Mach number which was also unit-first, and may have influenced the use of the term Mach. In the decade preceding faster-than-sound human flight, aeronautical engineers referred to the speed of sound as "Mach's number", never "Mach 1". Mach number is useful because the fluid behaves in a similar manner at a given Mach number, regardless of other variables. As modeled in the International Standard Atmosphere, dry air at mean sea level, standard temperature of , the speed of sound is . The speed of sound is not a constant; in a gas, it increases as the absolute temperature increases, and since atmospheric
Ford Mustang Mach 1 sought to revive the Mach 1 name. While similar to the Bullitt in the use of the Cobra's Brembo front brake rotors, unique Tokico gas shocks and struts, and lower and stiffer springs, the Mach 1 received a huge performance gain over the base GT and even the Bullitt in the form of a unique variant of the DOHC 32-valve 4.6 Liter Modular V8. Commonly known by Mach 1 owners as an "R" code DOHC, (for the unique VIN engine R code) this all-aluminium engine features the same high flow heads as the 2003–2004 SVT Cobra, 2003–2004 Mercury Marauder, 2003–2005