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Hemi Engines - Great American Engines

The New Generation Hemi

Photography by Courtesy Of Chrysler Group

Oldsmobile and Cadillac had already made it to market with overhead-valve V-8s by the dawn of the '50s, but in 1951 Chrysler introduced an amazing engine-the Hemi V-8. The new engine was based around combustion chamber technology that had been partially developed during the war for aircraft and tank engines. The core of this architecture was the hemispherical-shaped combustion chambers that placed the valves in a stacked configuration at opposing angles. This design increased the efficiency of combustion and allowed for bigger valves, centrally located spark plugs, and more direct routing of the intake ports. By the time the Hemi made it to production for the '51 Chryslers, it sported 331 ci and compression that cranked out an astounding-for-the-day 180 hp.

Of course, the rest is not simply history, but legend. The Chrysler Hemi was a force to be reckoned with at any dragstrip in the country by the late '50s, and served as the basis for the earliest Top Fuel engines. Later, in the mid-'60s, Chrysler raised the bar it had set by creating the 426 Hemi, first in race form and later as the infamous Street Hemi. This engine set standards in drag racing, stock car racing, and on streets across America. Sadly, combined forces conspired to kill the Hemi in the early '70s, and while it remained the standard for Top Fuel, it became a part of the U.S. auto industry's incredible past-a time even the most optimistic motorheads knew would never return.

In 2004, the landscape of the auto industry is again changing, and once again, technology-and the resulting power output it yields-is a factor that the motoring press and public hold in high regard. This latest competition has driven automakers-both domestic and foreign-to rethink the automobile and the engines that power them, and DaimlerChrysler is making a strong showing. As the new millennium rolled in, the Chrysler Group introduced one of its first completely new V-8 engines in decades, though at 4.7 L and sporting single overhead camshafts, it seemed quite similar to Ford's 4.6 SOHC engines, which had yet to truly impress. In fact, the 4.7 proved a worthy replacement to the familiar 318, but then the Chrysler Group shocked the industry by introducing yet another completely new engine, and an honest-to-God Hemi at that.

The all-new Hemi uses a cast-iron, cross-bolted block topped with aluminum dual-plug cylinder heads and fuel-injection, which would have made it sound like an exotic racing engine back in the days of the last production Hemi. There's been some debate over whether the Hemi is a true Hemi, since the chambers include two small shelves or quench areas that improve mixture motion and combustion efficiency. Nitpicking as that may be, today's version displaces 5.7 L (about 345 ci) and runs 9.6:1 compression, and while this might sound a bit pedestrian to '60s Hemi aficionados, it's good enough to generate 345 net horsepower (1 hp-per-cubic-inch). Plus, since this initial offering is intended for trucks, you can likely expect future versions to pump the power level up.

Other than the name and the idea of a hemispherical combustion chamber, the new Hemi shares almost nothing with its ancestors, though the familiar broad valve covers are present, and they still contain a pair of rocker shafts. The new engine's cylinder heads had to be trimmed down in dimensions so that the engine would drop into modern engine bays, and one result was that the angle between the two valves is 34.5 degrees rather than the Street Hemi's 58.5. However, this is actually more of a benefit than a compromise, as the roof of the combustion chamber is shallower as a result, requiring a smaller dome on the pistons, which allows for better flame-front propagation and cleaner emissions output.

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