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The 2014 Chevrolet Corvette Stingray has an active exhaust system that electronically controls flapper valves to open or close when the driver selects specific driving modes.
By LINDSAY BROOKE

The tones emanating from a car's exhaust pipes - a V8's deep bellow, say, or the piercing wail of a high-revving V12 - have long been inspirations to an enthusiast's ear. What others may deem mere noise can, appropriately tuned, become a symphony of internal combustion.
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With the help of computer modeling and some mechanical gadgetry, automakers are tailoring exhaust notes to more precisely define the character of new models, most vitally in those cars with high-performance credentials. No longer is the goal just to muffle the explosions taking place in the combustion chamber, but to give the engine a voice as readily identified as a Carnegie Hall patron might distinguish a clarinet from an oboe.

"Engines and their exhaust systems are very much like musical instruments in that they have different sound signatures based on the physics of the exhaust gas pulses and how they travel through the pipes," Garry Dunne, director of sound quality engineering at Jaguar Land Rover, said in a telephone interview.

Each "bang" exiting a cylinder and hurtling down the tailpipe includes multiple harmonics, a result of factors including the size and number of engine cylinders and the sequence and timing of their firing. Engineers "tune" the frequencies to create a pleasurable soundtrack - and to meet performance targets and noise regulations - by varying the exhaust pipe diameter and length and installing resonator chambers and mufflers of various shapes and sizes along the route. Materials matter, too: Exhaust manifolds made of thick cast iron attenuate sound differently than those fabricated from thin steel tubing.

Full-time loudness is not the goal. Drivers are more likely to want a hushed growl around town, saving the full-throated roar for the open road.
This duality is how Dr. Dunne describes Jaguar's S versions of the new F-Type sports car, which, along with the Chevrolet Corvette Stingray offer active exhaust systems. In both cars, electronically controlled flapper valves can open or close when the driver selects specific driving modes. Responding to the throttle, the valves operate at very high speed.

"They go from fully open to fully closed in about five milliseconds," said Traci Melville, an acoustics engineer at Tenneco, the supplier company that developed the Corvette's valves. As a concept, active exhaust systems have been entertaining drivers back to the Model T era, when accessory catalogs bulged with ads for "cut out" valves. By the 1990s, with the advent of miniature solenoids, drivers could control the valves in the exhaust system of the Mitsubishi 3000GT.

Since then, automakers have introduced both electronic and pneumatically actuated (Chevrolet Camaro ZL1) valves, while others have opted to pipe real (Cadillac CTS) or electronically reproduced exhaust sound (BMW M5) into the cabin to achieve the same effect.
Creating more sonorous exhaust concerts has become a sophisticated science. It begins with a mathematical model of the engine and its combustion system, said Tim Jackson, Tenneco's executive vice president for technology.

"The model lets us test up to 1,000 variations of an exhaust system right on the computer before we build the first part," he said. "We don't need to start with a real engine. We run the test all night, then the next day we pick up to five systems that look the most promising."
The computer models create audio files, which are played to an automaker's jury through headphones in a dedicated quiet room. The jury chooses the sound packages that most closely match the intended character of the new vehicle.

At Jaguar Land Rover, a team responsible for all new-car performance attributes signs off on the exhaust system acoustics, Dr. Dunne said. He noted additional tricks of the trade that automakers were using to add spice to the tailpipe chorus. On the F-Type S, custom fuel injection and ignition calibration make the exhaust pop and bang like a Tommy gun when the driver lifts off the gas.

"It's the bit that makes the whole driving experience exciting," Dr. Dunne said. "It's a very fine balance in delivering the sound character we want for this car."
 

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I just love to listen to RedHot's symphony is V8 aided by the performance exhaust. They got it purrrrrrrrfect!:cool:
 

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Well ok there you go, you just answered my exhaust question from my other post. See I'm learning already! :)
 

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Love to turn the key or press the button and hear the low grumbling bass tone hit my ear in the quietness of the early morning. Great article...Can really relate!


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Can the performance exhaust be quiet enough? I know that sounds like a stupid question, but my wife's hearing aids amplify sound and she is going to want the car quiet when she is riding with me and wants to talk. I really want the performance exhaust, but I also don't want her saying, "So we are paying $800 a month for a car I can't ride in or enjoy?" With the exhaust in "quiet" mode with the baffles closed, how quiet is it when cruising down the interstate with the performance exhaust vs. the standard exhaust? Does the standard exhaust sound really nice with the baffles wide open? I want it to sound nice (racey/loud) when I'm by myself, but need quiet for her when she is with me.
 

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Can the performance exhaust be quiet enough? I know that sounds like a stupid question, but my wife's hearing aids amplify sound and she is going to want the car quiet when she is riding with me and wants to talk. I really want the performance exhaust, but I also don't want her saying, "So we are paying $800 a month for a car I can't ride in or enjoy?" With the exhaust in "quiet" mode with the baffles closed, how quiet is it when cruising down the interstate with the performance exhaust vs. the standard exhaust? Does the standard exhaust sound really nice with the baffles wide open? I want it to sound nice (racey/loud) when I'm by myself, but need quiet for her when she is with me.
Yes. Even with it set to full open, when you are cruising it is surprisingly quite in the cabin- equivalent to a normal family sedan. It should present no issue.
 

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In my opin, the loudness of this system is overhyped, the only time to me it is LOUD at all is when you start cold in sport or track. And in ANY driving mode, at interstate speed it is sedan quiet in the cabin.
 

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Thanks for the replies gentlemen, that is exactly what I wanted to hear. I can have my performance and she can have the quiet when needed.
 

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I have put flowmasters on my car and it is even quit at 70mph in tour or eco mode!
 
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