Why the Manual-Transmission Porsche 911 GT3 Fails California's Noise Test - RoadandTrack.com
Jun 16, 2021 1 min, 40 secs

The California Code of Regulations specifies that highway vehicles must pass a drive-by noise test designed by the Society of Automotive Engineers—specifically, SAE J1470, "Measurement of Noise Emitted by Accelerating Highway Vehicles." This SAE paper goes into extreme detail explaining the design and layout of the ideal testing environment, the proper arrangement of the measuring equipment, the exact condition of the vehicle to be tested, and on and on.

SAE J1470 aims to measure "the highest noise level consistent with urban driving." The exact testing method varies based on vehicle size, power output, peak acceleration rate, and gearing, but generally, it involves a full-throttle run starting at 50 km/h (31 mph) and continuing until the engine reaches its peak-power rpm.

But the Porsche representative did highlight something notable: SAE J1470 is no longer the most up-to-date testing method when it comes to measuring drive-by noise.

The paper reveals itself to be relatively out of date when it comes to automotive drivetrain technology: the standard test procedure assumes that the typical stick-shift vehicle is "equipped with a manually operated gearbox having not more than four forward gear ratios." There are alternative testing parameters for vehicles with highfalutin gearboxes with more than four forward ratios, and SAE has published updated versions of the test method since 1984.

Rather than a full-throttle (or nearly full-throttle) drive-by, J2805 lays out a hugely complex method of calculating the appropriate rate of acceleration for each individual vehicle being tested.

As the very first paragraph of J2805 states, this updated procedure "is based on extensive statistical investigations of vehicle operation in real traffic." J2805 includes techniques appropriate for hybrid vehicles and other advanced drivetrain designs that did not exist when J1470 method was published.

Vehicle noise testing is performed by the California Highway Patrol, as defined by California Code of Regulations Title 13, Section 1046.

So while Porsche assumedly engineered the GT3 to pass the updated J2805 test with both available transmissions, in California, the old method is still the law of the land.

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