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The effect of adjusting the kick-off speed to attain a “worst case vehicle configuration” on drive-by noise measurements using test procedure SAE J986OCT88 was investigated. It was determined that similar noise results were obtained for both the “forced worst-case” vehicle and the actual worst-case vehicle. This information is a useful development tool due to the fact that a wide variety of axle ratios, tires, and transmissions are available as options on light duty trucks, making it difficult to determine or obtain the actual worst-case vehicle. Forcing the worst-case configuration allows for the testing of vehicles when the exact worst case vehicle is not available.

The variation in the decoupling effect of exhaust flexible couplings under a vertical preload caused by changes in the direction of the exhaust pipe routing was investigated. Both self-supporting and underbody flexible couplings were tested. The results indicate that, in general, a preload decreases the decoupling efficiency of both types of flexible couplings. In addition, the results indicate that the efficiency of the flexible coupling is effected by the following three conditions: the direction of preload with respect to gravity, the location of the preload relative to the coupling, and the stiffness of the various components of the flexible coupling.