Mach number a small area around the object's leading edge. (Fig.1b) Fig. 1. "Mach number in transonic airflow around an airfoil; M < 1 (a) and M > 1 (b)." When an aircraft exceeds Mach 1 (i.e. the sound barrier), a large pressure difference is created just in front of the aircraft. This abrupt pressure difference, called a shock wave, spreads backward and outward from the aircraft in a cone shape (a so-called Mach cone). It is this shock wave that causes the sonic boom heard as a fast moving aircraft travels overhead. A person inside the aircraft will not hear this.
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