340 oil pan’s front and rear sealing surfaces are the same as the 318’s; the 360’s are smaller.
The 1970 340 T/A is the trick block for racing applications because it has thick bulkheads on the number-2, -3, and -4 main bearing bulkheads. The added thickness allows for vertical four-bolt main caps to be added to these center mains. None of the Magnum blocks have this thick bulkhead. In the mid-1970s, Chrysler offered a four-bolt main race block known as the X-block (it had a large “X” on the passenger-side front wall of the casting). In the mid-1990s, Mopar Performance and Chrysler revised this race block and offered the R1 through R4 race blocks. These were generally called the R-blocks and all featured four-bolt mains.
When you are selecting a block for your particular build, remember that for all five of my performance packages, the standard 340/360 or Magnum block can be used as long as the bore size is limited to .020/.030 overbore for the last two packages. An R-block is not required as long as the blocks are limited in overbore. If a big-bore engine is desired, an R-block is required, and the siamesed-bore version allows the largest bores. The 340 resto block is a version of the R-block. If your 340 or 360 block is already overbored too far, sleeve the bore back to 4.020 inches (360) or 4.04 inches (340).
The 340 T/A block is very difficult to find; it’s even more difficult to find someone willing to give one up for a performance project. The 340 resto block, by Mopar Performance, is more readily available. It uses the 340 T/A casting number and the 340 displacement number after it, followed by an “M,” all the way to the right after “340.”
The 318/5.2L and the 360/5.9L are the two groups of small-blocks. You can identify them easily by quickly looking at the core plugs located in the sides of the blocks. There are three in each side. In the 340 and 360/5.9L group, the core plugs line up with the three center bulkheads, and if the plugs are removed, you can see the water-jacket gap between adjacent cylinders.
On the 318 and 5.2L blocks, the core plugs are spaced farther apart and don’t line up with the bulkheads, except the center one is close to the number-3 main. The R-block will support the most power, then the X-blocks and then the T/A and then all stock blocks. Magnum blocks are slightly stronger than the standard A-engine blocks. The stock blocks with 0 to .020/.030 overbore have done over 550 with no problem (good bolts and good main caps) but the upper limit is unknown. Most members of the 700-hp club use some version of the race block. The race blocks make more horsepower.
Around 2000, Mopar Performance started offering a 340 restoration block that not only had the thick bulkheads of the 1970 T/A block, but also had actual four-bolt mains on the center three mains. It used the same casting number as the original 340 T/A with a 340-M added, but the siamesed-bore block is no longer offered. This stout non-siamesed bore block can support at least 1,000 hp, but availability is limited. The R3 race block is an excellent block for 700-hp street builds, but these can be expensive and difficult to obtain so other choices are offered.
The large round hole with a plug in the center is the cam’s rear plug. The threaded square-drive plugs on either side of the cam plug are the oil galley plugs. These allow the oil galleys to be drilled and then sealed. The main oil feed galley is the one on the right.
The 318 Magnum block is tipped over to the driver’s side so the passenger-side deck is horizontal. The oil galley plugs are in the middle toward the bottom. The distributor bore is at the left and the china wall runs up toward the right from the large distributor bore. The rear intake gasket seal is just ahead of this surface. At the upper end of this machined surface is another oil hole typically used for oil pressure senders. It is important to know where this hole 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
