May 9, 2003

GM develops throaty exhaust note for new Pontiac GTO

Detroit, Michigan – The dual exhaust system of the 2004 Pontiac GTO will have a rumbling, throaty exhaust note reminiscent of the classic original, says the company.

“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.

“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.

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