deck. Using the formula, you find that block height is 9.6 inches (1.655 + 6.123 + 1.74 + .082).
If this engine’s deck height measures .062 inch (instead of .082 inch), it indicates that the block has been decked .020 inch.
Deck height is often confusing because it sounds similar to block height. However, it is defined as the distance from the top (flat) of the piston at top dead center (TDC) to the top of the block’s deck surface. Typically, it is measured with a dial indicator or a bridge, which includes a dial indicator. If you have a dished or domed piston, the top of the piston is the flat part at the outside edge that is not part of the dome or dish.
This drawing shows the relationship of the various block specs required for the block height calculation. The key spec is the piston’s deck height because it is used in the compression ratio calculation, which is very important for max-performance engines.
The standard production small-block tappet angle is 59 degrees (shown), but the R-block family has the capability for using 48-degree tappets. The 48-degree angle was selected based on installing a race W cylinder head and race adjustable rocker arm onto the block (in the computer) and drawing a straight line from the center of the camshaft to the center of the rocker’s pushrod pivot. The resulting tappet angle was 48 degrees. While the R-block casting is made to use both the tappet angles, once the block is machined for one tappet angle, it can’t be converted to the other tappet angle!
Some of these R-blocks are cast with siamesed-bores, which means that the bore walls of adjoining cylinder bores are merged together, with no gap. This siamesed situation exists at three places per side (cylinder bank). This siamesed-bore alignment generally allows the actual cylinder bores to be larger because there is no water-jacket between the cylinders.
R-blocks can be converted to a six-bolt cylinder head by adding two more head bolts to the stock four-bolt pattern. This is a critical upgrade for super-high compression ratios, such as 13:1. A study showed that four-bolt heads were bending the head over the gasket’s sealing ring. The two extra head bolts keep the gasket material farther away from the bore. The bolts and gasket support help maintain a flat deck surface with high clamping loads.
The 59-degree tappets are so close to the tappet wall that the wall has a relief machined in for each tappet/pushrod on the Magnum blocks. The 48-degree tappet blocks have the tappet bosses much farther away from the tappet wall with no reliefs required.
Magnum tappet bores are machined at the top to provide space for the yoke to sit around the hydraulic roller tappets. The yoke sits in the relief and is held in place by the spider.
One boss was added straight up in the tappet chamber and one was added straight down on the outside of the block. In some cases these bosses are left unmachined or are machined off if not desired. If they are machined, they do not have to be used. If you use them, you must use a six-bolt–style head gasket. All of these race blocks (X and R versions) are cast-iron blocks made with high-nickel-alloy cast iron.
Most LA-engine small-blocks were built at the Mound Road Engine plant in Detroit, then added to the Windsor engine plant in Canada, and later the Toluca plant in Mexico. Many A-engine blocks were cast at Chrysler’s Indianapolis, Indiana, foundry, which was closely involved in the early stages of the R-family of blocks.
Aluminum Blocks
Mopar Performance began offering aluminum small-blocks designed for racing in the early 1990s. They are designed and built for the serious Sprint Car and drag racer who competes in classes that allow aluminum blocks. The latest version weighs approximately 95 to 100 pounds, a weight savings of more than 25 pounds over the previous version. These blocks were offered in two basic deck heights, 9.00/9.10 and 9.56 inches. They are shipped with one of several options in bore size.
The Mopar aluminum small-block shown comes in basic deck heights: stock-style height of 9.56 inches and the short-deck version at 9.00 inches; it can support more than 1,000 hp. The block features a fully skirted 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.
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
