exhaust system idea

[James Weiler]

gang,

I occured to me yesterday to ask a basic question about exhaust systems.
Since it's an advantage to have staged throttle bodies (like in 4 barrel 
carbs) why not do the same for an exhaust?  I imagine such a system could 
have a HUGE pipe between the header and the muffler and then two pipes 
exiting the muffler and going out the back.  However one would have a 
butterfly valve in it and at low RPMs and low engine load it would be 
closed. However at high RPM and/or high load it would open.  This second 
tube could even bypass the muffler to reduce back presure.  OK, what am I 
missing here?  Are the gains too small to be worth it?  This system could 
be quiet most of the time and a screamer when you want/need it to be.

cheers,
james