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 (for use with 4-venturi carbs) versions. The 351C 4V (M code) engine featured 11.0:1 compression and produced at 5400 rpm. This new performance engine incorporated elements learned from the Ford 385 series engine and the Boss 302, particularly the poly-angle combustion chambers with canted valves and the thin-wall casting technology. For 1971, Ford reduced the content of the Mach 1. The standard features of the model were as follows: In 1971, the Mach 1 was available with three 351 Cleveland engines; the H-code 2-V, the M-code 4-V and beginning in May of 1971, the 351CJ (Cobra Jet or GT engine).