The original 265-cubic-inch small-block may have gone out of production after only two years, but it made a huge impact in that time. Engineered by Ed Cole and Zora Arkus-Duntov in a mere 15 weeks in 1955, the 265 was intended from the outset as a replacement for the old "Stovebolt Six" and then used in the Corvette. The 265's overhead-valve heads used 1.72-inch intake valves and 1.50-inch exhaust valves, a trait carried over to the 283 in 1957. The 265's heads lived on in the 283 through 1967, with the only major change being a switch to 1.72-inch intake valves.
In many ways, the story of Chevrolet's evergreen small-block is the story not just of the American auto industry but of an entire generation. Conceived by hot-rodders, for hot-rodders, the small-block has endured everything from the Dark Ages of America's smog years to fuel injection, and even its own demise in 2003. And all of that started way back in 1955, when an engineer named Zora decided to apply the best in aftermarket head technologies to an otherwise straightforward V-8.
The First Heads: The 265 and 283
The 327 and 302
While the original 327 and 350s used dozens of different head castings, the first and most basic 327 castings were essentially just 283 castings. The 327 got several of its own castings during its second model year in 1962, but ultimately wound up sharing its best one with the high-revving 302. This is where the Chevy heads' performance really began to take off, with larger 1.94 and then 2.02-inch intake and 1.60-inch exhaust valves. This is where we see the famous "double hump" heads with 64 cc combustion chambers, originally designed for dual-quad and fuel-injected Corvettes but eventually adopted for high-performance 350 engines.
Original 350 and 400 Heads
While the 302 hung on until 1969, it was largely superseded by the 350 in 1967. The 350 was essentially a super-sized 327, so it should come as no surprise that it originally used heads designed for the 327. But that's no bad thing, since these 327/350 castings were some of the best produced all the way through the modern era. The 400, introduced in 1970, got something of a raw deal in terms of heads primarily because it showed up right before the emissions Dark Ages. Things looked pretty dim from 1973 through 1985, until a ray of light showed up in the form of Chevrolet's aluminum L98 Corvette head; the first purpose-built, high-performance head casting since Chevy's musclecar heyday.
Performance Castings and the LT Engine
While the L98 would live on to become the GM Performance ZZ4, the real revolution happened with 1992's dual overhead cam LT5 head. Intended solely for the Corvette ZR-1, these beasts remain the stuff of legends and are about as rare as talking Loch Ness monsters. While it only lasted through 1995, many of the LT5's design features went into the LT-series -- Vortec -- heads that would later come to be regarded as some of the best factory castings ever. Like all legends, the traditional small-block Chevy bowed out after its greatest incarnation: the LT4. The LT4 head was the first and last real re-design of the traditional small-block head, with the fully modern ports and combustion chambers that make it such a popular swap item more than a decade after its introduction.
- How to Build and Modify Chevrolet Small-Block V-8: Cylinder Heads; David Vizard
- How to Port and Flow Test Cylinder Heads; David Vizard
- Out in the Shop: Chevy Head Casting Numbers
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