Selecting a camshaft is one of the most important decisions you make when building a max-performance engine because the cam controls crucial timing events. And those events need to occur at the proper time in the engine’s cycle and in conjunction with the engine’s other component operations. If these events do not occur at the correct time, the engine does not reach its performance potential.
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Once you decide to change the cam, you are faced with a vast selection of manufacturers, profiles, designs, and options. The cam dictates most of the valvetrain specs and should work with the amount of air that the cylinder head can flow and with the intake manifold/induction system. The camshaft is part of the engine’s short block, so cranks, pistons, rods, and valvetrain need to be considered.
On the other hand, cylinder heads are very popular. With the Magnum versions, installing a cam and tappets should be done before the heads are installed because after the heads are installed, it is very difficult to install the tall, hydraulic tappets under the edge of the head.
Of the major parts within the short block, the camshaft is substantially different between A-engines and Magnum engines. The A-engine has a long nose at the front of the cam; the Magnum engine has a short nose. This difference is because the A-engine has a mechanical fuel pump eccentric-mounted on the nose and the Magnum engine does not use a mechanical fuel pump.
A few Mopar Performance crate engines, however, were based on the Magnum engine, and they were designed for use with a cam that had a long nose and a mechanical fuel pump.
A-engine and Magnum cams look similar because the difference in overall length is only about 1/4 inch. The distributor drive gear is located at the rear of the cam along with a small number-5 bearing journal. The other four journals are basically the same size (just under 2 inches). Cams are made of cast iron or steel. Most aftermarket cams are stamped with profile numbers or manufacturer numbers, but production cams have no actual stamped or cast numbers.
Production cams were mechanical (1964–1967), hydraulic (1967– 1985 and 1991), and hydraulic roller (1992–2003). It is not easy to differentiate them.
If you have a small-block cam but don’t know which one, you use cam lift to help identify it. (Measure lift at the tappet, if possible, and multiply by 1.5 to use the chart on page 52.)
If you have tappets that operate with the cam, identifying your cam style is easier.
The lift number can also help identify aftermarket profiles if no stamped identification numbers are visible.
Comp, Crane, Isky, Bullet, Edelbrock, and other cam manufacturers offer a wide range of profiles for flat tappets, hydraulic rollers, mechanical rollers, etc. Assuming that the cylinder head is matched to the cam, the more valve lift you put in, the more power the engine makes. However, remember that higher lifts create longer durations, and long durations can cause serious problems with street engines and drivability.
As the valve lift increases, you need to select the appropriate cam. A base performance cam is hydraulic, and then you move to hydraulic roller cams, to mechanical cams, and to mechanical roller cams. Billet cams tend to focus on the racing end of the cam scale.
All small-blocks are four-stroke engines, which have four phases to the engine cycle: intake, compression, power, and exhaust. Each phase is 180 crankshaft degrees. This means that the full engine cycle takes two full revolutions of the crank (360 degrees makes one complete revolution). Because the cycle takes two revolutions, the camshaft runs at half-crank speed and the cam sprocket is twice as large as the crank sprocket.
The cam lift, or lobe lift, is the distance that the tappet moves upward in the tappet bore. However, it is more common to discuss valve lift, which is the distance that the valve moves off the valveseat. These two types of lift are influenced by the rocker arm ratio (typically 1.5 or 1.6). Valve lift tends to be the most popular lift number, and it is also the easiest to measure directly.
Duration is defined as the number of crank degrees that the intake and exhaust valves are open off their seat. Advertised duration is the most popular and probably the most common. It is loosely defined as the point at which the tappet is approximately .012 to .017 inch off the seat (zero position), but some aftermarket companies use a tighter tolerance, maybe .005 inch.
The second type of duration is called “duration at fifty,” or “duration at .050 inch.” With this duration, the tappet is .050 inch off its zero position. The duration at .050 is always smaller than the advertised duration, but it’s much more useful in all-out race cams and engines.
The engine cycle includes four cam events: intake opens, intake closes, exhaust opens, and exhaust closes. These four events are measured in degrees relative to TDC or BDC. The cam’s duration can be calculated if you know the event measurements.
A cam’s overlap is the amount of time that both the intake and exhaust valves are open. It is defi ned as the sum of the intake opens event (before TDC) and the exhaust closes event (after TDC). Street cams have low overlaps and race cams have high overlaps.
After a manufacturer grinds a cam, there is only one specifi cation that you can change, the installed cam centerline. This is the relationship of the cam to the crankshaft, sometimes called the intake centerline.
The manufacturer grinds the cam centerline (or lobe centers; see sidebar “Camshaft Terms”) into the cam, and after it’s ground, you can’t change it. You can, however, adjust cam advance or retard.
For example, a 340 may be ground on 114-degree centers and installed at 114 degrees intake. By definition, the exhaust is also at 114 degrees. So, if you install this cam 5-degrees advanced, the intake becomes 109 degrees and the exhaust becomes 119 degrees.
Valvetrain geometry starts with the camshaft location and the tappet angle (all production small-blocks use a 59-degree tappet angle). This geometry is suitable for many high-performance street applications, but as you get into all-out racing cylinder heads and racing valvetrains, improvements can be made.
Most valvetrain issues become apparent at high RPM, and that’s usually more than 7,500 rpm. If your engine generally runs more RPM and makes more horsepower, the fi rst major improvement is changing the tappet angle.
If you draw a straight line from the race rocker arm pivot in the typical race cylinder head to the center of the camshaft, the tappet angle is 48 degrees. It is very diffi cult and very expensive to change to this angle on an existing block. Knowing this, Mopar Performance added material to its race blocks to allow for a 48-degree tappet. The casting is designed to allow machining of the race blocks with either-style tappet. If you have a race block machined for 48-degree tappets, you must use camshafts that are ground for 48-degree tappets.
All cams are oiled from the main bearings. Magnum engines oil the rest of the valvetrain through the pushrods from the tappets.
All A-engines oil the heads and valve gear through the block and head (machined passages). This oiling path starts at the number-2 and -4 cam journals (the cam has five). It is a good idea to be sure that any cam that you use has the number-2 and -4 cam journals drilled through and grooved to help move oil to the cylinder heads and upper valvetrain at all engine speeds.
Magnum engines use a forged steel cam and special hardened oil pump drive gear that mates to it.
These look similar to the standard A-engine gear/drive, but they should not be switched. You cannot use a standard A-engine intermediate shaft and gear on Magnum cams.
If you want to use steel cams (and, until recently, race mechanical rollers) in an A-engine, you have to change the gear to an aluminum-bronze gear. It is gold colored, which is very obvious. This aluminum-bronze gear or shaft assembly is available from Crane or Comp Cams. It also works with Magnum cams.
High-Performance and Race Cams
These are considered to be any cam that is larger than stock or is a service replacement. They are typically made by the aftermarket or Mopar Performance. You should always replace the tappets when you replace the camshaft.
Big Hydraulic The 340 cam is the largest of the production designs, so these cams start in the .450-inch lift area and go up. Big hydraulic cams may have .480- to .520-inch lift. The advertised durations tend to be in the 280- to 290-degree area.
Hydraulic Roller The hydraulic roller cam is standard in all 5.2L and 5.9L Magnum engines. The Magnum roller cam is shorter than the typical A-engine cam because the fuel pump eccentric was removed from the front of the Magnum cams.
The tappet location spider and figure-eight (dog bone) hardware does not fit the typical A-engine block. The exception is the 1988 to 1991–1992 A-engines, which had hydraulic roller cams also. To convert an A-engine to a hydraulic roller cam, use the Comp Cams or Crane conversion kit, cam, and tappets. To install bigger hydraulic roller cams in the Magnum, install better valvesprings.
The 1986–1991 318 and the 1987–1992 360 cams are at the end of the LA-engine’s long production run and they were switched to hydraulic roller cams before the basic engine conversion to the Magnum family. This makes them unique in the LA family. Crane offers cams for these engines. The 1985 and earlier cams do not work in these engines.
Mechanical Select a mechanical cam when your engine needs a cam that’s bigger than the .520-inch-lift hydraulic cam. Mechanical cams with .500-inch-lift area were produced, but lifts of .550 to .600 inch are more common.
In addition, you must install adjustable rocker arms when a mechanical cam is added. The exception is the 340 6-barrel engines, which already have adjustable rockers. Mechanical cams may also require an upgrade in valvesprings, such as a dual spring.
Mechanical Roller For the past 20 years, Pro racing classes and similar engines have used mechanical roller cams. They allow more lift without breakage than the standard mechanical. For many years, mechanical roller cams peaked at about .700- to .750-inch lift. If the cylinder heads were limited (such as stock castings that were ported or heads limited by their valve size), around .650-inch lift was more likely.
Then, better and bigger cylinder heads were introduced, and mechanical rollers grew even bigger and the valvesprings became stronger. The upper limits are still open, but valvespring loads are more than 750 pounds and valve lifts are approaching 1.00 inch. Part of the technology that allows these very large changes is the big 60-mm roller cam bearings.
Roller Cam Bearings The 50- and 60-mm roller cam bearings require their bearing bore diameter in the block to be larger; it must be much larger in the 60-mm version. Cam bearing bore cannot be increased on stock production blocks because the bulkhead does not have enough material to bore. Mopar Performance race blocks, called R3s, have material added and allow for this modification.
Cam Selection Process
Selecting the correct cam for an engine combination is dependent on a wide range of factors, so you should take a methodical and detailed approach when determining the specific cam for your engine. Be sure your cam works in conjunction with and complements the entire engine package, including heads, intake, carb, and exhaust.
If you put all that stuff into a chart, it would be so complicated that no one would ever figure it out. Instead, I have included my recommendations in two charts for each cam, the second one shows some of the engine hardware that will work.
Properly orienting the cam with the crankshaft requires some detail work so the engine performs well. The factory method of lining up the dots on the crank and cam sprockets is a starting point, but if you bought a new cam, follow the manufacturer’s recommendations. Often, an aftermarket cam must be installed in a different location. To fi nd this installation location, you need a degree wheel and a dial indicator.
Using a Degree Wheel
As I recall, high school geometry says that a circle is divided into 360 degrees. Engine builders use a degree wheel to install and centerline camshafts and to check camshaft locations relative to the crank.
My recommendation is to use the 0-180-0 version (available from Mopar Performance) because I prefer to think of the relationship of the crank to the camshaft in terms of the cam centerline, which is one number that defines one engine aspect.
The other version (0-90-0-90-0 style) is designed mainly to work with the four-event installation method, which has degrees for the four events: intake opens (IO), intake closes (IC), exhaust opens (EO), and exhaust closes (EC). You also have to consider the locations before or after TDC and BDC.
Adjusting the Centerline
After you have determined the cam’s actual centerline, slip the cam sprocket off the nose of the cam and remove the stock key. Install the new offset key and slip the sprocket back into position. It is easier to adjust the centerline using the dial indicator than it is to calculate which direction it goes, offset to the left or offset to the right. If you guess wrong and the offset is installed incorrectly, the dial indicator and degree wheel tell you.
Aligning Timing Marks
Each tooth in the cam sprocket is about 7.5 degrees wide; aligning the dots is only accurate to 7.5 degrees. The installed centerline could be 107 or 123, which is one tooth off in each direction. Therefore, if you want to install the cam at 112 or 118, you can’t get there with the lining-up-the-dots method. However, actually doing the lining-up-the-dots as the first step saves you a lot of time in the long run. It also catches a one-tooth-off error.
Degreeing the cam (centerline installation method) requires a degree wheel. Always remember that the cam needs to have a specific relationship with the number-1 piston. So the zeroing process, which is the first step, is extremely important.
When degreeing a cam, the cam movement (changing the centerline) is called advancing or retarding the cam. If you start with a 115-degree centerline, and you move the centerline toward 100 degrees, you are advancing the cam. If you move the centerline away from 100 degrees, you are retarding the cam.
A tappet is about 1 inch in diameter and 2 to 3 inches long. The face of the tappet rides directly on the lobe of the cam. Therefore, the tappets must be the same as the cam design, that is, hydraulic to hydraulic, mechanical to mechanical, etc.
The most common mode of tappet failure is scuffing. Always replace the tappets when you replace the cam and keep the tappets matched to the lobenumber-1 intake tappet on the number-1 intake lobe.
You should always replace all three pieces of the cam drive if it appears to be showing too much wear. You should replace the cam drive on high-mileage engines.
Belt, gear, silent, and roller are the four cam drive types. The belt drive is made by Jesel and should be considered a drag racing part. Several companies make gear drives but I recommend Milodon because it fits under the stock front cover (most gear drives replace the stock front cover). The silent chain is the typical production version and should be replaced for any performance application.
Crane, Comp Cams, Milodon, and Cloyes make roller or double-roller timing chains. Cloyes has several versions of the roller-chain cam drive with three or nine keyways for cam alignment, along with standard and billet gears.
Cloyes offers a hex-adjust option for the Mopar big-block but not the small-block yet, maybe soon. Any of the roller assemblies are fine for the street, but the special tensioner offered by Mopar Performance (Mancini Racing in Detroit) is a nice trick for the street: durability and accuracy over time.
Cloyes makes a multi-keyed sprocket, which is a version of the roller chain. The difference is in the two sprockets because they have more than one keyway for installation. And it doesn’t require offset keys to centerline the cam. There are often three keyways but there can be as many as five. Each keyway has a unique dot for alignment.
Magnum engines use special hardened gear on the intermediate shaft. Production A-engines use a cast-iron gear. With any steel cam (typically a roller), an aluminum-bronze gear (brass/gold in color) must be used.
Oil Pump Drive
Max-performance applications require the use of a hardened oil pump shaft and an upgraded oil pump gear. A high-volume pump places a higher load on the oil pump shaft, so it needs a hardened tip. Mopar performance offers upgraded pump driveshafts and distributor gears.
Written by Larry Shepard and Posted with Permission of CarTechBooks
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