The Sigma engine family began life with the simple V6 name.

The G6AU and G6CU (both also called the 3.5 D ) are the large 3,497 cc (3.5 L; 213.4 cu in) versions of the Sigma engine.

The 3.5 D has a cast iron engine block and aluminum DOHC cylinder heads.

It uses Multi-port fuel injection, has 4 valves per cylinder, and features forged steel connecting rods.

It is designed to run on "regular" unleaded gasoline rather than the premium fuel used in many other high-output V6 engines.