No tach? Tune your exhaust pitch to 166Hz...2500 RPM X4 (V8) exhaust pulses per revolution / 60 seconds....166/sec. Speaking of guitar tuners, an E3 (3rd octave E) is 164Hz..a 3G is 196Hz or 3000 RPM. Hemi air raid sirens use to spin a slotted 'chopper' disk to produce their pitch.
