Mopar Small-Blocks. Larry Shepard

Vibration Dampeners

      The basic dampener design has a steel/cast iron outer ring that is mounted to the hub by a rubber isolator (thin strip). As the engine vibrates, the outer ring absorbs these vibrations and basically cancels them out. You should always select a vibration dampener suited for the specific engine, in this case a Mopar A or Magnum. Although not required, SFI dampeners are best; these include versions from ATI, TCI, or BHJ.

      I recommend staying away from aluminum dampeners (solid) or any one-piece dampeners. If an SFI dampener is not available for your engine, stick with the production dampener for street use. A street engine or street/strip engine must have a dampener, and many options are available. Any street/strip manual transmission should have an SFI dampener, and any engine using 7,000 rpm or higher should have an SFI dampener. The leading manufacturers are ATI, TCI, BHJ, Pro/Race, and Fluidampr. Each unit is unique.

      Race engines need lightweight dampeners, but street or street/strip engines do not require a low-mass dampener. The TCI Rattler weighs just over 8 pounds and features a unique construction.

      The Pro/Race offerings are more traditional with a steel outer ring construction and a production-type weight of more than 11 pounds.

      The BHJ dampener is also built with the outer-ring-style construction (similar to production) and weighs just under 8 pounds with a combo option at just over 6 pounds.

      ATI has the most models that feature two or three discs/rings mounted inside of a shell. The shell can be made of steel (8.75 pounds) or aluminum (6.25 pounds). Both are three-ring versions plus there are two-ring versions at 7 and 5.45 pounds, respectively. I do not recommend the two-ring versions for street use.

      The Fluidampr is distinctly different from others and is around the production weight.

      Dampeners need to be tuned for specific engine hardware: stroke, engine RPM, etc. I feel the Fluidampr is best for non-standard engine hardware, unique stroke length, or unique cubic inches, etc. Several dampener manufacturers solve the external balance issues of the 360 and 5.9L engines (they are not the same) by adding small weights in the hub area.

      The non-symmetrical 360 dampener is basically round but has an offset weight. The weight is placed in the wide flange on the front of the dampener, which only extends for about 200 to 250 degrees, or in a trough cast into the front face of the outer ring for less than 180 degrees.

      These non-symmetrical dampeners are also somewhat thicker than the standard 318/340 dampener. The original 5.9L Magnum used a dampener similar to that of the 5.2L. Newer versions used a large, one-piece dampener and front pulley.

       The 318 dampener (on the right) is symmetrical; basically a round disc. There is the timing mark on the outer ring and the six bolts that allow the front pulley to be attached. The 273 and 340 forged crank dampeners are basically the same as the 318. The original Magnum 5.2L engines used a similar dampener but newer versions went to a one-piece dampener and front pulley assembly, which is very heavy and difficult to work with. The 360 external balance dampener is on the left with the weight added toward the top of the dampener.

       The 360/5.9 external balance dampener can have the external weight removed from the opposite-side weight (see page 33). The trough in the face of the dampener from about one o’clock to about seven o’clock removes weight that balances the engine just like adding weight to the dampener at four o’clock.

Connecting Rods

      The connecting rods are a critical part of the rotating assembly. The rod’s weight (in grams), material (steel, titanium or aluminum), alloy (forged steel or high-carbon steel for the steel versions), style (I- or H-beam), and pin retention (pressed or floating) are all important.

      Production Versions

      There is not much to pick from in the production small-block connecting rod area because they are all made of forged steel and are 6.123 inches long. The tricks come with the 318 rod being lighter and the 340 rod having a bushing in the small end to accept a floating pin. All production rods use 3/8-inch bolts and nuts to attach the cap to the rod’s beam.

       All race dampeners are SFI-approved and these dampeners can be used on externally balanced engines. Race dampeners were made much lighter, but lighter weight tends to place more stress on bearings. In some very popular engine packages, the manufacturers actually develop (or tune) the dampener to the specific engine package and RPM range that the engine is currently using.

      For high-performance applications, use ARP bolts in place of the stock rod bolts in any production rod. With good bolts, the stock rod is fine. High RPM will cause problems for pressed pins, but stock rods typically hold up well.

      Aftermarket High-Performance Rods

      Selecting the correct connecting rod is one of the most important decisions you make when building your engine. Mopar connecting rods are offered in I- and H-beam design and in forged or billet constructions. Cast rods (not used in Mopar small-blocks) are adequate for base high-performance street engines up to 500 hp, but beyond that you need to consider a forged connecting rod. Billet rods are typically used for 800-hp race builds. Aluminum rods are also forged and are used on supercharged engines but not required in the street/strip versions. They are limited to race engines. Another player is titanium, but these are also race-only parts.

       Connecting rods are detailed parts. Because all production rods have the same length (6.123 inches) you can use the forging number for identification or you can weigh the assembly and compare weights.

      For engines built to rev more than 7,500 rpm, I recommend a high-performance rod from Eagle, Scat, K1, Carrillo, or Manley. You must not mix and match rods; they need to be installed as sets. My first choice is the 585-g Scat I-beam with 7/16-inch bolts and cap screws; it provides adequate strength for any street/strip build package. All production rods use 3/8-inch bolts, except K1 rods, which use 7/16-inch bolts for greater strength. However, these bolts add weight to the rod assembly.

      In some cases, the I-beam rod is slightly lighter than the race-designed H-beam style. The Eagle I-beam rod weighs 605 grams; the H-beam version weighs 680 grams. The standard Manley I-beam rod weighs 555 grams but is limited to 550 hp; the “Pro” I-beam rod (a heavier forging) weighs 670 grams and is rated at 700 hp.

      Note: Only the 340 used floating pins. Connecting rod weights: big end, 500 grams; small end, 226 grams.

       When mounted to the connecting rod, the piston must have clearance between the two-piston pin towers (one on each side). This production-based piston has 1/4 inch on each side. With performance or racing pistons, this clearance tends to get much smaller and, in some cases, may have to be checked. This is not really required for production or service packages. Note the round hole in each pin tower for pin oiling. Each manufacturer uses a different method to oil the pins.

       The big end of the rod holds the rod bearing shells and bolts hold the cap on to the beam, which in turn holds the rod to the crank. The key to all of that happening correctly is the rod bolt and nut (toward left). Production-based rods