CHRYSLER TECHNICAL INFORMATION

Engine Types | General Tips

Engine Types

Small Block, "A" Uses "20" Prefix
The basic 273-360 engines, produced in the mid 1960’s, have remained relatively unchanged as far as the valve train is concerned. The 1964-1991 engines used shaft type rocker arms, which required some special changes in the camshaft design. This was to allow oil to flow to the top of the engine and into the rocker arm shafts. Most of these early engines featured either grooved or offset holes in the second and fourth cam journals. In some instances a combination of both grooves and holes were employed. You must remember that if your engine has shaft type rocker arms, there must be some groove or oiling hole combination on the cam journals. In 1992 the Magnum version of the “A” engine was changed to a pedestal style individual rocker arm design.

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Magnum
The new Magnum engines utilize a pedestal mount rocker arm system. They come from the factory with a nonadjustable valve train and have 5/16” bolts fastening the rockers to pedestals on the heads.

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5.7L & 6.1L Hemi, Uses “112” Prefix
In 2003 Chrysler called on the legendary “Hemi” cylinder head design to begin a new era in Mopar performance. This new engine has the same familiar perpendicular valve arrangement but does not share any parts with the classic Hemi engines. Rocker arms are shaft mounted with 1.6 ratio on intake and exhaust. Two rocker shafts per head are used, which is similar to the earlier Hemi. Because of this design, different length intake and exhaust pushrods are used. The new engine also uses smaller, .842” diameter hydraulic roller lifters and a single bolt cam sprocket.

There are concerns when installing aftermarket camshafts in these engines. The factory piston has a dome and no valve reliefs. Extra caution should be taken to ensure adequate piston to valve clearance. It is also necessary to deactivate the MDS (multiple displacement system) when installing and using a performance camshaft. Computer tuning must be performed to enhance drivability.

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V10, Uses “97” and “111” Prefixes (Viper)
We have two different cores for this engine, depending on the year model. The 2002 and older blocks use a single bolt core, and the 2003 and later cores are a 3-bolt design. Big Block “B” or “RB”, Uses “21” and “23” Prefixes The “B” and “RB” engines used two different deck height blocks. They require different length pushrods, so when considering pushrod length, remember that the 383-400 engines use a shorter pushrod than the 413-440 engines. The larger engines with the taller blocks use a pushrod that is approximately 3/4” longer than the other.

When converting either of these engines to adjustable rocker arms, you must also replace the pushrods. The standard pushrod used with nonadjustable rocker arms uses a pushrod with a ball on each end. COMP Cams® aluminum roller rocker arms use a pushrod with a ball on the lifter end and a cup on the rocker arm end. The new COMP Cams® Pro Magnum Rocker Arm™ Kit for these engines uses a ball-ball pushrod like the standard setup, but the length is different. In either case, the correct pushrods must be used for the rocker arm type selected.

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Hemi, Uses “24” and “26” Prefixes
There are two basic factory versions of the original Hemi engine. The most common is the 426 Hemi, which was introduced in 1964. It uses the “24” prefix. Derivatives of this engine can be found in almost all Alcohol and Fuel cars racing today. One of the most popular drag racing engines, it is easily recognized by the distributor location, which is in the front of the block. As far as production engines are concerned, most of the parts are interchangeable. Hybrid Hemis; however, have relatively few interchangeable parts because most are custom made.

The old style 301-392 Hemi engine, which uses the “26” prefix, is most readily recognized by the location of the distributor at the rear of the block. There were several versions of this engine; therefore, it is highly recommended that before ordering any parts you make sure exactly which engine you are working on. These engines were very popular in the 60’s and 70’s and can still be found in many street machines and street rods, but they are becoming very hard to maintain due to the lack of replacement parts.

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General Tips

High Lift Cams
When changing to a higher than stock lift cam, several items must be checked to ensure long engine life and high performance. Spring coil bind, correct pressures, retainer to guide clearance and piston to valve clearance are just a few of the more common considerations. There is no exact formula to tell when you are getting into trouble, so to avoid serious problems, it is better to double check these things when installing a cam. If ever unsure, contact CAM HELP® at 1-800-999-0853.

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Springs
By far the most common problem encountered when installing a new high performance camshaft is the incompatibility of the existing valve springs to the new cam. Factory valve springs are designed to work with a certain lift cam, and since most aftermarket cams have higher lift, the springs must be addressed. It is highly recommended and a requirement of the warranty that the suggested springs be installed along with any COMP Cams® camshaft.

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Valve Stem Oil Seals
When changing to a higher than stock lift camshaft, it is common to have a clearance problem between the bottom of the spring retainer and the top of the valve stem oil seal. Before final assembly of the heads, install one seal, one valve and one retainer without the spring. Measure the distance between the top of the seal and the bottom of the retainer to be sure that it is greater than the lift of the valve by at least .050”-.060”. Be sure to take into account any extra lift due to higher ratio rocker arms.

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Flat Tappet Break-In
All flat tappet cams require special attention during the break-in process. Special springs and certainly tender loving care will be required to ensure long life of the cam. Please refer to the instructions in your cam box for complete procedures. If ever in doubt, please call the COMP Cams® CAM HELP® line at 1-800-999-0853.

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High Ratio Rocker Arms
A higher than standard ratio rocker arm moves the pushrod closer to the rocker arm shaft. It then becomes necessary to check

the clearance between the pushrod and the head where the pushrod passes through the head. This is a very common problem and should be checked when a rocker arm ratio change or pushrod diameter change is made.

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Rocker Arm Geometry
Proper rocker arm geometry is necessary to ensure the maximum benefit from any cam design. Camshaft base circle, block deck height, cylinder head design and lifter design all contribute to possible errors in geometry, which must be compensated for with pushrod length and shaft height. Usually, a longer than stock pushrod will be necessary in a high performance engine, but care must be taken to choose the correct length.

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Fuel Pump Pushrod
All Chrysler “B”, “RB” and Hemi engines use a fuel pump pushrod to actuate the fuel pump. The fuel pump must be removed and the rod dropped away from the cam prior to camshaft removal. Failure to do so will result in damage to the cam, pushrod or both.

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Rocker Arm Adjustment/Lifter Preload
All but a few Chrysler engines were equipped at the factory with non-adjustable rocker arms. Anytime a solid lifter camshaft (either roller or flat tappet) is used, you must also use the adjustable rocker arms and appropriate pushrods.

When installing any high performance hydraulic camshaft, the lifter preload is something which must be considered. Too little preload will result in a noisy valve train, and too much preload will result in tight valves and a poor running engine. Either condition can result in less than expected performance or engine failure. After the cam, lifters and rocker arms are installed and prior to installing the intake manifold, you must check the plunger depression in the lifter. With the cam on the base circle (valve closed) the plunger in the lifter should be depressed .040”-.060”. With nonadjustable rocker arms, you must change pushrod lengths to obtain proper lifter preload. This is a delicate and time consuming process, so if you have any questions, contact the CAM HELP® line at 1-800-999-0853.

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Rocker Arm Shafts
When installing the rocker arms on a shaft type system of a Chrysler engine, the shafts must be installed correctly. There is a difference in the top and the bottom, as well as side to side. The shafts must be installed with the oil holes pointed to the bottom and to the outside of the engine, toward the valve. This is the only way the shafts can adequately oil the rocker arms. Premature wear will result if the shafts are installed improperly.

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Lifters
The pushrod seat location is different in hydraulic and solid lifters in most applications. For this reason, pushrod length must be checked and may need to be changed when switching from solid to hydraulic camshafts.

When installing a roller cam and tappets into a Chrysler engine, you must be careful to ensure that the roller lifter sits in the lifter bore correctly. Most brands of roller lifters are designed with a cut-out in the lifter body around the lifter wheel. If this is installed toward the oil galley in the block, the result will be a loss of oil pressure and engine damage. COMP Cams® roller lifters do not incorporate this cut out, so there is no problem when using COMP Cams® lifters. When installing roller lifters in the block, remember to install the link bar side of the lifters to the cylinder side in small blocks and to the inside in big blocks and Hemis.

COMP Cams® produces a special lifter for oval track use in the “A” engines. This lifter is still the standard .904” diameter but is made to oil through the pushrod. This is for use in special highly modified blocks only and will not work in a standard block.

There are several different roller lifters listed for the Hemi engines. The only difference is the location of the pushrod seat.We have basically developed a drop-in replacement for most of the popular brand lifters available. Be sure to measure the height of the pushrod seat prior to ordering lifters.

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Lifter Bore/Oiling Modifications
Even though COMP Cams® roller lifters will work without oil system or lifter bore modifications, it is highly recommended that on any racing engine the lifter bores be modified. This will ensure that in the case of a pushrod failure and the lifter coming out of the bore, adequate oil pressure will be maintained. The proper procedure for this modification can be found in any of the materials available directly from Chrysler, or any top engine builder can perform this modification.

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Camshaft Journal Diameter
Many of the newer racing engines utilize a larger than standard cam bearing journal diameter. The advantages of the larger diameter are less flex and a larger base circle to smooth out the lobe design, making this a very desirable addition to any extreme racing engine. It is very common to use a 2.125” Ford babbit bearing in the Hemi engine. Some of the latest oval track blocks feature a roller bearing and require a 1.968” journal diameter. Make sure to specify journal size when ordering your cam. If no special size is requested, the standard journal will be chosen.

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Camshaft Cores/Timing Chains
On the big block “B” and “RB” engines there are two designs of the cam snout/upper timing sprocket where the cam is attached to the gear. The most common design is the single bolt type, which just means that the cam is attached to the timing chain with a single bolt. There is also the 3-bolt type, more common in high performance applications. These designs are totally inter-changeable, as long as the proper cam is used with the correct timing chain set. In any case, the 3-bolt design is the only style available for roller camshaft applications.

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Multi Groove Valves
No longer is it necessary to convert to “Chevrolet” style single groove valves to benefit from the superior strength of COMP Cams® machined steel 10º Super Locks™ and the variety of spring retainers available with this lock. Super Locks™ are now available for the multi groove Chrysler valves in both the 2 and 4 groove applications. They are available in pairs or in a kit with half 2 groove and half 4 groove locks. See page 311 for details.

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Lifter Bank Angles
The latest version of the “A” engine block features a different lifter bore angle. This block is commonly called the “R” block. The angle of the lifter bore is changed to help straighten out the pushrod angle. The standard lifter angle on the “A” engine is 57 degrees from vertical. This points the lifter away from the center of the block and angles the pushrod toward the outside. Most of the “R” blocks and some highly modified versions of the “A” engine have a 48 degree lifter angle. This points the lifter more directly at the rocker arm and helps to eliminate deflection at very high engine speeds. No standard production blocks were made with this modification, so if your block is not a special “race only” part from Chrysler, you probably have the 57 degree lifter angles. These cams are not interchangeable, so it is important to note the lifter bank angle prior to ordering any racing cam. If no special lifter bank angle is stated, the standard 57 degree cam will be used.

The same changes are common on some of the newer aluminum aftermarket Hemi blocks, the difference being much more subtle, from 45 to 48 degrees. It is extremely important to make sure which lifter angle your block is machined for prior to ordering a cam. As with the small block, if no special lifter angle is requested the cam will be ground as with the standard 45 degree lifter angle.

COMP Cams® has invested millions of dollars in Research and Development in order to stay years ahead of our competition. With today’s technology and brilliant minds working around the clock, COMP Cams® has rightfully earned respect as the leader in valve train technology in the automotive industry. Quality control is our main objective in creating award winning components, and the ADCOLE Model 911 is just one of the many machines we have invested in to maintain that quality. When you purchase any COMP Cams® valve train components, you make an investment into tomorrow’s leading edge technology in pursuit of ultimate power.

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