What Makes a Car or Truck Sound Raspy

We have all heard it a car or truck rolls by and we want to cover our ears. It sounds like a swarm of angry bees and we all think the same thing…”what an idiot, but what makes the sound like that. No it is not the supercharger that the person says they have added…in fact a super charger unit would probably make the car quieter. The sound is created by adding an exhaust that has not been tuned for the application.

The exhaust is much more than just a pipe that channels the exhaust gases out of the engine bay. It is a specially tuned system that has been meticulously made for that specific car. The resonant sound that comes from a motor during the combustion process creates a pressure wave which can have a positive or negative effect on the engine depending on how the exhaust is shaped.

The headed is the easiest place to see this effect taking place, when the combustion process ends and the air enters the header. At this point the pressure wave is released as well. It will travel down the pipes and bounce off where ever the header turns into one pipe. When this wave moves back towards the engine it can cause unnecessary force on the now exiting gasses which can lower performance. If the header is built specifically to send this wave to impact the outside of the valves just before they open it will have a positive effect on the system. The early impact will create a low pressure area just outside of the valves and the exhaust can leave the engine more freely. Free flowing exhaust means more HP and better gas mileage. Some people believe that removing the header all together will give better performance but in fact the specifically tuned header creates more horse power than an open system.

The rest of the exhaust system is also tuned the same way, it is all about making sure that pressure waves work for the system as opposed to it. If an exhaust system is attached to a car that is not tuned to control this flow the negative pressure waves and lack of sound deadening material causes this sound. Next time you are in traffic and someone is revving their Nissan Sentra with a huge exhaust, just laugh. Not only do they look like a fool but they have also lowered the performance of their car and lost gas mileage to boot. Not to mention that most cars that are being built now are faster than the cars people tend to “modify”. So you can be happy knowing you can smoke them off the line too. In your stock V6 Camry all the while being comfortable and hitting 30 MPG.