When it comes to Chevrolet’s high-revving 302 small-blocks, there is no shortage of information, speculation, and even myths. The Chevy 302 was never a mass-produced engine like the 350, and its short run from 1967 to 1969 has left enthusiasts sorting through decades of details. What follows is our best knowledge about how these engines were coded, cast, and produced during that three-year stretch.

1967: The First Year 302

The 302 made its debut in 1967 as Chevrolet’s answer to SCCA Trans-Am rules, which limited displacement to 305 cubic inches. Engineers combined the 4-inch bore of the 327 with the 3-inch stroke of the 283 to create a high-revving package that was perfect for road racing.

For this first year, the 302 used a small-journal block with 2.30-inch mains. The engine suffix codes were MO for the standard version and MP for engines equipped with the A.I.R. emissions system. The correct casting number for these blocks is 3892657. These small-journal engines are the rarest of the 302 family, and their uniqueness makes them highly desirable among collectors today.

1968: The Switch To Large-Journal

In 1968, Chevrolet updated its small-block lineup with large-journal mains for added durability. The Chevy 302 followed suit. The suffix code remained MO, which sometimes causes confusion with the previous year’s small-journal version. The new block carried the casting number 3914678 and featured the stronger 2.45-inch journals.

Internally, the recipe stayed much the same, but the large-journal crank improved the engine’s ability to survive at the high rpm levels that Trans-Am racing demanded. For enthusiasts chasing authenticity, this detail is critical: a 1967 MO engine is not the same as a 1968 MO engine, even though the suffix is identical.

1969: The Famous DZ302

The 1969 model year is when the Chevy 302 truly became a legend. This was the first year Chevrolet used the DZ suffix code, a marking that collectors now instantly recognize. Several block casting numbers are correct for this year, including 3932386, 3956618, 3932388, and 3970010. All were large-journal designs.

The ’69 version also benefited from refinements in internals and remains the most widely known and collectible of all 302s. When enthusiasts refer to “the DZ302,” this is the engine they mean: a purpose-built, high-revving small-block designed to win races and sell Z/28 Camaros.

Sorting Fact From Fiction

Like many small-block Chevys, verifying a true 302 can be tricky. Blocks look similar, casting numbers were shared across different displacements, and pad stampings can be faked. That is why collectors put so much emphasis on the combination of casting numbers, suffix codes, and internal measurements.

There is a lot of information out there about these engines, and not all of it is consistent. What we have laid out here reflects the most reliable knowledge about Chevrolet’s 302 program from 1967 through 1969. Whether small-journal or large-journal, MO or DZ, these engines remain some of the most interesting and sought-after small-block Chevrolet ever built.