[rdavis]

Since my car was originally a non NPP car, here's what I did. Put a T in the vacuum line that is routed behind the throttle body. Ran vac line all the way to the trunk . I bought an electric vacuum switch. Ran the line through the switch then split it & connected each to the muffler. Since the mufflers default to the valve open position, when the vac switch is energized it allows engine vac to the mufflers under light load only. Step on it & engine vacuum drops & the valves open. So not a perfect system. With the vacuum switch not energized no vaccum goes to the mufflers so the valves stay in the default open position. Hopes this may give you some ideas. I'm sure there are other ways to do it. Also it is loud on startup for about 2 secs until the engine builds vacuum to close them.