Mopar Small-Blocks. Larry Shepard

low end, similar to the 426 Hemi.

       Only two core plugs are installed per side in the aluminum block. There is also one large one in the front face. Notice that the center three mains are cross-bolted for maximum strength, similar to the 426 Hemi. Each center cap (number-2, -3, and -4) is cross-bolted similar to the 426 Hemi in Top Fuel. Therefore, it’s much stronger and stiffer than any four-bolt cap, but the cast-iron blocks do not have the skirt on the block for anchoring.

       The aluminum block uses steel main caps, and the center three are cross-bolted. Moreover, they use studs rather than bolts for greater strength. The unique front cover does not match the A-engine or Magnum engines.

Basic Features

      By about 2005, Mopar Performance offered more than 20 different blocks for the small-block. All were designed for racing; many options were available for virtually any engine project.

       The deck surface shows the sleeves pressed in each cylinder. The standard four-bolt small-block head bolt pattern sits around each bore with the added top and bottom bolts showing the six-bolt race pattern. The four-bolt head gaskets and four-bolt head works without the two extra bolts if that is desired. Note how far the tappet bores (48 degree) are from the centerline of the cylinders, even with the six-bolt in the tappet chamber.

       The aluminum block does not use either style of motor mounts and is designed for use with motor plates. The block is much lighter without all the motor-mount bosses.

      Mopar Performance Aluminum Block Features

       • Ductile iron dry cylinder liners

       • 48-degree tappet angle for almost ideal valvetrain geometry

       • Six-bolt head bolt pattern for superior head gasket sealing

       • Full skirted block design, similar to 426 Hemi for increased strength and rigidity

       • Cross-bolted main caps for added strength

       • High-strength A1 studs, bolts, etc.

       • 50-mm roller cam bearings designed to reduce friction

       A new block will come with new cam bearings but all others will have to have the cam bearings replaced. The block is upside down and the cam bearing oil hole is shown at the top and points down toward the main bearings. The oil holes in the bearing shell must line up with the holes machined into the block. In some cases you must use a small mirror to see if this is true.

       The standard water jacket extends down to just above the block’s pan rail. The core plugs are at the bottom of the water jacket. a threaded plug is also there that allows draining of the block. These threaded plugs are difficult to use after time. Installing a block drain allows you to drain the block fully and easily.

      Bore

      The amount of overbore depends on the block itself and when the block was built. Early 273 and 318 blocks (pre-1973–1974) can generally be overbored about .060 inch. Early 340 blocks can be overbored about .040 inch, or 4.080-inch actual bore size. The 360 is a gray area, but I use the 340 as a guide and limit overbore to .040 inch, or an actual bore size of 4.04 inches. All newer blocks, A-engines, and Magnums are thinwall casting designs, and overbore should be limited to .020 to .030 inch.

      All race blocks can be overbored more than production blocks. You can overbore the resto block to 4.08 inches with the siamesed-bore versions able to be overbored the most (approximately 4.22-inch max for the siamesed-bore versions). When pushing the boundary of bore size and overboring, it is best to sonic-test the block before you begin any boring operation.

       The main bulkheads must have enough material and strength to support four-bolt caps with vertical outers. Thus, there must be enough material between the main cap bolt of the two-bolt design and the outer wall below the pan rail. In this drawing, the dotted line represents the standard block casting. The solid line above it is closer to the performance blocks, such as the 340 T/A and the X and R block families. The vertical outer bolts break through in the standard casting. The main reason for splayed outer bolts is to put the bolt into solid material. This drawing is not to scale.

      Most race blocks are bored or rough bored to approximately 4.00 inches. There are many reasons to use a race block even if the bore size is less than 4.00 inches (such as the 318’s 3.91 inches). If you plan to race a small-bore engine, such as 3.91 inches or even 3.63 inches, you should not use the production block. It is a better package to use the race block with the proper-size sleeves.

      Mains

      The two basic main sizes are the 273/318/340 and 5.2L engines. The 360 and 5.9L use a larger main. The 360 has a large 3.00-inch main; the other group is small at 2.69 inches. The main cap bolt spacing on the 360/5.9L is also wider, or spread. Magnum engines have a small dowel that locates the number-5 main cap. Magnums also use smaller main cap bolts in the number-5 cap. Typically the main caps are made of high-nickel cast iron. If the main caps have been replaced or damaged, or if they bind during crank rotation, the mains should be align-bored, which is a machine shop operation.

      Height

      Most A-engine blocks were built at 9.60-inch block height; Magnum engines were built at 9.58 inches. Race blocks can be about 9.00- to 9.10-inch block height. Do not try to mill a production block to this height. Deck milling on production blocks should be limited to about .060 inch.

      You need to determine if the engine was rebuilt or repaired in the past and whether the block was decked .060 inch at that time. If the block has been decked by .060, the actual deck now is 9.54 inches. You should not take off another .060 inch because the deck becomes too thin and causes head gasket sealing problems that you will not be able to fix. This is one reason that it is so important to measure the block’s actual height before you start machining.

      Stroke

      The A-engine/Magnum engine can generally accept long-stroke cranks. Most of them use a 3.31-inch stroke; the 360/5.9L uses a longer 3.58-inch stroke. The performance aftermarket offers 4.00-inch strokes that are easy fits. Because the camshaft sits so high above the crank, long-strokes do not cause the connecting rods to hit the camshaft lobes. The pan rail and the bottom of the cylinder bore (pulling the skirt too far out the bottom) are still concerns with strokes longer than 4.00 inches.

       Oil routes from the pump to the oil filter on the side of the block, and then back into the block and up to the right side (next to cylinders-2, -4, -6, and -8) main oil feed galley. The right oil galley runs from the rear of the engine to the front, and it feeds down to the main bearings. As can be seen, the tappets are oiled directly since the tappet bores intersect with the galley. Then the oil goes up to the cam bearings.

Block Oiling

      A-engine and Magnum blocks oil in basically the same way. The difference comes in oiling the head and valvetrain. The A-engine oils the valvetrain and head through the head; Magnum engines