BA onward XR8's had them didn't they?

This was intended that when you step on it it worked like the BBM changed the size of length or cross sectional area of something and supposedly made them sound like and old real v8?

Or so I thought... never really listened to one... The new supercharged 5.0L has the same thing I read somewhere... that flap in the exhaust to change the sound...

Google doesn't seem to find much about it. I've only come accross it mentioned in relation to the FG XR8's, but no specific details or pictures on the system setup.



What I was just thinking is getting a raincap for a truck and putting a spring on it. Basically let the exhaust gases open it up as required, not sure how effective it would be though.