Continued from Chevrolet pt.1

The 1963 Z-11 427 was a heavily modified member of the 348/409 engine family. It was factory-rated at 430 horsepower.

It’s important to realize the importance certain manufacturers, most notably Chevrolet, Pontiac, Chrysler and Ford, placed on the emerging racing series in the early ‘60s. NASCAR and the NHRA were beginning to drive much of the performance development undertaken by Chevrolet. What this means is that once things heated up, new combinations appeared with amazing frequency. An example is the top-level performance 409 engine that made 360 horsepower in 1961, 380 in 1962, and a stout 425 in 1963. Also in 1963 Chevrolet released the Z-11 option which included a special 427 cubic inch “409” that made a conservatively rated 430 horsepower. This was truly a unique engine in that the Z-11 used a two-piece intake manifold with the lower valley cover being separate from the upper runners. This engine also featured two Carter 4-bbl carburetors, big-valve (2.19”, 1.72”) heads and a mechanical camshaft featuring .556” int/exh lift and 325° int/exh duration. Even though only 55 or so Z-11 cars were produced, this undoubtedly represents the zenith of W-engine development.

While the W-engines were holding their own on the streets and race tracks of America, Chevrolet realized they were close to the limits of the engine. Therefore, again in 1963, Chevrolet showed up at the Daytona SpeedWeeks with a completely new big-block engine design. Press-types, having never before seen this engine, dubbed it the “Mystery Motor”. Chevrolet called it the Mark II engine. Competitors called it unfair and a host of other things unsuitable for print in a family magazine. This was, of course, the forerunner to the familiar Mark IV big-block engine.

The Mk. II "Mystery Motor" of 1963 was the father of the Mk. IV big-block engine family.

The most notable feature of the Mark II engine lay in its cylinder heads. The engine was a “semi-hemi”, meaning the intake and exhaust valves were not only offset toward their respective ports, but also splayed or canted toward the center of the cylinder. This greatly enhances breathing, particularly at high valve lifts and high engine speeds