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- 340 Replacement Block
- Siamese Bore Casting
- Casting # P5153477
- Works with Most Stock Style Small Block Parts (1964-1992)
- Cam Bearings Installed - Stock OEM Style
- Bore - Honed to Stock 340 Size 4.040"
340 Replacement blocks are designed for general HP use and entry level racing. These blocks are a heavy duty "LA" 340 block that will work with mostly stock style engine components (i.e. 1968-1973 340 & most other "LA" 318/360 parts - up to 1992). These blocks will not work with the production style 1987-1992 LA 318/360 hydraulic roller tappet camshaft & tappets w/ dog bone. These blocks come w/ the stock bore size for a 340 and are honed to size for use with stock pistons (except where noted). There are two versions of this block, one version is the Siamese bore (P5153478AB) & (P5153743), and the other has a full water jacket (P5007552AB).
These blocks are made from high strength cast iron and are heavy-duty pieces with extra stock for improved strength. All of the blocks include 4-bolt main caps on the center 3 caps (with ARP main cap bolts). Most of the blocks come with a Siamese bore water jacket and some have the full water jacket. The 48° tappet bore blocks come with a 6-bolt cylinder head bolt pattern. The 59° blocks have a 4-bolt pattern for the cylinder head.
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This package includes the engine block assembly with main caps, main cap fasteners, and the block hardware kit. Some of the block hardware is installed in the block and some is included in a separate package with the block.
The R3 and R4 blocks are designed for use in racing where the engine builder does most of the final machine work (i.e. boring, honing, and camshaft bearing installation).
For builders who demand rugged durability, simple reliability, and a foundation that can handle serious power, the Mopar Performance Cast Iron Engine Blocks & Components in the small block lineup are the go-to choice. These cast iron blocks are built with race-proven strength, ready to take abuse in drag strip, circle track, or heavy-duty street applications.
Among the options is the legendary mopar r3 block—a cast iron race block designed with four-bolt mains on the center three caps, thick walls, and extra material in key areas for strength. Deck heights vary depending on your build goals, including shorter decks for dry-sump setups and tall decks for big-inch displacement, letting you tailor your build for RPM, torque, or compliance with class rules.
If you're actively shopping, you’ll see a number of mopar r3 block for sale that come in different combinations of tappet angles (48-degree or 59-degree), with either Siamese or full water jackets, and with machined features compatible with LA-style or Magnum motor mounts. These blocks often accept many stock components, which helps keep your build budget under control without compromising on toughness.
And of course, the storied 340 block is part of this ecosystem—offering a tried-and-true parts pool and interchangeability with many of your favorite Mopar small block components. Whether you want a cast block for high output or a replacement block for reliability and street use, these Mopar Performance cast iron small blocks deliver value, strength, and flexibility. Ready to start? The right block here sets the foundation for the rest of your engine build.
