LSA or Duration to fine tune glasspacks??

What you need is an early opening exhaust valve and a bunch of overlap to mess it all up. How the engine responds to that don't much matter, cuz performance is all about the idle.
But I must say big pipes seem to mellow out the sound of a big cam. I think all that exhaust energy still left by the early opening exhaust tends to arrive at the back bumper with a whole buncha lost energy. And I think those big pipes convert more of that energy to heat. So now you can play with tip shapes to change the sound into something you like.
If you noticed that 4banger example, the tip was rolled over into itself and this makes the worst kindof racket. And the smaller the pipe the worster it is.
But the original 340 type rectangular tips make an interesting burble, even with the stock 268/276/114 cam.I don't personally like it, but many do.
Shot gun tips or boom-tubes, well they are just flat-out nasty megaphones. If they are long enough,straight enough, and just the right diameter,and the engine is making plenty of exhaust energy, they can do tricks. They can make a nice thoop-thoop at idle, that turns into a fairly pleasant sound when cruising, and a raucous roar at WOT.
But my favorite is a 3inch,turn down pipe. This will make a mellow sounding 360, with just barely hinting at the cam. Again, the cruise will be pleasant to all those driving around you, with many people driving in just the right position next to you to enjoy the musical tone coming out of there. But when you stand on it, it will strike pure terror into the heart of your hapless victims. And somewhere between 6000 and 7000 it will shriek like a banshee, and even satan himself will cover his ears and plead for mercy.
Ok so I have run three different cams with three different Dcrs, and all the various differing valve events,thru this same full-length dual 3 inch system with turn-downs. No glasspacs cuz, well, let's not say. But the Dynomaxers on there sounded pretty much the same with all three. I sorta remember the 292/292/108 cam having a bit more rumpidy-rump to it, but honestly, I wasn't paying much attention to the sound back there. Besides idle rpm plays a really big deal on the idle sound.
When I crank back the timing from the drivers seat, so that the rpm gets down to 650 or so then my current 230/237/110 cam starts to reveal itself. Then letting out the clutch, and letting it pull the car outta the parking lot at 550 or so, well then I guess I can hear the thap-thap; but mostly, I'm not paying attention. My mind is already planning my next maximum-impact exit. Just kidding.

So my take on this is; in a streeter with a real street cam,you are gonna have to try waaay too hard to make that thap-thap lol sound. And neither LSA nor duration will play any significant part in the equation.I'm talking street type cams of less than 240* duration. I think the sound is more related to how much exhaust energy reaches the back-bumper,how separated the pulses are,and the idle-speed itself. Of course you have to have headers, to separate the pulses into nice little slugs of energy. And if you pile them all up in a 3-pass muffler and jam them into a 1.875" pipe; well then by the time they get to the back, then it's like a crowd of people trying to exit the stadium through 2 gates; a lot of pushing and shoving, with not much action.And the crowd gets all backed up to homeplate.