The 426 Hemi, in "street Hemi" form, was produced for consumer automobiles from 1965 through 1971. To avoid confusion with earlier (1951'58) and current Hemi engines, the 426-based Hemi is sometimes called the "2G" or "Gen 2" Hemi.
The Boss 429 Mustang (also known as the "Boss 9" by enthusiasts) is arguably one of the rarest and most valued muscle cars to date. The Boss 429 engine was derived from the Ford 385 engine. It used four-bolt mains, a forged steel crank and forged steel connecting rods. The engine featured aluminum cylinder heads, with a modified Hemi type combustion chamber which Ford called "crescent". These heads used the "dry-deck" method, meaning no head gaskets were used.