Standard Deck



Tall Deck

A Better Big Block

The classic Chevy big block production engine was introduced in 1965. In the late 1980s, a new version arrived, designed for marine and fuel-injected applications. The early engines are known as Mark IV big blocks while later blocks are Gen V and Gen VI. You can tell them at a glance by checking for a mechanical fuel pump mounting pad. If it has one, it's a Mark IV. If there's no fuel pump pad, it's a Gen V block.

Despite the fuel pump mounting pad difference in their castings, the cylinder blocks of the Mark IV and Gen V are based on the same design. There are several other differences, particularly in the water jackets near the deck surfaces, that make some Mark IV and Gen V parts incompatible (e.g. cylinder head gaskets).

Within the last few years, Chevrolet Performance revised the basic big block architecture to standardize the Mark IV and Gen V, creating an all-new cylinder block casting that combines the features of both generations. It also incorporates significant updates and strength-enhancing features that make the big block a stronger engine foundation with provisions to support 21st-century performance.

Although the basic big block architecture is revised, Chevrolet Performance continues to offer two versions, each differentiated by performance and displacement capability. The Bow Tie Block continues to be the block of maximum performance, and Chevrolet Performance crate engines use the revised big block design.

Here's what distinguishes the latest Chevrolet Performance Big Blocks from earlier castings:
  • Water jackets are revised near the deck surfaces so that Mark IV or Gen V head gaskets can be interchanged
  • Oil pressure feed holes are added to the oil filter boss and front bulkhead to support oil feeds for superchargers, turbochargers, etc.
  • Repositioned oil hole next to the camshaft bore at the front of the block enables safe machining of cam bore to accept 50mm roller bearing
  • A mechanical fuel pump mounting pad is included, similar to the Mark IV
  • A boss next to the distributor hole in the valley supports hardware for digital ignition equipment
  • A thicker, stronger front bulkhead has markings for 10-bolt timing covers (non Bow Tie blocks have 6 holes; remaining holes must be drilled)
  • Non Bow Tie blocks are machined for 4-bolt parallel main caps; Bow Tie blocks are machined for 4-bolt splayed caps
  • Revised rear-of-block allowed for the machining of 1-piece or 2-piece main seals (similar to Gen V design)
  • A front clutch boss is included for older muscle car applications
  • 454 blocks have a slightly beefier main web than previous blocks
  • All blocks are made with the standard production roller camshaft and lifter machining
  • 502 and Bow Tie blocks share the same main web, which is considerably stronger than the Mark IV and first generation Gen V Bow Tie block
  • Bow Tie blocks have a unique water jacket to allow up to 4.600'' bores (these blocks can be identified by a ''B'' suffix in the casting number)
  • Two additional core plugs are in the rear bulkhead (they enhance the manufacturing process at the foundry and help improve overall quality)
  • A Bow Tie logo and other identifying marks are incorporated on Bow Tie blocks to differentiate from previous generations