Quiet mode update! And the cat temp results.
The 392 has sufficient vacuum at the muffler to keep the valves closed even at moderate throttle. The vacuum source is a canister under the hood is equipped with a one way valve, this provides a consistent vacuum to the valves and prevents vacuum drop as the throttle is at a more moderate settings. the performance exhaust control solenoid is under BCM to determine if the muffler valves should be open based on need or throttle demand.
You might think the valves open because the engine looses its ability to have vacuum to keep the valves closed, and this is not the case.
The valves open because the engine needs the extra exhaust flow to provide the extra performance based on the throttle position. This was designed to do exactly that by the engineers with performance in mind. Again all controlled by the computer and the Performance exhaust solenoid.
So, if you need maximum performance you need to stay in the performance mode all the time as the exhaust is at max flow in the performance mode and vacuum is fully removed from the muffler valves when this is selected.
When coming up with this mode wanted to see if the cats would overheat if the valves remained closed all of the time before condoning this mod. Unfortunately it broke and I had to purchase another. I finally was able to measure the difference with a heat gun.With the valve in the close position all the time and after doing some moderate and repeated accelerations the cats would be about 50 degrees hotter then in the stock configuration and just performance mode turned off.
So to summarize, the cats will run a bit hotter with the mod then stock in the quiet mode only because the valves no long respond directly related to throttle settings. So not problems here. The only drawback is a slight loss of performance in the "True Quiet" mode compared to the factory quiet mode.
One final comment, I wanted to find out the wiring on the factory Solenoid valve so I could run the control directly for it perhaps with a relay but have yet to been able to get a good schematic. Once I do I will come up with a circuit to move it from the aux switches and directly to the solenoid. Doing this will provide full automatic operation using the Performance exhaust button.
I have been running my current mod for some time now and I just love the "TRUE" quiet when I want it.
