[KTL]

Do a search for Jack Olsen. He ended up cutting the collector and shortening up the header itself, as well as changing tail pipe layout. He'd found that resonance was a function of both in his research?

I don't doubt the tail pipe exit style (straight, angled, square, whatever) helping as well. I recall a lot of GM cars back in the 90's had a scalloped end on their tail pipes and it made for a unique (crappy IMO) sound. Also the 4th generation Camaro Z28 that came out in '93 had a strange rectangular tail pipe tip. It also made for a unique thumpy sort of tone.