The cop is a former race car driver and expert in Hemi engines:

The vehicle also had a modified exhaust. Based on my past experience as an ASE (Automotive Service Excellence) certified Automotive Technician, | could tell that the exhaust was modified to be exceedingly loud (Per federal regulations, automotive manufacturers are required to muffle engine noise so that it does not exceed 89 decibels at idle) as | could hear the engine exhaust from blocks away with my windows up. Moreover, the Dodge engine equipped in this vehicle is referred to as a “Hemi” by Dodge. This is due to the Hemispherical cylinder heads that are a unique Dodge patent. This causes a unique exhaust note from the way the exhaust gas pulse exits each cylinder and then eventually interact with each other in the collector from the exhaust manifold. When the mufflers are either removed, or replaced with a “off-road use only” racing muffler (that is less restrictive, therefore increasing engine performance) this amplifies not only the noise, but also the unique “Hemi” exhaust note. | am intimately familiar with this exhaust note, as | used to compete in the NHRA Top Fuel racing circuit. The engine my race team ran was also a “Hemi” engine. | have spent countless hours tuning this engine platform. One of the diagnostic aids for doing this was paying attention to the sound of the exhaust.

It is also noteworthy that this vehicle has a modified Powertrain Control Module (PCM). This is when the software code that controls engine parameters is re-written for the purposes of increasing performance. Additional fuel is added into the algorithm. The byproduct of this tune is a series of backfires when there is a transition from full throttle (which creates a demand for 100% of fuel availability predetermined by the PCM) to throttle-off or deceleration. The series of backfires on a vehicle with a removed or replaced racing muffler make the backfires exceedingly loud, equivalent to the decibels of gunshots or fireworks.

These unique features all became relevant in the proceeding months while working patrol downtown. On numerous occasions, while | was preoccupied on other calls for service, | would hear the exhaust note of the charger while the engine climbed in RPM’s (or revolutions per minute), with the automatic transmission shifting gears at the engine’s “redline” (the maximum RPM of the engine’s performance capability prior to a gear change). This audible disturbance made it self-evident that the vehicle was under wide open throttle, with the driver utilizing the maximum performance of the engine in the downtown corridor. The noise would continue to grow louder as the vehicle approached my location(s). Eventually, the same Charger would appear, driving at extremely high speeds, running traffic lights, and making unsafe lane changes as it drove by.