals and transfer the readings to the graph paper.
LIFTER PRINT (CAM PRINT):
The amount of travel the cam lobe has across the lifter face. Lifter diameter determines flank velocity.
LOBE:
The lobe is eccentric to the cam bearings of the camshaft and transmits a lifting motion through the valve train to operate the valves. The design of the lobe determines the usage of the camshaft. (I.e. street use or all out competition).
LOBE CENTERS-CAM:
The distance measured in degrees between the centerline of the intake lobe and the centerline of the exhaust lobe in the same cylinder.
LOBE CENTERLINES-VALVE:
The point at which the valve is fully open. For example, full intake lobe lift at 110 deg. ATDC. full exhaust lobe lift at 110 deg. BTDC. This camshaft was ground with 110 deg. lobe centers and is timed straight up. It is neither advanced nor retarded. Another example, full intake lobe lift at 105 deg. ATDC. full exhaust lobe lift at 115 deg. BTDC. This camshaft was ground also on 110 deg. lobe centers but is advanced 5 crankshaft degrees.
LOBE TAPER:
This is the amount by which the diameter of the front of the base circle is different from the diameter of the rear of the base circle. The amount of taper can be anywhere from zero to .003" depending on the engine. If the forward side of lobe is greater than the rear side we say that the cam has taper left (TL). If the back side of the lobe is greater than the front side then we say that the cam has taper right (TR). Lobe taper has a dramatic effect on the speed of rotation of the lifter. If the lifter does not rotate at the proper speed, premature lifter and cam wear will occur.
NET VALVE LIFT:
The actual lift of the valve. This lift can be determined by subtracting the valve lash dimension from the gross valve lift figure. Rocker arm production tolerances can vary this figure by much as +/-.015".
NITRIDING:
Gas nitriding is a surface heat treatment that leaves a hard case on the surface of the cam. This hard case is typically twice the hardness of the core material up to .010" deep. This process is accomplished by placing the cam into a sealed chamber that is heated to approximately 950 degrees F and filled with ammonia gas. At this temperature a chemical reaction occurs between the ammonia and the cam metal to form ferrous nitride on the surface of the cam. During this reaction, diffusion of the ferrous-nitride into the cam occurs which leads to the approximate .010" case depth. The ferrous-nitride is a ceramic compound that accounts for its hardness. It also has some lubricity when sliding against other parts. The nitriding process raises and lowers the chamber temperature slowly so that the cam is not thermally shocked. Because of its low heat-treat temperature no loss of core hardness is seen. Gas nitriding was originally conceived where sliding motion between two parts takes place repeatedly so is therefore directly applicable to solving camshaft wear problems.
NOSE OF THE LOBE:
The highest portion of the cam lobe from the base circle (full lift position). Overhead cam engine. In this type engine the camshaft is positioned above the valves.
OHC:
Overhead cam engine. In this type engine the camshaft is positioned above the valves. (i.e. 4.6 SOHC and DOHC)
OHV (PUSHROD ENGINES):
Overhead valve engines. In this type of engine the camshaft is positioned beneath the valves. (i.e. 302 Ford, 346 GM LS1)
OVERLAP:
A situation where both the intake and exhaust valves are open at the same time when the piston is at top dead center on the exhaust stroke. The greater the seat duration is on the intake and exhaust lobes, the greater the overlap will be in degrees.
PARKERIZING:
A thermo-chemical application whereby a nonmetallic, oil-absorptive coating is applied to the outside surface of the camshaft. This permits rapid break-in without scuffing the cawhere sliding motion between two parts takes place repeatedly so is therefore directly applicable to solving camshaft wear problems.
NOSE OF THE LOBE:
The highest portion of the cam lobe from the base circle (full lift position). Overhead cam engine. In this type engine the camshaft is positioned above the valves.
OHC:
Overhead cam engine. In this type engine the camshaft is positioned above the valves. (i.e. 4.6 SOHC and DOHC)
OHV (PUSHROD ENGINES):
Overhead valve engines. In this type of engine the camshaft is positioned beneath the valves. (i.e. 302 Ford, 346 GM LS1)
OVERLAP:
A situation where both the intake and exhaust valves are open at the same time when the piston is at top dead center on the exhaust stroke. The greater the seat duration is on the intake and exhaust lobes, the greater the overlap will be in degrees.
PARKERIZING:
A thermo-chemical application whereby a nonmetallic, oil-absorptive coating is applied to the outside surface of the camshaft. This permits rapid break-in without scuffing the cam lobes.
PROFERAL IRON:
A very high quality cast iron alloy. Used primarily for camshafts because of its excellent wearing ability.
ROLLER TAPPET:
The roller tappet performs the same function as the mechanical or hydraulic tappet. However, instead of sliding on the cam face, the lifter contains a roller bearing that rolls over the cam surface.
SEAT DURATION:
The total time in degrees of crankshaft rotation that the valve is off of its valve seat from when it opens until when it closes.
SPLIT OVERLAP:
An occurrence when both the intake valve and the exhaust valve are off their seats at the same time by the same amount.
SPRING FATIGUE:
Valve springs have a tendency to lose their tension after being run in an engine for certain periods of time, because of the tremendous stress they are under. At 6,000 RPM, for example, each spring must cycle 50 times per second. The tremendous heat generated by this stress eventually effects the heat-treating of the spring wire and causes the springs to take a slight set (drop in pressure).
SPRING SURGE:
The factor which causes unpredictable valve spring behavior at high reciprocating frequencies. It's caused by the inertia effect of the individual coils of the valve spring. At certain critical engine speeds, the vibrations caused by the cam movement excite the natural frequency characteristics of the valve spring and this surge effect substantially reduces the available static spring load. In other words, these inertia forces oppose the valve spring tension at critical speeds.
The above terms that are commonly tossed around about camshafts is courtesy of Elgin Cams.
Now we need to try to put all this together in finding out how it relates to engine performance. So the following segments will be to help in seeing how a typical 4 stroke engine works.
Timing Tutorial Help:
Competition Cams Valve Timing Tutorial
There are 4 simple strokes to an engine: Power, Exhaust, Intake, and Compression.
First, there is the power stroke, which is created after the spark ignites the compressed air/fuel mixture the piston is pushed downwards and relates the power to the crankshaft.
Second, there is the exhaust stroke where the piston is now coming up and the exhaust valve opens to push the excess air out the exhaust port into the exhaust manifold.
Third, there is the intake stroke in which air is pushed down into cylinder as it travels downward.
Fourth, there is the compression stroke in which the piston moves upwards to compress the air/fuel mixture that entered the cylinder on the previous stroke.
One should notice that the intake opening typically happens before top dead center (BTDC) and the intake closing typically occurs after top dead center (ATDC). The exhaust opening typically happens before bottom dead center and the exhaust closing typically occurs after top dead center (ATDC).
I will discuss this a little better and try to combine the strokes with the valve timing.
For simplicity I will start with the power stroke. The piston has just been "exploded" downwards to transmit all the power to the crankshaft to rotate it. Before the piston reaches the bottom, the exhaust valve begins to open in order to begin scavenging the exhaust, and after the power stroke passes bottom dead center, the exhaust stroke begins. The reason the exhaust valve will open before the piston reaches the bottom of its travel is because cylinder pressure is much higher, even at this point, than atmospheric pressure. This helps scavenge some of the exhaust out the exhaust port.
As the piston is coming back up to push out the extra gasses out the exhaust, the exhaust valve opens up fully and then begins to close as the piston approaches top dead center. Just before the piston gets to the top and the exhaust valve closes, the intake valve begins to open. At this point, called overlap, both the intake and exhaust valve are open. The exhaust valve closes a little after top dead center (ATDC), which is when the intake stroke begins.
The intake stroke is where the intake valve continues to open and air is pushed in from the atmospheric pressure. The intake valve continues to stay open until just after the piston reached the bottom of its travel, (ABDC). After top dead center and after the intake valve closes, the compression stroke begins to compress all the air/fuel that was just entered into the cylinder. The ignition occurs a little before the piston gets back up to the top dead center position, to continue right into the power stroke. The cycle repeats over and over. Next, the individual valve timing will be explained.
More Individual Valve Timing:
Intake Opening Events:
The intake open timing can affect manifold vacuum, throttle response, gas usage, and emissions.
An early opening intake valve at low speeds, coupled with high vacuum situations can cause exhaust gas reversion to exit out of the early opening intake valve. This happens because as the piston is coming up on the exhaust stroke to push out the extra gasses, it will have enough force to push the exhaust gas into the intake valve, if it opens up to early.
A later opening intake valve, in conjunction with the exhaust valve timing, reduces the amount of overlap. The later opening intake valve will help at lower RPM and usually helps manifold vacuum, assuming it is in tune with the other valve events.
The higher the RPM desired for a particular power band the air demand needs to increase. A early intake valve opening allows the incoming air to have more time to fill the cylinder. At higher RPMS, the exhaust gases that are being pushed out help pull some of the early intake air charge out the exhaust valve, and helps get rid of any remaining gasses. This type of purging can lead to a slightly rougher idle and slightly more gas consumption.
Intake Closing Events:
The earlier the intake valve closes the more cranking pressure you will get. This leads to what many refer to as more low-end torque and throttle response, which typically will give the engine a broader torque curve. An early intake closing also uses the combustion more efficiently and reduces emissions as well, and therefore helps fuel consumption.
But when the RPM increases or the power band desired is higher, the incoming air charge has more momentum behind it. This demands a later intake valve closing event to try to get as much air in as possible to be combusted. If the intake valve is closed to late, the once incoming air and all its momentum may have time to escape. Valve timing is critical here.
The ultimate goal is to get the intake valve to close right as the intake air charge quits flowing into the cylinder. Getting the valve events timed in perfect order is very difficult from a mechanical point of view. The valves cannot open and close like a light switch. They have to be managed smoothly at a certain rate, or you risk valve bounce, excessive valve train wear and noise.
Exhaust Opening Events:
In contrast to the intake closing events, the exhaust opening events probably have the least importance in valve timing. As they say though, it is last but definitely not least.
Cylinder pressure will be decreased if the exhaust valve opens to early. The exhaust valve typically opens near the bottom of the power stroke pushing the piston downwards, so you can see why if you open it up to early it can decrease cylinder pressure. However, the exhaust needs to open up early enough to help gas scavenging for the cylinder that just going through the power phase of the stroke.
One may see that higher RPM engines will have even earlier exhaust openings because at high RPM, that cylinder pressure is typically already used by the time it gets half-way down the stroke. So, inversely you will see lower RPM engines have a later exhaust valve opening, more near the bottom of the power stroke, keeping increased cylinder pressure longer, in turn, providing a more efficient burn, aka, emissions.
Exhaust Closing Events:
An early exhaust valve closing can provide a smoother idle and lower RPM power, which is the same principle that a late intake opening creates. It reduces overlap period, in which both intake and exhaust valves are open, intake opening/exhaust closing.
It is just the opposite; a late exhaust valve closing is just like opening up the intake valve early. It increases overlap, which if too much can cause the incoming intake air charged to be pushed back into the intake ports of the head. It also can cause the incoming air to be pushed out the exhaust, if the exhaust valve closes too late in relation to the intake valve opening events.
A late exhaust closing valve is not all bad. At higher RPMS and power bands, it can get rid of the excess gas out into the exhaust port, and also can provide a higher vacuum in the intake at higher RPMS.
You can see how getting each opening and closing event balanced can effect an engines characteristics.
Summary:
If you take these generalities, a camshaft with low-end, broad power band, and good idle qualities will prefer a later intake valve opening, early intake valve closing, later exhaust valve openings, and early exhaust valve closing.
On the contrary, a camshaft that desires more RPM and a higher power band will prefer early intake valve opening, late intake valve closing, early exhaust valve openings, and late exhaust valve closing.
Individual valve events are very important in a camshaft and are often overlooked. Of course, they are no the only factor in determining where power and driving quality is made.
Further Explanation For Camshaft Terms:
Lobe Separation Angle (LSA):
Many will see on their camshaft timing card a number labeled as LSA. This is the Lobe Separation Angle. It has many effects on an engine and I will explain what decreasing and increasing LSA can do to the engine parameters. Lobe separation angle defined as a measurement in degrees of the distance between the max lift on the exhaust and intake camshaft lobes, and is measured in camshaft degrees. It cannot be changed once it is ground.
First off, this is general information and there are other factors, but the following will be a good rule of thumb.
A 110 degree LSA is considered a tight lobe separation angle compared to a 114 degree LSA.
A 114 degree LSA is considered a wider lobe separation angle compared to a 110 degree LSA.
We will use and compare these examples below.
The tighter LSA of 110 degrees:
- Increases cylinder pressure, cranking pressure, dynamic pressure, which can increase octane requirements.
- Increases valve overlap.
- Narrows the power band, and put torque at a more midrange RPM.
- Increases speed of engine revving.
- Initially gives quicker throttle response.
- Reduces idle quality and creates less vacuum.
- Decreases piston to valve clearance.
- Reacts better for carbureted engines.*
The wider LSA of 114 degrees:
- Decreases cylinder pressure, cranking pressure, dynamic pressure, which will decrease octane requirements.
- Decreases valve overlap.
- Widens the power band, and put torque at a higher RPM being more peaky.
- Decreases speed of engine revv
