True Dual Exhaust System Strikes Distinctive Note For 2004 Pontiac GTO

DETROIT, MI, June 6, 2003 - A combination of high-technology refinement, global engineering and good old-fashioned ear tuning has ensured the dual exhaust system of the 2004 Pontiac GTO produces a legendary sound in a contemporary car - a rumbling, throaty exhaust note reminiscent of the classic original.

Mechanically, the exhaust system on the GTO consists of two completely independent exhaust paths that run from the manifolds to the outlet pipes, ensuring there is no mixture of exhaust gases. However, creating the necessary "voice" of the vehicle required much more than simple mechanics.

"Anyone who has ever heard a classic GTO knows that distinctive 'sound,'" said Lynn Myers, Pontiac-GMC general manager. "It's very much a part of the character of both the GTO and Pontiac, so we knew we had to recreate that same feeling in the modern version."

The Holden Monaro, on which the new GTO is based, didn't have the "sound" Pontiac needed. "The Monaro is a great performance car, but it's sold as more of a luxury vehicle in Australia so the exhaust note was fairly quiet," said Robert Kraut, GTO marketing director. "From the beginning, everyone knew that the exhaust would have to be 'dialed-up' to give us that special sensory cue that says, 'This is a Pontiac.'"

Throughout the development of the system, exhaust system engineers in opposite hemispheres worked extensively to ensure the new GTO carried all of the audible emotion and virtues associated with its legendary predecessor.

"We had three main priorities for this vehicle right from the outset: power, launch feel, and an exhaust note with lots of character," explained Dave Himmelberg, the GTO program engineering manager. "Our sound objective wasn't about making the exhaust loud. It was about bringing a smile to someone's face as soon as they turned the key."

Early in the vehicle development process, engineers test-drove an original 1964 GTO on loan from the Pontiac historical collection to acquaint themselves with its acoustical traits.

"We wanted to get a real good feel for the sound character of the vehicle," Himmelberg explained, "and that drive provided us with an acoustical baseline from which to start."

"We then listened to the 2002 Corvette, which also has a really good sound with traits we were looking for. With those two baselines, we pretty much had in mind what we wanted to accomplish. Our goal was to come in at a pass-by rate of just under 80 decibels, which is the legal sound limit in some states. But, we knew it couldn't be objectionable. It needed to be a pleasing 80 decibels."

At that point, GM engineers in Australia (where the new GTO is built) and North America worked diligently in a parallel effort to develop an exhaust system that delivered the desired sound and performance characteristics.

"It became a true global effort because the exhaust needed to be developed with parts available in Australia, but acoustically tuned to the spirit of an American classic," Himmelberg said.

Through the efforts of engineers on two continents, a true dual exhaust system was developed and acoustically tuned like a finely crafted woodwind instrument, yet enables the heavy-breathing, low-back pressure needs of the 340-horsepower LS1 V8 powerplant. It consists of:

• Dual catalytic converters, one on each exhaust bank;
  
• Two resonators - acoustical chambers that are tuned to a specific resonant frequency via internally positioned louvers - are positioned between each catalytic converter and the mufflers;
  
• Two mufflers with different internal flow paths (the right muffler flow path is longer than the left). This achieves a harmonic imbalance between the exhaust paths, enabling engineers to essentially mix tonal qualities to achieve desired sounds;
  
• Specifically sized and routed stainless steel pipes to ensure reduced backpressure as well as desired tonal qualities; and,
  
• A single tubular brace that holds the paths together between the converters and resonators to minimize vibration that could adversely affect the tonal qualities of the system.
  
• Using advanced exhaust modeling capabilities, literally dozens of math-based models were analyzed during system development to refine exhaust flow and detail paths in various components for desired tonal qualities.

"We analyzed and re-analyzed sound qualities at every point of the performance curve," Himmelberg said. "We wanted the rumble at start up, more of a throaty roar during acceleration, and it needed to have a pleasing presence at cruise speeds."

However, the true test came down to what the exhaust note sounded like to the human ear, and the emotions it evoked.

"We had about five prototype builds of the system," Himmelberg recalled, "and for each of them, it really boiled down to listening to them on the GTO. We had 14 different scenarios where we'd listen to and analyze the sound - during acceleration, pass-by on streets, pass-by on highways, idle . . . you name it."

"In the end, we knew we had exactly the sound we wanted. It's hard to hear it and not just grin."

General Motors Corp. (NYSE: GM), the world's largest vehicle manufacturer, employs 342,000 people globally in its core automotive business and subsidiaries. Founded in 1908, GM has been the global automotive sales leader since 1931. GM today has manufacturing operations in 32 countries and its vehicles are sold in more than 190 countries. In 2002, GM sold more than 8.6 million cars and trucks, nearly 15 percent of the global vehicle market. GM's global headquarters is at the GM Renaissance Center in Detroit. More information on GM and its products can be found on the company's consumer website at www.gm.com.

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