(this is a copy of what i've written in other thread)
I have bought both exhausts (for minarelli Hor. LC) and tested with a tuned hebo manston 4 and i can feel the diferences, on all powerband,higher rpm's achieved, yasuni c30 it's a little bit shorter because of the small header, the stinger it's bigger, and if you see the exhausts side by side, you can see the diferences of the cone angles...on my country (portugal), i never seen a dyno for motorcycles, so i can't give you dynographs, but if you search a little on this forum you can find dynograph's like i did, before i buy the c30 i've made a little search to ensure that c30 was better than c21... And it sure is...
http://forum.scooterforum.net/forum/showthread.php?t=98325&page=4&pp=30&highlight=yasuni+c30
click on it to see the graph's
oh, and sorry for my bad english
cheers