Dual Exhaust, Legal or Illegal?

SEMA News—October 2018


By Drew Hardin

Dual Exhaust, Legal or Illegal?


This month’s headline was a cover blurb on the January 1960 issue of Car Craft magazine. Then, as now, performance enthusiasts wanted to keep their cars from running afoul of local law enforcement agencies and their sometimes-vague excessive noise guidelines.

The story’s author, Bob Behme, had “just completed a two-month cross-country survey to find out the facts about mufflers.” The shops and manufacturers he visited, “from Bar Harbor, Maine, to San Diego, California” were “selling a new tone and giving away a new kind of thinking…setting up the nation’s first unified answer to the question, ‘How loud is legal?’”

Today, some states follow a version of SEMA-backed legislation that sets an objective, specific decibel level as the threshold between legal and not. But in most states, noise regulations aren’t as cut and dried. In 1959, when Behme did his tour, he found similar circumstances.

A police officer in Oregon told him, “I rarely stop a car because it’s noisy. If I stop a car for some other traffic violation and the exhaust sounds loud, I throw it in, but it is never the primary reason for a citation.”

A Los Angeles officer took a different approach: “I give a lot of citations for noise. I have no standards except my own ear. Noise bothers me more on some days than on others.”

“So it went across the country,” Behme wrote. “Until muffler manufacturers stepped in, there was no standard for sound. Even today, police are baffled by the interpretation of what a legal exhaust sound really is. This is why muffler manufacturers have begun to police their products. A muffler that is pleasing and legal gives new confidence to both customer and police.”

The 1959 remedy for excessive noise was to “use the longest muffler you can,” muffler engineers told Behme. Such mufflers would provide “a tone loud enough to be exciting, yet low enough to be legal.”

Behme’s six-page story explained how mufflers worked and described muffler types, their construction, the different kinds of packing inside them, how to choose a replacement muffler, and where on the car to position them. That latter topic was illustrated by the ’55 T-Bird in the story’s lead photo, shot at Advanced Muffler Service in Los Angeles. It was “a good example of limited room due to frame members; 24-in. mufflers would be too noisy, consequently illegal. Solution lies in small resonator cans fixed at rear of muffler. Tone remains good, within the law.”

Cutaway photos of mufflers from various companies showed their construction and packing types, whether fiberglass or steel. It’s interesting that most of those mufflers, like those from Fenton and Hollywood Deep-Tone, can now be found only at swap meets or on eBay. Only Porter Mufflers is still a going concern.

“The problem of how loud is loud continues in most states,” Behme wrote. “Since there is no formal manner in which traffic officers can determine legal sound levels [accurate, portable sound-measuring instruments weren’t developed until the ’70s], the decision rests upon the officer’s personal interpretation. This allows for debatable human error.”

Sixty years later, it still does.

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