I know many supercars have this kind of setting by having butterfly valves in the exhausts, which open and close the straight portion of the exhausts. those valves are usually vacuum actuated and controlled by the ECU, and can be switched between manually open or automatic depending on the engine load.
I know manual RX8's have this VFAD thing that opens and closes depending on engine load. I just wonder has anyone tried to figure out what kind of condition it opens and closes. this would be a very good way for those who want a quite cruise but loud when accelerating hard.
I've seen some of the aftermarket systems would do the job, but they dont operate with the ECU so you either turn it on or off.
hope what I tried to say makes sense.
http://www.youtube.com/watch?v=AKWysdhEg2w

 

VFAD is vacuum actuated, the specific amount of vacuum needed is probably documented in the service manual or Jon's diy thread on checking VFAD, SSV, etc.

 

^^^ what he said.
Building a vacuum actuated valve is not too hard as it works like a boost controller in the end. The benefits are very little, perhaps sound reduction related only as you said given our intake's complexity and superb functionality

 

VAFD is vacuum actuated, but the signal is from the ECU. I believe it opens at 5,000 RPM.

Or, if you cap off the vacuum, it stays open all the time. Vacuum actually is used to close off the second door.

 

Hell just have have a vaccum switch activate a relay for a MSD RPM switch connected to the cutout.

Then dyno the car with the cutout open and again closed to see where the best time to open it would be an there ya go. It would open only after the specified RPM but only if you were under the proper load.

Pretty sure what I said would work, I'm not an electrnoics scientist but I've done stuff before.

 

yea, that is one way to do it.
I would like the exhaust to open under heavy load above certain rpm to make the "bark" effect.

 

^why reinvent the wheel. The aftermarket active tail silencer do just that with their spring valve.