So I finally received the adjustable vacuum switch. When the vacuum controlled secondary throttle is activated on the LT5, so is my loud valve. I set it to 12" of vacuum (12 in Hg).
The switch powers a junkyard EGR vacuum solenoid. This couples the vacuum to the muffler valves. It either connects the vacuum to the valve, or vents the vacuum to the atmosphere thru the little foam filter on the 3rd port. It never has a vacuum leak on the source end. Perfect $8 solution (I should have pocketed it but I was feeling honest). The vacuum source is the nearby vacuum ball used for the a/c and air injection diverter valve. The 12v was easy too- I tapped into the under hood lamps which of course aren't even connected anyhow.
This is actually a second MAP sensor just to monitor the secondary throttle system. I 'T'-ed into it. Vacuum here means all 16 runners and injectors are working on the LT5 and it was a simple idea to switch the NPP valve off of this computer controlled load function.
Here it is idling- the loud section of the muffler is blocked off (left pipe). Will try to get a video on Saturday.
