This was a two-valve-per-cylinder design, with semi-hemispherical combustion chambers. The latter fact, along with some mechanical bits borrowed from the 5.7-liter Hemi starting in 2008 ...

While the Boss 429 doesn't exactly use Hemi heads, the design is similar enough to earn it the nickname Semi-Hemi. However, Ford took a slightly different path to make the Boss 429 available to ...