LSA or Duration to fine tune glasspacks??

318willrun said
when it goes "thip thip thip thip thip", it sounds like a burnt valve 273 2bbl.
when it goes "thap thap thap thap" , it sounds like a 10.1 340 up to snuff.

I have a sound clip of my 360 that may be aligned with the thap thap thap... Will upload it when I get home (I too want know if it sounds right)