Press Releases

New Walker® Exhaust Efficiency Index Allows Comparison of Muffler Performance

November 2, 1999

LAS VEGAS, Nov 2., 1999 - For years the aftermarket exhaust industry has attempted to accurately and simultaneously relate the sound and performance efficiency of exhaust products.

The new Walker® Exhaust Index solves this problem by correlating the interactive between a muffler's sound and its efficiency. The index is a method that numerically quantifies the effectiveness of a muffler based on acoustic levels and backpressure. Using the California Highway Patrol (CHP) Half Meter Static Test maximum sound acceptance level of 95db(A), Walker engineers subtract a chosen application's tested db(A) level and divide this number by the muffler's measured backpressure (in inches of mercury) at an airflow of 200 standard cubic feet per minute. The resulting number is then multiplied by the applicable engine's displacement. This final number is the Walker Exhaust Index and can be used to compare mufflers for the same vehicle application.

The Walker Exhaust Index equation is written as follows:
            ((A-B / C) x D
Where: A= CHP maximum allowed db(A)
      B= Application tested db(A)
      C= Application measured backpressure in inches of mercury
      D= Application engine displacement in liters

As an example, a new Walker® Quite-Flow™ muffler for a Buick Regal with a 3.8L engine produced an index number of 45. Testing of a competitive muffler for the same application results in a Walker Exhaust Index of 13.

"In layman's terms, a high Walker Exhaust Index number indicates a better performing muffler," said Bill Dreyer, chief aftermarket engineer of exhaust systems for Tenneco Automotive. "The difference between the two Walker Exhaust Index numbers indicates that the Quite-Flow muffler is a better performing muffler in terms of combined acoustical performance and exhaust flow efficiency."

Walker engineers also tested mufflers using a modified CHP Half Meter Static Test. This test uses a microphone that is positioned one-half meter from a test vehicle's tailpipe, 18-inches above the ground and at a 45-degree angle. While the CHP conducts its tests with the vehicle's engine at three-quarter rated engine speed. Walker engineers operate the test vehicle engine at a constant 3000 RPM. "We feel this modification to the CHP Static test gives us a more consistent measurement of how a muffler sounds and performs during normal driving conditions," Dreyer said.

All Walker Exhaust Index testing is conducted under strict engineering testing protocol at Walker's Jackson Aftermarket Engineering Facility located in Jackson, Mich.

With worldwide sales of $3 billion, Tenneco Automotive is the leading global manufacturer of ride control and exhaust system components, and operate 70 facilities in 22 countries in North America, Europe, Africa, South America, Australia and the Asia-Pacific region. Its parent company Tenneco (NYSE: TEN) is a global manufacturing company based in Greenwich, Conn. With 1996 revenues of $7 billion.