Harrison Burton looks for progress in second year in Cup
Last week, NASCAR tested the muffler that will be used for Sunday’s Clash at the Coliseum.
“Heresy,” some fans shouted. They argued that it is against the laws of man and nature to throttle racing cars. This noise is an integral part of the fan experience. That you’re not supposed to be able to have conversations during races.
The cars will be very noisy.
The strong is fast
Engines produce energy by burning fuel and air in their cylinders. Each combustion produces high pressure gases which push the piston upwards. The same gases make a loud popping noise as they escape from the cylinder and finally out the exhaust.
At 8,000 rpm, an eight-cylinder engine performs approximately 520 combustions per second. The faster an engine spins, the more combustions per second and the higher the frequency of exhaust noise.
That’s why NASCAR engines sound like grizzlies and F1 engines, which rev at higher speeds, sound more like angry mosquitoes.
Maximum power requires exhausting spent gases from the cylinder as quickly as possible so that the next combustion reaction can begin. And that’s the problem with mufflers, from a racing perspective.
Tram mufflers bounce sound waves from the engine around a metal box. The waves interfere with each other, decreasing the overall volume coming from the exhaust.
Mufflers can also dampen noise by directing the exhaust through a sound deadening material. Borla, the sole supplier of this weekend’s muffler, manufactures commercial racing mufflers that feature a heavy-duty sound deadening material superior to commonly used fiberglass.
Both methods slow the exhaust gases – the first more than the second. The ideal racing muffler decreases sound with minimal reduction in power.
Sound level measurements are in decibels (dB), a unit named after Alexander Graham, not Christopher – and apparently by someone who wasn’t the best spelling.
But decibels don’t tell the whole story. Sound intensity decreases with distance, so you need to specify how far away the sound source was.
The easiest way to explain the decibel scale is to relate it to real-world noises, as I have done below.
Zero dB is the threshold of human hearing. A whisper that you can barely distinguish is around 20 dB. Most everyday noise is between 60 dB and 100 dB, but sometimes louder. Exposure to 130 dB can be painful. A sound of 150 dB can cause permanent hearing damage in a very short time.
Ringing in your ears the day after a rock concert was a high school badge of honor. Older, I wish I had been a little smarter.
Hair cells — not to be confused with ear hair — facilitate hearing. Sound bends these hair-like cells, and the cells convert the sound into electrical signals that the brain interprets. Loud sounds can bend these cells so much that they break.
Unlike animals such as sharks, zebrafish — and even humble chickens — humans cannot grow new hair cells. Once your hearing is damaged, you cannot get it back.
How loud are racing cars?
A noise attenuation study for the proposed Nashville Fairgrounds track measured a single Next Gen car at COTA generating 112 dB in a straight line at 100 feet.
A 2008 study measured the sound level inside a Gen-6 car at an average of 114 dB. The study also compared the sound in the stands, the infield and the stands.
Let’s add these numbers to our graph.
The Next Gen car at 100 feet has about the same volume as a person shouting at maximum volume 1 inch from your ear. The Next Gen car at 100 feet is just a little quieter than sitting inside the Gen-6 car. Bristol reached peak sound levels loud enough to cause permanent hearing damage.
The graph data suggests that the interior of the Next Gen car should be about 10 times louder than the interior of the Gen-6. Some pilots have made new end caps to deal with the extra noise in the cockpit.
Due to the way the sound works, the numbers don’t add up like you’d expect. A Next Gen car may be 112 dB, but two Next Gen cars are more like 115 dB. A full field would only be 5 to 7 dB stronger.
Mufflers won’t choke much
NASCAR expects a 6-10 dB sound reduction with mufflers. A 10dB reduction would make the Next Gen car as loud as the Gen-6 car.
Another way to look at it: good earplugs reduce sound levels by 25 to 30 dB. Wearing earplugs barely allows you to carry on a conversation if you are standing very close to each other and both of you are shouting.
You won’t notice the change in sound inside the track.
You won’t notice a shift this weekend either, despite dropping 30-40 horsepower. The Next Gen car takes about 14 seconds to complete the LA Coliseum quarter-mile track. This means cars won’t go much faster than typical freeway speeds.
If you’re heading to the track this weekend — despite the mufflers — bring earplugs or over-ear headphones. This is especially important for children, as their hearing is more easily damaged.