Slant six Muffler!
To sound good, a slanty's gotta have lots of compression,a stock cam,and a real slow shaking-the-hood idle, like 450; thoop-thoop-thoop-thoop-thoop-thoop........ Problem is, the even firing has no character.It's just thoop-thoop-thoop-thoop-thoop-thoop, all the live-long day. So run dual exhausts;three cylinders down each side, but mix a couple of them up. So you get, on one side;
thoop,-------,-------,thoop-thoop-------; and on the other side,
------,thoop-thoop,--------,-------thoop
Next install two different sounding mufflers.
thoop,--------,--------,thoop-thoop,------- on the one side;and on the other
-------whaapa-whaapa,------,-------whappa
Now you got a rumble.Just don't stand in the middle between the exits, cuz
thoop-whaapa-whaappa-thoop-thoop whaapa-thoop;
will drive you crazy.