[professorman]

Originally Posted by Qmulus

I just wanted to clarify how the PSE is controlled on our 986s. The PSE has two vacuum controlled flaps that are opened by an electrically controlled vacuum solenoid. The solenoid on the 986/996 implementation of the PSE is controlled solely by a relay located in the relay panel. It has no connection to the DME. The only inputs to the PSE control relay are vehicle speed, power, and the dash switch.

The relay defaults to "quiet mode" at startup, and when in "performance sound" mode it also closes the valves between 30 and 45mph. I believe this is to pass some European noise regulations, but you can disable it by disconnecting speed signal or pulling a resistor in the relay. Later Porsche PSE systems were controlled by the DME, but the system on the 986/996 was not.

I bought a late PSE ('03-'04 with bolt-on tip) from a list member and installed the complete system in my car following the factory PSE retrofit installation guide with all the right parts. Other than the valves, the late PSE muffler looks identical to the non-PSE exhaust, with the exception of the Eisenmann (exhaust manufacturer) stamp and part number.

Honestly, the difference between the valves open and valves closed is very subtle. I was expecting more, and have considered modifying my original muffler with a valve system that completely bypasses the muffler rather than just one of the chambers.

California has a very specific noise test which is speed dependent. Porsche makes a lot of decisions to pass this specific test, so it make sense to be speed dependent.

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. Manual-transmission vehicles are tested in either second or third gear;

https://www.roadandtrack.com/news/a36741701/porsche-911-gt3-manual-fails-californias-noise-test/