Point your phone at a car and read RPM off the exhaust note. Record a pass to chart how the power comes on — and scan for the metronomic spark-cut an ignition-cut traction device leaves in the sound.
— rpm
tap Start, then aim the mic at the car
Cyl
Stroke
Octave
÷21××2
Pass
—peak rpm
—seconds
—ramp smoothness
Cut / traction-device scan
amplitude-modulation spectrum · 4–60 Hz · a sharp peak = a periodic cut
—cut cadence
—regularity
—load gate
How to read it. A clean throttle ramp climbs smoothly. The cut scan rectifies the exhaust note into an amplitude envelope and looks for a steady chop in the 4–60 Hz band — the fingerprint of an ignition-cut traction aid trimming power. The load gate only trusts a cut that shows up while RPM is climbing (corner exit), which is where traction control fires; a cut that's there at steady throttle is more likely a misfire or imbalance. EngineScope is an acoustic hint, not proof: it can't tell traction control from an ignition fault (both cut spark), timing-retard systems barely show, and a pack of cars, wind, or PA noise muddies everything. Best as a single-car, close-to-the-fence read. Use it to decide whether to ask your track to tech a car — not to call anyone out yourself. The RPM math assumes one exhaust pulse per cylinder firing; if it reads half or double, nudge the octave.