426 Hemi

1964-65 Race only, 1966-71 Street version • 4.25" bore x 3.75" stroke
How do you spell the ultimate in production performance engines? H-E-M-I. The mighty 426 Hemi was conceived in the early '60s as the ultimate race engine, and ended up being the top powerplant of the muscle car era. But we're getting ahead of ourselves.

The story of the street Hemi actually starts in 1963, when Chevrolet set a new track record at Daytona with their Mark II "Mystery Motor", the forerunner to the Mark IV big block. The Chevrolets broke during the race, which led to a Ford sweep in the biggest race of the year. Now, at Chrysler, the handwriting was on the wall. Get competitive or get out. So the Race Hemi was created by taking the early Hemi heads and adapting them for use on the RB bottom end.

The mighty 426 race Hemi was ready for the '64 race, where Chrysler finished 1-2-3. The engine was a stunning success -- too much so in fact. Bill France, the Supreme Ruler of NASCAR, decreed that only production engines could be campaigned on his circuit. As a result, Chrysler boycotted the '65 season but they would return.

In 1966, the Street Hemi was born. With the engine now in production, the Hemi could be raced in NASCAR legally. The street version of the Hemi is surprisingly similar to the race-only version, with only minor changes made for civility. The compression ratio was lowered to a more livable 10.25:1. The radical cross ram manifold and lumpy cam didn't make it either, but the street version did receive two 4-bbl carbs (mounted inline) and a solid-lifter cam big enough to churn out 425 horsepower (which was substantially underrated). The valvetrain was essentially the same as the race units, although the valve springs were replaced with much softer units to keep cam wear to a minimum. The factory developed a set of cast-iron exhaust manifolds to replace the racing headers, which reduced noise and increased durability.

In street form the 426 Hemi became known as the top-dog muscle car powerplant until it disappeared after the 1971 model year (which, by the way, was also the last year for the 440 6-bbl). The Hemi did undergo a few running changes through its production life, with the most noticeable being the camshaft and block change in 1970. The mechanical cam was replaced with a hydraulic type, and the block was revised and strengthened also, basically making it suitable for use in fuel (nitro) drag racing. The rest, as they say, is history.

Civilizing a race engine for street use requires some innovative engineering. Since the 426 Hemi head was designed for competition use only, no provisions for carburetor heat were included. Chrysler engineers provided heat to the carb by running tubes from the passenger-side exhaust manifold to the back of the intake.