Chrysler Hemi-6 Engine

The Chrysler Hemi-6 engine is a family of inline six-cylinder petrol engines produced by Chrysler Australia in three piston displacements and multiple configurations. Hemi-6 engines were installed in Australian-market Chrysler Valiants from 1970 through 1981. It was also installed in the Valiants closely related variants, the Chrysler VIP, the Chrysler by Chrysler & the Valiant Charger.

Chrysler Corporation in the US had been working since 1966 on an inline 6-cylinder engine, called the D-engine, to replace the Slant 6 (G-engine) in Dodge trucks, but abandoned the effort after prototypes were built. This was Chrysler's first thin wall (lightweight) cast iron engine design. Chrysler Australia wanted a new six-cylinder engine for use in the Australian Chrysler Valiant, and so Chrysler USA sent a prototype engine to Chrysler Australia's engineers to continue developing the D-engine. The first 245 cu in (4.0 L) variant was released for the 1970 model year in the VG-model Valiant.

In a major coup for the company, Chrysler Australia's ad agency, the Young & Rubicam Advertising Agency in Adelaide, South Australia, secured the services of British racing driver Stirling Moss to promote the new Hemi-6 4.0 L (245 cu in) in 1969. The agency managed to fly Moss to Adelaide in secret for the advertising campaign, surprising Chrysler Australia's executives. Young & Rubicam's parent company were also the advertising agents for the Chrysler Corporation in the US.

The Hemi-6 is a pushrod O.H.V. (overhead valve engine), with combustion chambers comprising about 35% of the top of the globe. This creates what is known as a low hemispherical shaped chamber. In this way, the "Hemi" moniker was used for the same kind of marketing cachet as Chrysler's 1950s-1970s Hemi V8 engines.

The Hemi-6 valves are angled apart (splayed) 18 degrees (included angle) along the crankshaft axis, and the intake valves are as large as 1.96 in (50 mm). The 6 intake and 6 exhaust valves open slightly towards each other and away from the cylinder wall, which results in less "shrouding" of the valves and greater airflow potential. In addition, both valves are slightly inclined across the crankshaft axis, similar to a conventional "wedge" chamber. The cylinder head is not a crossflow design, meaning the 6 intake and 6 exhaust ports are on the same side of the engine (the left, Australian and British passenger, side).

Unlike Chrysler's contemporaneous hemi V8 engines, the Hemi-6's rocker arms are mounted on individual studs (similar to the Chevrolet "big block" V8), rather than on 2 separate rocker shafts as in all 1951-58 Hemis—Dodge, DeSoto, Imperial, and Chrysler "Firepower" and 1964-'71 Plymouth and Dodge 426 V8s.

All Hemi-6s share a robust crankshaft supported by seven main bearings, and this family of engines quickly developed a reputation for excellent performance, economy, and durability.

The Australian Hemi engines were designed by a five-man team which included the late Maurice Harcus.