Mopar Small-Blocks. Larry Shepard
is for future discussions in this chapter.
The bare front face of the block has lots of holes. The core plugs are the two at the bottom; one is on the right while the other is on the left. At the top right and left are the block’s two water feed holes. The cam bore is in the center. The oil galley holes are on each side of the cam bore. The cam retainer is attached by the four smaller holes: two below and two above. The two larger holes above the cam retainer attaching bolt holes are vents from the tappet chamber to the front cover.
With the main bearing shell removed, you can see the two oil passages intersect just above the hole. The white welding rod is in the main oil feed from the main oil galley (hole to the right of the cam plug hole). The oil comes from the main oil galley down to the main bearings and then up to the camshaft through this Junction.
Race Blocks
The original race block for Mopar small-blocks was the 340 T/A in 1970. It was produced for only one year. When NASCAR began handicapping the big-blocks, both Hemi-head and wedge-head designs in the early 1970s, the NASCAR teams began using the T/A blocks, but they had to remove them from actual Trans-Am cars. This was a lot of extra work! To solve this problem, Chrysler introduced the X-block, which had all the features of the T/A block plus a few more. This X-block was readily available to racers and was very successful.
When the government issued the loan guarantee to keep Chrysler operating, the X-block tooling was lost during the confusion it created. In the late 1980s, the demand for a race block began to build, so Mopar Performance introduced the new “R1” block, which replaced the X-block. Then came the R2, R3, and R4. Each one has its name cast into the passenger-side front wall of the block.
Block Height Calculation
The block height, or deck height, is defined as the distance from the center of the crankshaft to the top of the block’s deck surface, measured along the cylinder bore’s centerline. The small-block Mopar’s production block height is 9.58 to 9.60 inches, but blocks are commonly milled or decked at each rebuild, so do not depend on this number as an absolute. You don’t always know the block’s history. However, you can calculate the block height using the following simple equation:
BH = S ÷ 2 + RL + CH + DH
Where:
BH = block height
S = stroke
RL = rod length, center to center
CH = compression height of piston, measured on the actual piston
DH = deck height of piston, measured in the actual block
For example, on a 318 (or 5.2L) engine, the stroke is 3.31 inches, rod length is 6.123 inches, stock piston’s compression height is 1.74 inches, and the piston’s deck height is .082 inch below the 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