Quick note: this works incredibly well and responds almost instantly in my car because my intake manifold goes from vacuum to boost on throttle since I have a supercharger. It still works on a naturally aspirated car, but with some added delay between full throttle and the valves opening. A much fancier solution is the mild-to-wild NPP actuator sold by forum vendor "Pipedreams"

This will show you how I wired my C6Z06 mufflers to automatically open and close based on throttle input. Here is a video showing them in action:
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The problem: The stock Corvette exhaust is way too quiet, and aftermarket mufflers are too expensive, too heavy, or too loud... Fortunately for us Chevrolet saw it fit to retrofit some of their vehicles with the clever NPP Bi-Modal exhaust that is loud when you want it, but quiet when you don't... For those of us with pre-2008 cars, here is the easiest, quickest, cheapest way to get the NPP action in a car that was not fitted with it in the first place. Why? Because if you leave it open all the time it drones and gets to be very annoying.

First you need NPP mufflers, of course. I bought a pair of C6 Z06 mufflers for about $350 and run them with my Kooks 1 3/4" headers and a 3" catted X-Pipe. Before them I ran GHL exhaust (intolerable drone), then Corsa Sports (raspy, and 22lbs heavier than the GHLs). Before today I was running them open all the time, and the drone was really starting to get to me.

For this, all you need is:

16 feet of 5/32" rubber hose ($15)
2 3/16" vacuum "T"s
1hour or so of your time

First connect the two butterfly actuators via a rubber hose into a 3/16"T". Make sure to loop the hose between the bumper beam an the muffler bracket, so it does not hang down:
http://i529.photobucket.com/albums/dd339/sampowerlabs/npp/DSCF1910.jpg

Use zip ties to make sure that these hoses can not pop off. You will have a vacuum leak if they do:
http://i529.photobucket.com/albums/dd339/sampowerlabs/npp/DSCF1914.jpg

Connect a 15 foot long hose to the T, and loop it through the frame, heading into the rear driver side wheel well:
http://i529.photobucket.com/albums/dd339/sampowerlabs/npp/DSCF1915.jpg

Loop the hose around the fuel tank filler line, then down towards the drivers side door sill. This ensures that the hose stays flush with the wheel well. N/A cars won't have the red Boost-A-Pump there, but fitment is the same:
http://i529.photobucket.com/albums/dd339/sampowerlabs/npp/DSCF1919.jpg

Use a wire, or something similar, to snake the hose on to the front drivers side wheel well, then up along the windshield washer reservoir, and out by the brake booster:
http://i529.photobucket.com/albums/dd339/sampowerlabs/npp/DSCF1917.jpg

"T" into a vacuum line and connect this line into it. Because of my supercharger kit, my brake booster line is "T"ed for the blow off valve and the Kenne Bell Boost a pump pressure sensor; I simply tied it in there.
http://i529.photobucket.com/albums/dd339/sampowerlabs/npp/DSCF1921.jpg

THAT'S IT!!! $25 and about an hour of easy hose routing...
Now, how does it work?
It is very simple: The muffler butterflies are actuated by engine vacuum; when there is vacuum on the intake manifold, they close, quieting the muffler down. When the intake manifold vacuum goes away, they open, making the car loud.
Engine vacuum is proportional to throttle opening; open throttle = no vacuum (or boost in my case), closed throttle = vacuum.

On engine startup, they are open; the engine comes to life with them on loud then they close up and the car quiets down a split second later.
On cruise control, or light cruise, they are closed.
Around 50% throttle they begin to open progressively, and the car becomes louder with increasing throttle application.
Around 75% throttle they go full open an the car is as loud as it is going to be.

Want them open all the time? No problem: just pull the muffler hose off the "T" and cap it off:
http://i529.photobucket.com/albums/dd339/sampowerlabs/npp/DSCF1920.jpg

Or simply crimp the line so the vacuum can't pass through ;)

Now here is what I like and what I dislike about this system:

Dyno testing shows that a supercharged C6 stands to lose as much as 40HP+ with the butterflies closed. Having them all open or all closed is not acceptable because I need them fully open no matter what when I go full throttle, otherwise exhaust backpressure will be excessive.

PROS:
Car starts up with them open, all the time. I wouldn't want it any other way.
Butterflies are always open at high throttle settings, so the mufflers never restrict engine horsepower when I am trying to make power.
Light cruise is now QUIET!!!
No drone!
No need for me to do anything; they open when I want power, they close when I drive mildly.
Simple, light, reliable system.
CHEAP!

CONS:
Deceleration burble is just about gone, since the mufflers are always closed on decel, no matter what.
I have to get out of the car if I want them open all the time.
My car is supercharged, so at WOT, I am actually applying pressure to them.. I believe they will be OK with that, but that remains to be seen.

I ended up going ahead and putting a solenoid in the line so I can switch between full auto and always open. That will be the subject of a future write up...

:thumbsup3: :thumbsup3:

Car sounds great, I like the sound of that blower in the back ground also :woowoo:

Sounds great power labs :thumbsup3:

very interesting, good job!